An54af ci Linear Reguladores

8/12/2019 An54af ci Linear Reguladores

1/44AN54-1

Application Note 54

March 1993

Power Conversion from Milliamps to Amps at Ultra-High

Efficiency (Up to 95%)

and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation.

Burst Mode is a trademark of Linear Technology Corporation.

Dimitry Goder

Randy Flatness

INTRODUCTION

High efficiency is frequently the main goal for powersupplies in portable computers and hand-held equipment.Efficient converters are necessary in these applications to

minimize power drain on the input source (batteries, etc.)and heat buildup in the power components, allowing forsmaller, lighter, and longer-lived systems. Power conver-sion efficiency must be in the 90% range in order to meetthese goals. This application note features power supplycircuits that satisfy these design requirements and attainhigh efficiency over a wide operating range.

The recent development of the LTC1142, LTC1143,LTC1147, LTC1148, and LTC1149 makes ultra-high effi-ciency conversion possible. In addition, the LTC1148,LTC1149, and LTC1142 are synchronous switching regu-

lators, achieving high efficiency conversion at outputcurrents in excess of 10A. These controllers feature a

current mode architecture that has automatic BurstModeTMoperation at low currents. This technology makes90% efficiencies possible at output currents as low as

10mA, maximizing battery life while a product is in sleepor standby mode.

These ultra-high efficiency converters also implementconstant off-time architecture, fully synchronous switch-ing and low dropout regulation. All these features makethis series of converters a really excellent choice for a vastvariety of applications.

Achieving high efficiency is one of the primary goals ofswitching regulator design. Every application circuit shownin this note includes detailed efficiency graphs. Almost all of

the magnetic parts used in the circuits are standard prod-ucts, available off-the-shelf from various manufacturers.


2/44

Application Note 54

AN54-2

TABLE OF CONTENTS

Buck

LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology ................................................................Figure 1 AN54-3LTC1148: (5V-14V to 5V/2A) Buck Converter .................................................................................................................. Figure 2 AN54-4LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology...................................... Figure 3 AN54-5LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology............................................................. Figure 4 AN54-6LTC1148: (4V-14V to 3.3V/2A) Buck Converter with Surface Mount Technology............................................................. Figure 5 AN54-7LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter ..................................................................................... Figure 6 AN54-8LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter .................................................................................... Figure 7 AN54-9LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter........................................................................................... Figure 8 AN54-10LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs ................ Figure 9 AN54-11LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter....................................................................................... Figure 10 AN54-12LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter........................................................................................ Figure 11 AN54-13LTC1149: (16VRMSto 13.8/10A) Buck Converter ........................................................................................................... Figure 12 AN54-14LTC1149: (32VRMSto 27.6V/5A) Buck Converter ........................................................................................................... Figure 13 AN54-15LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology .............................................................. Figure 14 AN54-16LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ...........................................................Figure 15 AN54-17

LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology .......................................................... Figure 16 AN54-18LTC1148: (10V-14V to 5V/10A) High Current Buck Convert .......................................................................................... Figure 17 AN54-19LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter................................................................... Figure 18 AN54-20LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter................................................................. Figure 19 AN54-21LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter ............................................................... Figure 20 AN54-22LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter ................................................................................ Figure 26 AN54-28LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter ................................................................................ Figure 27 AN54-29LTC1148HV-3.3 (4V-18V to 3.3V/1A) High Voltage Buck Converter .............................................................................. Figure 28 AN54-30LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter ............................................................................... Figure 29 AN54-31LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter ...................................................... Figure 30 AN54-32LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter ............................ Figure 31 AN54-34Single LTC1149: Dual Output Buck Converter ............................................................................................................... Figure 35 AN54-38LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter ................................................................................ Figure 36 AN54-39

LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter......................................................................... Figure 37 AN54-40Buck-Boost and Inverting Topologies

LTC1148: (4V-14V to 5V/1A) SEPIC Converter .............................................................................................................. Figure 21 AN54-23LTC1148: (4V-14V to 5V/0.5A, 5V/0.5A) Split Supply Converter ................................................................................. Figure 22 AN54-24LTC1148: (4V-10V to 5V/1A) Positive-to-Negative Converter ...................................................................................... Figure 23 AN54-25LTC1148: (5V-12V to 15V/0.5A) Buck-Boost Converter .............................................................................................. Figure 24 AN54-26

Boost

LTC1148: (2V-5V to 5V/1A) Boost Converter ................................................................................................................. Figure 25 AN54-27

Battery Charging Circuits

LTC1148: High Efficiency Charger Circuit ...................................................................................................................... Figure 32 AN54-35LTC1148: High Voltage Charger Circuit ......................................................................................................................... Figure 33 AN54-36

LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger ......................................... Figure 34 AN54-37Appendix A

Topics of Common Interest ........................................................................................................................................................... AN54-40

Appendix B

Suggested Manufacturers ............................................................................................................................................................. AN54-42


3/44AN54-3

Application Note 54

LTC1148: (5V-14V to 5V/1A) Buck Converter withSurface Mount Technology

A basic LTC1148 application is shown in Figure 1A. This isa conventional step-down converter that provides 5V out-

put at 1A maximum output current. All the componentsused are surface mounted and no heat sink is required.During Q1 on-time, inductor L1's current is sensed by R2and monitored by an internal current sensing comparator.To filter out noise from the current sense waveform, C6 isadded to the circuit. When the current ramp reaches apreset value, Q1 is turned off, and a clamp diode D1 startsconducting for a short period of time, until the internalcontrol logic senses that Q1 is completely off. ThenNDRIVEoutput goes high turning Q2 on, which shorts outD1. This provides synchronous rectification and signifi-cantly reduces conduction losses during Q1s off-time.

This regulator has a constant off-time defined by the timingcapacitor C5. To control the output, on-time is varied,

changing the operating frequency and therefore, the dutycycle. If the input voltage is reduced, frequency decreaseskeeping output voltage at the same level. Q1s on-timestretches to infinity with low input voltage, providing 100%

duty cycle and very low dropout. Under dropout condi-tions, the output voltage follows the input, less any resis-tive losses in Q1, L1 and R2.

Under conditions of light output currents, the regulatorenters Burst Mode operation to ensure high efficiency.Continuous operation is interrupted by an internal voltagesensing comparator with built-in hysteresis. in this modeboth Q1 and Q2 are turned off and the comparator monitorsdecreasing output voltage. When the output capacitordischarges below a fixed threshold, operation resumes fora short period of time bringing the output voltage back to

normal. Then the regulator shuts down again conservingquiescent current. Under Burst Mode operation the outputripple is typically 50mV as set by the hysteresis in thecomparator.

Kool Mis a registered trademark of Magnetics, Inc.

Figure 1A. LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology

AN54 F01AC1 (Ta)

C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200 IRMS= 0.775AC7 AVX (Ta) TPSE227K010R0080 ESR = 0.080 IRMS= 1.285AQ1 SILICONIX PMOS BVDSS= 20V RDSON= 0.100 CRSS = 400pF Qg= 50nCQ2 SILICONIX NMOS BVDSS= 30V RDSON= 0.050 CRSS = 160pF Qg= 30nCD1 MOTOROLA SCHOTTKY VBR = 40V

ITH

CT

SGND PGND

LTC1148-5

VINPDRIVE

SENSE +

SENSE

NDRIVE

+

C60.01F

+

VIN5V TO 14V

C11F

R11k

C43300pFX7R

C5390pFNPO

10

4

1

8

7

14

Q1Si9430DY

Q2Si9410DY

D1MBRS140T3

C322F 225V

100H

R20.1

5V1A

C7220F 10V

3

11

12

SHUTDOWN

6

C20.1F

+

L1

1

2

4

3

R2 KRL SP-1/2-A1-0R100J Pd = 0.75W

L1 COILTRONICS CTX100-4 DCR = 0.175Kool MCORE

ALL OTHER CAPACITORS ARE CERAMIC

QUIESCENT CURRENT = 180ATRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 200mA


4/44

Application Note 54

AN54-4

Figure 1B shows efficiency versus output current for threedifferent input voltages. Generally speaking, efficiencydrops as a function of input voltage due to gate chargelosses and LTC1148 DC bias current. The curves converge

at maximum output current as these losses become lesssignificant.

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 1

AN54 F01B

60

VIN= 6V

VIN= 10V

VIN= 14V

Figure 1B. LTC1148: (5V-14V to 5V/1A) Buck ConverterMeasured Efficiency

Figure 2A. LTC1148: (5V-14V to 5V/2A) Buck Converter

AN54 F02A

C1 (Ta)

C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200 IRMS= 0.775A

C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080 IRMS= 1.285A

Q1 SILICONIX PMOS BVDSS= 20V RDSON= 0.100 CRSS = 400pF Qg= 50nC

Q2 SILICONIX NMOS BVDSS= 30V RDSON= 0.050 CRSS = 160pF Qg= 30nC

D1 MOTOROLA SCHOTTKY VBR = 40V

R2 KRL SL- 1-C1-0R050J Pd = 1W

L1 COILTRONICS CTX62-2-MP DCR = 0.040 MPP CORE (THROUGH HOLE)


ITH

CT

LTC1148-5

VIN

SENSE +

SENSE

+

C60.01F

+

VIN5V TO 14V C1

1F

R11k

C43300pFX7R

C5470pFNPO

10

4

1

8

7

14

Q1Si9430DY

Q2Si9410DY

D1MBRS140T3

C322F 325V

L162H

R20.05

5V2A

C7220F 2 10V

QUIESCENT CURRENT = 180A

TRANSITION CURRENT (Burst ModeOPERATION/CONTINUOUS OPERATION) = 400mA

3

11

12

SHUTDOWN

6

C20.1F

+

SGND PGND

PDRIVE

NDRIVE

LTC1148: (5V-14V to 5V/2A) Buck Converter

A step-down regulator with 2A output current capability isshown in Figure 2A. To provide higher output power levelsthe sense resistor value is decreased, thus increasing thecurrent limit. This also increases maximum allowableripple current in the inductor, so its value can be reduced.Note that timing capacitor C5 is changed to optimizeperformance for a standard inductor value. In this FigureC7 consists of two parallel capacitors ensuring minimumcapacitance requirement for all conditions. A circuit boardhas been laid out for this circuit and has subsequentlybeen thoroughly tested under full operating conditionsand optimized for mass production requirements. A Ger-ber file for the board is available upon request.


5/44AN54-5

Application Note 54

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 2

AN54 F02B

60

VIN= 6V

VIN= 10V

VIN= 14V

1

Figure 2B. LTC1148: (5V-14V to 5V/2A) Buck ConverterMeasured Efficiency

LTC1148: (5V-14V to 5V/2A) High Frequency BuckConverter with Surface Mount Technology

Figure 3A presents essentially the same circuit as Figure2A, but implementing changes to operate at a higher

frequency. Timing capacitor C5 is reduced to achievehigher switching rate. This approach allows the use of asmaller value inductor with surface mount technology,resulting in a more compact design.

C1 (Ta)


R2 KRL SL-1-C1-0R050J Pd = 1W



ITH

CT

LTC1148-5

VIN

SENSE +

SENSE

+

C60.01F

+

VIN5V TO14V

C11F

R11k

C43300pFX7R

C5220pFNPO

10

4

1

8

7

14

Q1Si9430DY

Q2Si9410DY

D1MBRS140T3

C322F 325V

33H

R20.05

5V2A

C7220F 2 10V

QUIESCENT CURRENT = 180ATRANSITION CURRENT (Burst ModeOPERATION/CONTINUOUS OPERATION) = 400mA

3

11

12

SHUTDOWN

6

C20.1F

+

L1

1

2

4

3

AN54 F03A

SGND PGND

PDRIVE

NDRIVE

Figure 3A. LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology


6/44

Application Note 54

AN54-6

Figure 4A. LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology

Let us compare efficiency graphs in Figures 2B and 3B.Gate charge losses are directly proportional to operatingfrequency, and as a result the efficiency of Figure 3A is

decreased. However, the effect is most noticeable at highinput voltages and low currents. At maximum load I2Rlosses dominate so that the regulator performance variesonly slightly. These two circuits illustrate the fact that best

overall efficiency is reached at moderate frequencies. Theyrepresent a nice example of compromising between regu-lator compactness and efficiency.

AN54 F04A

C1 (Ta)


R2 KRL SP-1/2-A1-0R100J Pd = 0.75W



ITH

CT

LTC1148-3.3

VIN

SENSE +

SENSE

+

C60.01F

+

VIN4V TO 14V C1

1F

R11k

C43300pFX7R

C5560pFNPO

10

4

1

8

7

14

Q1

Si9430DY

Q2Si9410DY

D1MBRS140T3

C322F 225V

100H

R20.1

3.3V1A

C7220F 10V

QUIESCENT CURRENT = 180ATRANSITION CURRENT (Burst ModeOPERATION/CONTINUOUS OPERATION) = 250mA

3

11

12

SHUTDOWN

6

C20.1F

+

L1

1

2

4

3

SGND PGND

PDRIVE

NDRIVE

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 1

AN54 F03B

60

VIN= 6V

VIN= 10V

VIN= 14V

2

Figure 3B. LTC1148: (5V-14V to 5V/2A) High FrequencyBuck Converter Measured Efficiency

LTC1148: (4V-14V to 3.3V) Buck Converters withSurface Mount Technology

Figures 4A and 5A show application circuits for theLTC1148-3.3 which provides a fixed 3.3V output. Thecircuits deliver 1A and 2A output currents, and use exactlythe same circuit configuration and component values asFigures 1A and 2A. Even though the LTC1148 can achievelow dropout, the minimum input voltage is limited to 4V tomeet requirements for power MOSFET gate drive, and toensure proper operation of the LTC1148 internal circuitry.


7/44AN54-7

Application Note 54

Low output voltage causes efficiency degradation at lightloads when the chips DC supply current and gate chargecurrent play major parts in total losses. Figures 4B and


5B illustrate this point as the efficiency falls off below10mA output current. High input voltage compounds theproblem.

Figure 4B. LTC1148: (4V-14V to 3.3V/1A) Buck ConverterMeasured Efficiency

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 1

AN54 F04B

60

VIN= 5V

VIN= 10V

VIN= 14V

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 2

AN54 F05B

60

1

VIN= 5V

VIN= 10V

VIN= 14V

Figure 5B. LTC1148: (4V-14V to 3.3V/2A) Buck ConverterMeasured Efficiency

AN54 F05A

C1 (Ta)C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200 IRMS= 0.775A






L1 COILTRONICS CTX50-2-MP DCR = 0.032MPP CORE (THROUGH HOLE)


ITH

CT

LTC1148-3.3

VIN

SENSE +

SENSE

+

C60.01F

+

VIN4V TO 14V C1

1F

R11k

C43300pFX7R

C5470pFNPO

10

4

1

8

7

14

Q1Si9430DY

Q2Si9410DY

D1MBRS140T3

C322F 325V

L1

50H

R2

0.05

3.3V2A

C7220F 210V


TRANSITION CURRENT (Burst ModeOPERATION/CONTINUOUS OPERATION) = 450mA

3

11

12

SHUTDOWN

6

C20.1F

+

SGND PGND

PDRIVE

NDRIVE


8/44

Application Note 54

AN54-8

LTC1148: (5V to 3.3V/5A) High EfficiencyStep-Down Converter

Many new microprocessor designs require 3.3V, yet theyare used in systems where 5V is the primary source of

power. A high efficiency 5V to 3.3V converter is drawn inFigure 6A. It supplies up to 5A load using only surfacemount components. Two P-channel MOSFETs are con-nected in parallel to decrease their conduction losses.Efficiency at 5V input is 90%; this means only 1.6W is lost.The lost power is distributed between RSENSE, L1 and thepower MOSFETs, thus no heat sinking is required. OUTPUT CURRENT (A)

EFFICIENCY(%)

100

90

80

700.001 0.1 1 10

AN54 F06B

0.01

Figure 6B. LTC1148: (5V to 3.3V/5A)Buck Converter Measured Efficiency

Figure 6A. LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter

0V = NORMAL>2V = SHUTDOWN

Q1Si9433DY

Q2Si9433DY

+C11F

C20.1F

C70.01F

L15H

R20.02

VOUT3.3V5A

+

VIN5V

C5150pFNPO

C43300pF

R1470 + C6

220F10V3

C333F6.3V2

D1MBRS140T3

AN54 F06A

Q3Si9410DY

ITH

CT

SGND PGND

LTC1148-3.3

VINPDRIVE

SENSE +

SENSE

NDRIVE

SHUTDOWN10

4

1

8

7

14

3

11

12

6

C1 TANTALUM

C3 PANASONIC ECG-COJB330


Q1, Q2 SILICONIX PMOS BVDSS= 12V DCRON= 0.075 Qg= 60nC

Q3 SILICONIX NMOS BVDSS= 30V DCRON= 0.050 Qg= 30nC


R2 KRL MP-2A-C1-0R020J Pd = 3W

L1 COILTRONICS CTX02-12483-1


9/44AN54-9

Application Note 54

LTC1148: (5V to 3.5V/3A) High EfficiencyStep-Down Converter

Some processors require 3.5V or other intermediate volt-age derived from a 5V supply. A good solution for them is

the circuit in Figure 7A. An adjustable version of theLTC1148 allows precise output voltage adjustment, whilepreserving efficiencies of 95%. The output voltage is setby resistors R3 and R4.

OUTPUT CURRENT (A)

0.001

EFFICIENCY(%)

100

95

90

85

80

75

70

65

600.01 0.1

AN54 F07B

1 4

Figure 7B. LTC1148: (5V to 3.5V/3A)Measured Efficiency

Q1Si9433DY

AN54 F07A

C6, 0.01F

C20.1F

VOUT3.5V3A

SHUTDOWN100pF

C6100F 10V3

C322F 25V2

R410k1%

L1

10H

LTC1148

+

C43300pF

X7R

1

2

3

4

5

6

7

14

13

12

11

10

9

8

PDRIVE

NC

VIN

CT

INT VCC

ITH

SENSE

NDRIVE

NC

PGND

SGND

SHUTDOWN

ADJ

SENSE+

C3 AVX (Ta) TPSD226M025R0200 ESR = 0.20 IRMS= 0.866A

C6 AVX (Ta) TPSD107M01R0100 ESR = 0.10 IRMS

= 1.225A

Q1 SILICONIX PMOS BVDSS= 12V DCRON= 0.110 Qg = 20nC

Q2 SILICONIX NMOS BVDSS= 30V DCRON= 0.05 Qg = 30nC


R2 KRL SL-C1-1/2-0R033J Pd = 1/2W

L1 COILTRONICS CTX10-4 DCR = 0.038 Kool MCORE

+

R318.2k1%

R20.033

D1MBRS130T3

R1510

Q2Si9410DY

VOUT= 1.25V (1 + R3/R4)

+

VIN5V+

C5180pF

NPO

Figure 7A. LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter


10/44

Application Note 54

AN54-10

LTC1149: (10V-48V to 5V/2A) High VoltageBuck Converter

Previous circuits can accept inputs up to 14V. If higherinput voltage is required the LTC1149 can be used. This IC

is designed for inputs of up to 48V. A basic step-downapplication circuit is shown in Figure 8A. It operates in thesame fashion as the circuit in Figure 1A and provides5V/2A output. However, different MOSFETs are used sincethey must withstand 48V between source and drain. Highcurrent efficiency exceeds 92% over wide range of inputvoltages. Since the control and drive circuitry are powereddirectly from the input line, DC bias current and gatecharge current result in slightly lower efficiency at lightand moderate loads due to high input voltage (relative toLTC1148). This characteristic is eliminated in the circuit ofFigure 11A. A circuit board has been laid out for this circuitand has subsequently been thoroughly tested under full

operating conditions and optimized for mass productionrequirements. A Gerber file for the board is available uponrequest.

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 2

AN54 F08B

60

1

VIN= 12V

VIN= 48V

VIN= 36V

VIN= 24V

Figure 8B. LTC1149: (10V-48V to 5V/2A) High VoltageBuck Converter Measured Efficiency

AN54 F08A

C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170IRMS= 1.280A

C4 (Ta)C10 SANYO (OS-CON) 10SA22OM ESR = 0.035 IRMS= 2.360A

Q1 IR PMOS BVDSS= 60V RDSON= 0.280 CRSS = 65pF Qg= 19nC

Q2 IR NMOS BVDSS= 60V RDSON= 0.100 CRSS = 79pF Qg= 28nC

D1 SILICON VBR = 75V


R2 KRL NP-1A-C1-0R050J Pd = 1W

L1 COILTRONICS CTX62-2-MP DCR = 0.040MPP CORE


VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-5

PGATE

VIN

SENSE +

SENSE

NGATE

D11N4148

+

C90.01F

+

VIN10V TO 48V C1

0.1F

+C41F

C50.1F

C6

0.068FZ5U

R11k

C73300pFX7R

C8680pFNPO

3

5

16

10

15

7

6

1

4

9

8

13

C30.047F

Z5U

Q1IRFU9024

Q2IRFU024

D2MBR160

C2330F63V

L162H

R20.05

5V

2A

C10220F 210V

QUIESCENT CURRENT = 1.5mA

TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA

2

11

12

14

SGND PGND

PDRIVE

RGND

Figure 8A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter


11/44AN54-11

Application Note 54

LTC1149: (10V-48V to 5V/2A) High Voltage BuckConverter with Large P-Channel and N-ChannelMOSFETs

Figure 9A is similar to Figure 8A with much larger MOSFETs

(TO220 package). These transistors have lower RDS(ON)which reduces their I2R losses by roughly a factor of 2.However, the efficiency improves (compared to Figure8B) only at 2A output current with minimum input voltage.Under other conditions higher gate capacitance causesincreased gate charge current leading to higher driverloss. Also for high input voltages (roughly greater than24V), transition losses play a significant part. These lossesare proportional to the reverse transfer capacitance CRSS,maximum output current, and the square of input voltage.Larger CRSSfor the oversized P-channel MOSFET causesan efficiency drop (especially for higher input voltages).

Remember, the best MOSFET selection depends on theparticular application.

Figure 9B. LTC1149: (10V-48V to 5V/2A) Measured Efficiencywith Large P-Channel and N-Channel MOSFETs

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 2

AN54 F09B

60

1

VIN= 12V

VIN= 48V

VIN= 24V

VIN= 36V

AN54 F09A

C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170IRMS= 1.280A

C4 (Ta)

C10 SANYO (OS-CON) 10SA220M ESR = 0.035 IRMS= 2.360A








VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-5

VIN

SENSE +

SENSE

D11N4148

+

C90.01F

+

VIN10V TO 48V

C10.1F

+C41F

R11k

C73300pFX7R

C8680pFNPO

3

5

1610

15

7

6

1

4

9

8

13

C30.047FZ5U

Q1IRF9Z34

Q2IRFZ34

D2MBR160

C2330F63V

L162H

R20.05

5V

2A

C10220F 210V



2

11

12

14

PGATE

NGATESGND PGND

PDRIVE

RGND

C50.1F

C6

0.068FZ5U

Figure 9A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs


12/44

Application Note 54

AN54-12

LTC1149: (10V-48V to 3.3V/2A) High VoltageBuck Converter

If 3.3V has to be generated efficiently from a high voltageinput, use the circuit of Figure 10A. It copies the configu-ration presented in Figure 8A but uses the LTC1149-3.3regulator to provide a precise 3.3V output. In spite ofthe high input and low output voltages, efficiency stillreaches 92%.

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 2

AN54 F10B

60

1

VIN= 48V

VIN= 12V

VIN= 36V

VIN= 24V

Figure 10B. LTC1149: (10V-48V to 3.3V/2A) High VoltageBuck Converter Measured Efficiency

Figure 10A. LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter

AN54 F10A

C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 30 ESR = 0.170IRMS= 1.280A

C4 (Ta)






R2 KRL NP-1A-C1-0R050J Pd = 1WL1 COILTRONICS CTX50-2-MP DCR = 0.032MPP CORE


VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-3.3

VIN

SENSE +

SENSE

D11N4148

+

C90.01F

+

VIN10V TO 48V

C10.1F

+C41F

C50.1F

C60.068F

Z5U

R11k

C73300pFX7R

C8470pFNPO

3

5

16

10

15

7

6

1

4

9

8

13

C30.047FZ5U

Q1IRFU9024

Q2IRFU024

D2MBR160

C2330F63V

L150H

R20.05

3.3V2A

C10220F 10V

QUIESCENT CURRENT = 1.5mATRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA

2

11

12

14

PGATE

NGATE

SGND PGND

PDRIVE

RGND


13/44AN54-13

Application Note 54

AN54 F11A

C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 30 ESR = 0.170IRMS= 1.280A

C4 (Ta)









VCC

VCC

CAP

SD2

ITH

CT

LTC1149

VIN

SENSE+VFB

SENSE

D11N4148

+

C90.01F

D41N4148

+

VIN10V TO 48V C1

0.1F

+ C41F

R11k

Q32N3904

Q42N3906

33k

10k 33k

D35.1V

432k1%

49.9k1%C7

3300pFX7R

C8200pFNPO

3

5

16

15

7

6

1

4

9

10

8

13

C30.047FZ5U

Q1

IRF9Z34

Q2IRFZ34

D2MBR160

C2330F63V

L162H

R20.05

VOUT12V2A

C10220F 210V



2

11

12

14

PGATE

NGATESGND PGND

PDRIVE

RGND

C50.1F

C60.068F

Z5U

10k

Figure 11A. LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter

LTC1149: (10V-48V to 12V/2A) High VoltageBuck Converter

The LTC1149 contains an internal 10V low dropout linearregulator to provide power to the control circuitry. It

actually means that the DC bias current as well as the gatecharge current come directly from the input line, causingslight efficiency degradation, especially for high inputvoltages (additional power is dissipated by the internalregulator). A solution for this problem is presented inFigure 11A. When the output level reaches about 5V, ZenerD3 starts conducting and saturates Q3, which in turnswitches Q4 on. Now VCCpins 3 and 5 are powered directlyfrom the output. Losses caused by DC current and gatecharge current are significantly reduced allowing im-proved efficiency at high input voltage.

The regulator output must be set up for an output voltageless than 14.5V to provide a margin for the LTC1149 pin5 absolute maximum rating of 16V. It should also be

observed that Q4 turns on when the output is less than 10V(the internal regulator output) and stays on or off under allconditions.

Figure 11B. LTC1149: (10V-48V to 5V/2A) MeasuredEfficiency with Large P-Channel and N-ChannelMOSFETs

OUTPUT CURRENT (A)

0.001

EFFICIENCY(%)

100

95

90

85

80

75

70

65

600.01 0.1

AN54 F11B

1 10

VIN= 15V

VIN= 48V

VIN= 36V


14/44

Application Note 54

AN54-14

LTC1149: High Power Buck Converters

Figures 12A and 13A are examples of high power (morethan 100W) converters that use the LT1149. The regula-tors are powered from the full wave rectified output of a16VRMSto 32VRMStransformer. Input capacitance is verybulky, but it has to ensure that ripple valleys do not dipbelow the minimum regulator input requirement. Thecircuit in Figure 13A has additional gate driver circuitswhich are required to improve MOSFET switching times.Overall efficiency goes as high as 98%! Remember, atthese output current levels layout becomes extremelyimportant, and all the recommendations from the LTC1149data sheet must be closely followed.

COUT, 1500F25V, 2

PGATE

VIN

VCC

PDRIVE

VCC

CT

ITH

SENSE

CAP

SD2

RGND

NGATE

PGND

SGND

VFB

SENSE+

SHUTDOWN(NORMALLY GND)

100pF

VIN16VRMS

RECTIFIED

+

+

10F

0.33F

0.33F

R2205k

100

LTC1149

100

3300pFCT

270pF

470

RS0.0082

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

Q1RFG60P06E

Q2IRFZ44

D2MBR380

D11N4148

AN54 F12A

OUTPUTGROUNDCONNECTION

L33H

1.5F63VWIMA

1FWIMA

33k

VOUT13.8V10A

1000pF

COUTPANASONIC HFQ SERIESD2 MOTOROLA SCHOTTKYQ1 HARRIS PMOS BV DSS= 60V RDSON= 0.03

0.22F CIN

20000F35V

+

R120.5k1%

Figure 12A. LTC1149: (16VRMSto 13.8V/10A) Buck Converter

OUTPUT CURRENT (A)

0.01

EFFICIENC

Y(%)

100

95

90

85

80

75

70

650.1 1 10

AN54 F12B

Figure 12B. LTC1149: (16VRMSto 13.8V/10A)Buck Converter Measured Efficiency


15/44AN54-15

Application Note 54

COUT, 1000F35V

PGATE

VIN

VCC

PDRIVE

VCC

CT

ITH

SENSE

CAP

SD2

RGND

NGATE

PGND

SGND

VFB

SENSE+

SHUTDOWN(NORMALLY GND)

100pF

VIN32VRMS

RECTIFIED

+

+

10F

0.33F

MPSW06

MPSA56

PDRIVE

BUFFER

NDRIVE

BUFFER

0.33F

R2432k

100

LTC1149

100

3300pFCT

150pF

470

RS0.016

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

Q1SMP40P06

Q2IRFZ34

D2MBR380

AN54 F13A

OUTPUTGROUNDCONNECTION

L62H

1N4148

D11N4148

1.5F63VWIMA

1FWIMA

33k

VOUT27.6V5A

1000pF

0.22F

CIN

5000F75V

+

R120.5k1%

MPSA56

COUTPANASONIC HFQ SERIESD2 MOTOROLA SCHOTTKYQ1 SILICONIX PMOS BV DSS= 60V RDSON= 0.045

Figure 13A. LTC1149: (32VRMSto 27.6V/5A) Buck Converter

OUTPUT CURRENT (A)

0.01

EFFICIENCY(%)

100

95

90

85

80

75

70

650.1 1 10

AN54 F13B

Figure 13B. LTC1149: (32VRMSto 27.6V/5A) Buck Converter Measured Efficiency


16/44

Application Note 54

AN54-16

LTC1147: (5V-14V to 5V/1A) Buck Converter withSurface Mount Technology

The LTC1147 (Figure 14A) is a great way to implement ahigh efficiency regulator using a minimum number ofexternal components and occupying the least board space.This regulator provides many advantages of the LTC1148including constant off-time configuration, low dropoutregulation and Bust Mode operation, comes in a smallerpackage and does not require the N-channel MOSFET. Theonly sacrifice made is synchronous rectification whichdegrades the efficiency of this circuit up to three percent-age points. Compare efficiency graphs in Figures 1B and14B! Since the clamp diode D1 conducts all the timeduring the off-time, a larger diode (MBRD330) is used forthis circuit. The LTC1147 is an excellent choice where theoutput current is less than 1A, and where the input voltageis less than twice the output voltage.

Figure 14B. LTC1147: (5V-14V to 5V/1A)Buck Converter Measured Efficiency

OUTPUT CURRENT (A)

0.00150

EFFICIENC

Y(%)

70

80

90

100

0.01 0.1 1

AN54 F14B

60

VIN= 6V

VIN= 10V

VIN= 14V

AN54 F14A

C2 AVX (Ta) TPSD226K025R0200 ESR = 0.200 IRMS= 0.775AC5 AVX (Ta) TPSE227K010R0080 ESR = 0.080 IRMS= 1.285AQ1 SILICONIX PMOS BVDSS= 20V RDSON= 0.100 CRSS = 400pF Qg= 50nCD1 MOTOROLA SCHOTTKY VBR = 30V

R2 KRL SP-1/2-A1-0R100J Pd = 0.75W



ITH

CT

GND

LTC1147-5

VIN

SENSE +

SENSE

+

C50.001F

+

VIN5V TO 14V

R11k

C33300pFX7R

C4390pFNPO

2

8

5

4

Q1Si9430DY

D1MBRD330

C222F x 225V

100H

R20.1

5V

1A

C6220F 10V

QUIESCENT CURRENT = 190ATRANSITION CURRENT (Burst ModeOPERATION/

CONTINUOUS OPERATION) = 170mA

1

7

SHUTDOWN6

+

L1

1

2

4

3

C10.1F

3

PDRIVE

Figure 14A. LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology


17/44AN54-17

Application Note 54

OUTPUT CURRENT (A)

0.00150

EFFICIENCY(%)

70

80

90

100

0.01 0.1 1

AN54 F15B

60

VIN= 5V

VIN= 10V

VIN= 14V

Figure 15B. LTC1147: (4V-14V to 3.3V/1A)Buck Converter Measured Efficiency

LTC1147: (4V-14V to 3.3V/1A) Buck Converter withSurface Mount Technology

Figure 15A shows another compact circuit with theLTC1147 series. It generates 3.3V/1A output using thesame configuration as in the previous example. Despitethe lack of synchronous rectification, efficiency approaches95% with 5V input.

AN54 F15A

C2 AVX (Ta) TPSD226K025R0200 ESR = 0.200 IRMS= 0.775AC6 AVX (Ta) TPSE227K010R0080 ESR = 0.080 IRMS= 1.285AQ1 SILICONIX BVDSS= 20V DCRON= 0.100 CRSS = 400pF Qg= 50nCD1 MOTOROLA

R2 KRL SP-1/2-A1-0R100 Pd = 0.75W


ITH

CT

GND

LTC1147-3.3

VINPDRIVE

SENSE +

SENSE

+

C50.001F

+

VIN4V TO 14V

R11k

C33300pFX7R

C4560pFNPO

2

8

5

4

Q1Si9430DY

D1MBRD330

C222F 225V

100H

R20.1

3.3V1A

C6220F 10V

QUIESCENT CURRENT = 170ATRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 170mA

1

7

SHUTDOWN6

+

L1

1

2

4

3

C10.1F

3



18/44

Application Note 54

AN54-18

LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter withSurface Mount Technology

One more application circuit with LTC1147 is presented inFigure 16A. It is optimized for 5V to 3.3V conversion with

input voltages of 4V to 8V (limited by the P-channelMOSFET). A circuit board has been laid out for this circuitand has subsequently been thoroughly tested under fulloperating conditions and optimized for mass productionrequirements. A Gerber file for the board is available uponrequest.

AN54 F16A

C1 AVX TPSD476M016R0150 TANTALUM 47F 16V

C6 AVX TPSD107M010R0100 TANTALUM 100F 10V

D1 MOTOROLA MBRS130LT3 BVR = 30V

L1 SUMIDA CDR74B-100LC 10 H

Q1 SILICONIX PMOS Si9433

R2 IRC LRC-LR2010-01-R068-F

ALL OTHER CAPACITORS CERAMIC

ITH

CT

GND

LTC1147-3.3

VINPDRIVE

SENSE +

SENSE

+

C5

0.01F+

VIN4V TO 8V

0V = NORMAL

2V = SHUTDOWN

R11k

C33300pF

C4120pF

2

8

5

4

D1MBRS130LT3

C147F16V

R20.068

VOUT3.3V1.5A

C6100F 10V

1

7

SHUTDOWN6

L1

10H

C20.1F

3

Q1P-CH

Si9433DY

Figure 16A. LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology

OUTPUT CURRENT (A)

0.001

EFFICIEN

CY(%)

100

95

90

85

80

75

70

65

600.01 0.1 1

AN54 F16B

LTC1147-3.3SUMIDA CDR74B

VIN= 5V

LTC1147-3.3SUMIDA CD54

VIN

= 5V

2

Figure 16B. LTC1147: (4V-8V to 3.3/1.5A)Buck Converter Measured Efficiency


19/44AN54-19

Application Note 54

LTC1148: (10V-14V to 5V/10A) High CurrentBuck Converter

Due to differences in physical structure between N- and P-channel MOSFETs, the former are usually more cost

effective, more available, and provide better internal pa-rameters for the same size. This is especially importantwhen high output currents are required. With 5A to 10Aoutput currents the use of N-channel MOSFETs in place ofP-channel is the most preferable solution. An implemen-tation of this idea is presented in Figure 17A.

A special Q4 gate drive circuit that uses a bootstrappingtechnique is added to provide required gate drive. Whenpin 1 goes high it turns Q3 on, providing a path for fast Q4gate capacitance discharge. With Q3 off, Q1 and Q2

saturate each other feeding positive voltage to Q4s gate.As a result Q4 turns on, and the positive pulse at its sourceis AC coupled through C6 supplying bootstrapped VCCforthe gate drive SCR. The external driver circuit contains

only inexpensive, readily available small-signal transis-tors, yet allows the use of all N-channel MOSFETs. Effi-ciency reaches 96% (see Figure 17B).

OUTPUT CURRENT (A)

0.150

EFFICIENCY(%)

70

80

90

100

1 10

AN54 F17B

60

VIN= 10V

VIN= 14V

Figure 17A. LTC1148: (10V-14V to 5V/10A) High Current Buck Converter

Figure 17B. LTC1148: (10V-14V to 5V/10A) High CurrentBuck Converter Measured Efficiency

Q4IRFZ44

AN54 F17A

C1 (Ta)

C7 UNITED CHEMI-CON (Al) LXF35VB272M16 X 40 ESR = 0.018 IRMS= 2.900AC8 NICHICON (Al) UPL1C222MRH ESR = 0.028 IRMS= 2.010AQ4, Q5 IR NMOS BVDSS= 60V DCRON= 0.028 CRSS = 310pF Qg= 69nCD1, D2 MOTOROLA SILICON VBR = 75V


ITH

CT

SGND PGND

LTC1148-5

VINPDRIVE

SENSE +

SENSE

NDRIVE

C50.001F

+

VIN10V TO 14V

C1

1F

R41k

C3

3300pFX7R

C4820pFNPO

10

4

1

8

7

14

Q5IRFZ44

D31N5818

C6

0.47F

R80.01

5V10A

C82200F 3 16V

3

11

12

SHUTDOWN

6

C2

0.1F

+

Q3VN2222LL

D11N4148

R120k

Q12N3906

Q22N2222

+ C72700F 235V

R6100

D21N4148

R3220

L1

33H

R722k

R2220

R5100


L1 COILTRONICS CTX33-10-KM DCR = 0.010Kool MCORE


QUIESCENT CURRENT = 22mA


20/44

Application Note 54

AN54-20

Two resistors are placed in series with the current sensepins. This significantly improves circuit noise immunitywhich is of great importance when switching high current.R7, connected between pin 7 and ground, disables Burst

Mode operation so that the regulator operates continuously.

LTC1149: (12V-36V to 5V/5A) High Current, HighVoltage Buck Converter

Figure 18A shows a high current, high voltage buckconverter. The LTC1149 is used to accommodate the inputvoltage requirement. As in Figure 17A the top N-channelMOSFET is driven by an external circuit which inverts thechips P-drive output and uses bootstrapping to providepositive gate-source voltage. The peak-to-peak gate volt-age is defined by the DC portion of the gate driver V CC.

Therefore, not to exceed maximum gate voltage for theMOSFET, D1s anode is connected to internal 10V regula-tor output. In this application PDRIVEpin 4 is used because

an output referenced to ground is required. PGATEpin 1provides the same drive signal referenced to VCC.

Figure 18B. LTC1149: (12V-36V to 5V/5A) High Current, HighVoltage Buck Converter Measured Efficiency

OUTPUT CURRENT (A)

0.150

EFFICIENCY(%)

70

80

90

100

1 5

AN54 F18B

60

VIN= 12V

VIN= 24V

VIN= 36V

Figure 18A. LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter

Q4MTP30N06EL

AN54 F18A

C60.001F

+

C70.22F

R70.02

5V5A

C9220F 2 10V

Q3VN2222LL

D11N4148

R210k

Q12N3906

Q2

2N2222

C81000F 63V

D21N4148

R4220

L1

50H

R3220

VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-5

PGATE

VIN

SENSE +

SENSE

NGATE

VIN12V TO 36V

C10.1F

+C21F

C30.1F

R11k

C43300pF

X7R

C5820pFNPO

3

5

16

10

15

7

6

4

9

8

13

2

11

12

14

SGND PGND

PDRIVE

RGND

Q5IRFZ34

D3MBR160

C2 (Ta)

C8 NICHICON (Al) UPL1J102MRH ESR = 0.027 IRMS= 2.370A


Q1 PNP BV CEO= 30V

Q2 NPN BVCEO= 40V

Q3 SILICONIX NMOS BVDSS= 60V RDSON= 5.000

Q4 MOTOROLA NMOS BVDSS= 60V RDSON= 0.050 CRSS = 100pF Qg= 40nC

R6100

R5100

+

1


D1, D2 SILICON VBR = 75V



L1 COILTRONICS CTX50-5-52 DCR = 0.021 #52 IRON POWDER CORE



21/44AN54-21

Application Note 54


The circuit in Figure 19A uses the same configuration butis designed to provide up to 10A output current. Besidesthe usual external component changes, the circuit useshigher current MOSFETs to improve efficiency at maxi-mum power levels. Efficiency at 5A output is severalpercentage points better than in the previous example(compare Figures 18B and 19B). R7 keeps the regulator incontinuous mode causing the rapid efficiency decrease atlighter loads.

Figure 19B. LTC1149: (12V-48V to 5V/10A) High Current,High Voltage Buck Converter Measured Efficiency

OUTPUT CURRENT (A)

0.150

EFFICIENCY(%)

70

80

90

100

1 10

AN54 F19B

60

VIN= 12V

VIN= 48V

VIN= 36V

VIN= 24V

Q4IRFZ34

AN54 F19A

C60.001F

+

C70.22F

R80.01

5V10A

Q3VN2222LL

D11N4148

R220k

Q12N3906

Q22N2222

C81000F 2 63V

D21N4148

R4220

L1

33H

R3220

VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-5

PGATE

VIN

SENSE +

SENSE

NGATE

VIN12V TO

48V

C10.1F

+C21F

C30.1F

R11k

C43300pF

X7R

C5820pFNPO

3

5

16

10

15

7

6

1

4

9

8

13

2

11

12

14

SGND PGND

PDRIVE

RGND

Q5IRFZ44

D3MBR160

C2 (Ta)

C8 NICHICON (Al) UPL1J102MRH ESR = 0.027 IRMS= 2.370A

C9 NICHICON (Al) UPL1C222MRH ESR = 0.028 IRMS= 2.010A

Q1 PNP BVCEO= 30V

Q2 NPN BVCEO= 40V

Q3 SILICONIX NMOS BVDSS= 60V RDSON= 5.000



R6100

R5100

+

R722k


+

C9220F 3 16V

D1, D2 SILICON VBR = 75V







22/44

Application Note 54

AN54-22


9

8

Q4

IRFZ44

AN54 F20A

C70.001F

C70.22F

24V10A

C101000F 3 35V

Q3VN2222LL

D1IN4148

R320k

Q12N5087

Q2MPS651

C81000F 2 63V

D21N4148

R25.1k

L1

50H

VCC

VCC

CAP

SD2

ITH

CT

LTC1149

PGATE

VIN

VFB

SENSE +

NGATE

VIN32V TO 48V

C10.1F

+ C21F

C30.1F

R11k

C43300pF

X7R

C5270pFNPO

3

5

16

15

7

6

4

10

13

2

11

12

14

SGND PGND

PDRIVE

RGND

Q5IRFZ44

C2 (Ta)C9 NICHICON (Al) UPL1J102MRH ESR = 0.027 IRMS= 2.370A

C10 NICHICON (Al) UPL1V102MRH ESR = 0.029 IRMS= 1.980A

Q4, Q5 IR NMOS BVDSS= 60V RDSON= 0.028 CRSS = 310pF Qg= 69nC

Q1 PNP BVCEO= 50V

Q2 NPN BVCEO= 60V

D1, D2, D3, D4 SILICON VBR = 75V





100

R6100

+

SENSE

1

C6100pF

R8220k1%

R5220

D31N4148

R4220

D41N4148

R912k1%

D5MBR160

R100.01

R7

VOUT= 1.25V (1 + R8/R9)


TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 1.5A

+

+

R1139k


If an output voltage other than 5V or 3.3V is required, anadjustable version of the regulator must be used. A 24V/10A example is shown in Figure 20A. The output voltageis set by resistors R8 and R9. The LTC1149 monitors VFB(pin 10) keeping it at 1.25V. Similar to the previous twocircuits, an external gate driver is added to switch theN-channel MOSFET Q2. To ensure consistent start-up ofthe bootstrapping circuitry, the driver is initially poweredby R2 and D2. (The main requirement at start-up is tosupply the driver with VCC that exceeds output targetvoltage.) After the switching starts, D1 an D3 power theexternal gate drive circuit.

OUTPUT CURRENT (mA)

1050

EFFICIEN

CY(%)

70

80

90

100

100 1A 10A

AN54 F20B

60

VIN= 32V

VIN= 45V

Figure 20B. LTC1149: (32V-48V to 24V/10A) High Current,High Voltage Buck Converter Measured Efficiency


23/44AN54-23

Application Note 54

LT1148: (4V-14V to 5V/1A) SEPIC Converter

Figure 21A provides the function of a step-up and step-down converter without using a transformer. This topol-ogy is called a SEPIC converter. The P-channel transistorand L1 are arranged similarly to a buck-boost topologyproviding the boost part of the regulator. Pulses at Q2sdrain (actually two paralleled devices) are coupled via C8to the buck portion that includes Q3 and L2. This circuitaccepts 4V to 14V input and provides a solid 5V output.Even though the schematic shows two inductors, theycarry the same current and can be wound on a single core.Such dual coils are readily available (see circuit parts list).This topology is acceptable for moderate loads only, as thecoupling capacitor C8 carries the full load current and

must be sized accordingly. When the sense resistor isplaced at ground potential, such as the case in this circuit,the off-time increases approximately 40%.

An adjustable version of the regulator is required when the

OUTPUT CURRENT (A)0.001

50

EFFICIENCY(%)

70

80

90

100

0.01 0.1 1

AN54 F21B

60

VIN= 14V

VIN= 4V

VIN= 5V

VIN= 4V

VIN= 10V

VIN= 5V

current sense resistor is placed at ground. This allows toprovide different output voltages. D2 is included for foldbackshort-circuit protection. When VOUTequals zero (output isshorted) D2 clamps pin 6 and limits the output current.

Figure 21B. LTC1148: (4V-14V to 5V/1A)Buck-Boost Converter Measured Efficiency

Figure 21A. LTC1148: (4V-14V to 5V/1A) SEPIC Converter

AN54 F21A

C60.1F

VOUT5V

1A

C10220F 10V

Q2Si9430DY x 2

C7100F20V

VIN4V TO14V C1

1F

C20.1F

R11k

C43300pF

X7R

C5390pFNPO

5

10

6

4

1

9

8

7

D2MBR0520L

14

3

11

12

D11N5818

C1 (Ta)


C8, C10 SANYO (OS-CON) 10SA220M ESR = 0.035 IRMS= 2.360A





L1 COILTRONICS CTX50-4P, CTX50-5P


+

R20.082

TO VOUT

SHUTDOWN

ITH

CT

LTC1148

PDRIVE

VIN

SENSE +

NDRIVESGND PGND

VFB

SENSE

INT VCC

C8220F10V

L150H

Q3Si9410DY

R375k1%

R425k1%

+

C9100pF

++

L250H

VOUT= 1.25V (1 + R3/R4)


TRANSITION CURRENT (Burst Mode OPERATION/

CONTINUOUS OPERATION) = 250mA/VIN= 5V


24/44

Application Note 54

AN54-24

OUTPUT CURRENT (A)

0.00150

EFFICIEN

CY(%)

70

80

90

100

0.01 0.1 0.5

AN54 F22B

60

VIN= 14VVIN= 4V

VIN= 10VVIN= 5V

LTC1148: (4V-14V to 5V/0.5A, 5V/0.5A)Split Supply Converter

Applications requiring a split supply can use the circuitpresented in Figure 22A. It contains the converter from

Figure 21A and adds a synchronous charge pump Q4 toprovide a 5V output. Q4 source is referenced to the 5Vline, and its gate drive is AC coupled via C11 and clampedby D3. The outputs exhibit excellent tracking with line andload changes. This is a great way to build a dual outputconverter without any transformer.

SENSE

AN54 F22A

C70.1F

C10220F 10V

Q2Si9430DY

C8100F20V

VIN4V TO14V C1

1F

C20.1F

R11k

C43300pF

X7R

C5390pFNPO

5

10

6

4

1

8

7

9

14

3

11

12

D11N5818

C1 (Ta)

C8 SANYO (OS-CON) 20SA100M ESR = 0.037 IRMS= 2.250AC9, C10, C12 SANYO (OS-CON) 10SA220M ESR = 0.035 IRMS= 2.360AQ2 SILICONIX PMOS BVDSS= 20V RDSON= 0.100 CRSS = 400pF Qg= 50nCQ3, Q4 SILICONIX NMOS BVDSS= 30V RDSON= 0.050 CRSS = 160pF Qg= 30nCD1, D2 MOTOROLA SCHOTTKY VBR = 30V


L1 COILTRONICS CTX50-4

+

R20.05

VOUT

SHUTDOWN

ITH

CT

LTC1148

PDRIVE

VIN

SENSE +

NDRIVESGND PGND

VFB

INT VCC

C9220F10V

L150H

Q3Si9410DY

R375k1%

R425k1%

C110.22F

++

L250H

VOUT= 1.25V (1 + R3/R4)

QUIESCENT CURRENT = 250A TRANSITION CURRENT (DIS/CONT) = 130mA/VIN= 5V

C6100pF

R551k

D31N4148

C12220F 10V

VOUT5V0.5A

+VOUT5V0.5A

+

+

Q4Si9410DY

D2

1N5818

D4MBR0520L

Figure 22A. LTC1148: (4V-14V to 5V/0.5A, 5V/0.5A) Split Supply Converter

Figure 22B. LTC1148: (4V-14V to 5V/0.5A, 5V/0.5A)Split Supply Converter Measured Efficiency


25/44AN54-25

Application Note 54

LTC1148: (4V-10V to 5V/1A) Positive-to-NegativeConverter

Figure 23A shows a buck-boost converter using theLTC1148. This is an inverting topology, and it can inher-ently buck or boost the input voltage. Ground pins of thechip are referenced to the output line; no additional levelshifting circuit is required to drive the N-channel FET Q3(its source is referenced to 5V as well). Now even withminimum input level, the circuit provides a solid 9V peak-to-peak MOSFET drive signal. However, so as not toexceed absolute maximum voltage at pin 3, the input lineis limited to 10V. If the circuit is required to accept a higherinput voltage, the LTC1148HV can be used instead. Q1 isadded to provide a logic level shutdown feature. If shut-down is not needed omit Q1 and R1, and short pin 10 topin 11.

Figure 23A. LTC1148: (4V-10V to 5V/1A) Positive-to-Negative Converter

OUTPUT CURRENT (A)

0.001

EFFICIEN

CY(%)

100

95

90

85

80

75

70

65

600.01 0.1

AN54 F23B

1 10

4V TO 5V/1A

10V TO 5V/1A

Figure 23B. LTC1148: (4V-10V to 5V/1A)Positive-to-Negative Converter MeasuredEfficiency

SENSE

AN54 F23A

C50.01F

C8220F 210V

Q2Si9430DY

C7150F 216V

VIN4V TO10V

C11F

C20.1F

R21k

C36800pF

X7R

C4560pFNPO

5

10

6

4

1

8

7

914

3

11

12

D11N5818

C1 (Ta)

C7 SANYO (OS-CON) 16SA150M ESR = 0.035 IRMS= 2.280AC8 SANYO (OS-CON) 10SA220M ESR = 0.035 IRMS= 2.360AQ2 SILICONIX PMOS BVDSS= 20V RDSON= 0.100 CRSS = 400pF Qg= 50nCQ3 SILICONIX NMOS BVDSS= 30V RDSON= 0.050 CRSS = 160pF Qg= 30nCD1 MOTOROLA SCHOTTKY VBR = 30V

R2 KRL NP-1A-C1-0R050J



+

R20.05

Q1TP0610L

SHUTDOWN

ITH

CT

LTC1148

PDRIVE

VIN

SENSE +

NDRIVESGND PGND

VFB

INT VCC

L150H

Q3Si9410DY

R375k1%

R425k1%

+

VOUT= 1.25V (1 + R3/R4)

C6200pF

5V1A

+R11M

SHUTDOWN


26/44

Application Note 54

AN54-26

LTC1148: (5V-12V to 15V/0.5A) Buck-BoostConverter

Figure 24A presents an inverting regulator designed toaccommodate higher output voltages. The LTC1148 can-

not accept feedback directly from a negative output. Toregulate negative outputs, the feedback must be invertedand compared against 1.25V. This function is provided bya DC level shifting amplifier consisting of Q1 and associ-ated components. Resistor R4 provides amplifier negativefeedback, effectively cancelling variations in VCC, and Q2provides temperature compensation. The output voltageis set by resistors R4 and R5. As usual, with the senseresistor at ground potential, the off-time increases roughlyby 40%.

OUTPUT CURRENT (A)

0.001

EFFICIENCY(%)

95

90

85

80

75

70

650.01 0.1 1

AN54 F24B

5V TO 15V/0.5A

12V TO 15V/0.5A

Figure 24B. LTC1148: (5V-12V to 15V/0.5A)Buck-Boost Converter Measured Efficiency

AN54 F24A

C80.01F

C947F25V

Q3Si9435DY2

C7220F10V

C6200pF

C56800pF

10

6

4

11

1

8

7

9

12

3

U1

D3MBR735

R7 DALE LVR-3 0.033WL1 COILTRONICS CTX50-5-52C7 SANYO OS-CON 105A220KC9, C10 SANYO OS-CON 255C47K

+

R70.033

Q22N5210

Q12N5210

LTC1148

VIN

SHUTDOWN

ITH

CT

SGND

PDRIVE

SENSE+

SENSE

VFB

PGND

L150H

R449.9k1%

+

+ C1047F25V

C20.1F

C31F

C11200pF

R61k

R356k

> 1.5V = SHUTDOWN

R5634k1%

VOUT15V0.5A

VIN5V TO 12V

+

Figure 24A. LTC1148: (5V-12V to 15V/0.5A) Buck-Boost Converter


27/44AN54-27

Application Note 54

LTC1148: (2V-5V to 5V/1A) Boost Converter

Even though the LTC1148 is mainly used in step-downconverters, it can also show excellent performance in theboost configuration. A boost implementation is shown in

Figure 25A. This is a two-cell to 5V converter that uses theLT1109 to provide 12V to power the main regulator chip(unfortunately, MOSFETs do not operate with only 2V at thegate). The LT1109 is a small micropower IC that requiresonly three external components and provides great effi-ciency. An N-channel transistor is used as the switch, andgeneral purpose MOSFETs Q1 and Q2 are used to form aninverting gate driver. When Q3 turns off, the voltage at itsdrain rises above VIN, and a Schottky diode D2 startsconducting. In a short period of time Q4 shorts it outproviding a synchronous rectification feature and increas-ing efficiency. If 12V is already available, the LT1109 can beomitted and the 12V line connected directly to pin 3.

Figure 25A. LTC1148: (2V-5V to 5V/1A) Boost Converter

Q1TP0610L

SENSE

AN54 F25A

C60.001F

C8220F 210V

VIN2V TO5V

C1100F10V

R21k

C46800pF

X7R

C5390pFNPO

10

6

4

1

12V

8

7

9

14

3

11

12

D21N5818

C1 SANYO (OS-CON) 10SA100M ESR = 0.045 IRMS= 1.870AC3 (Ta)

C8 SANYO (OS-CON) 10SA220M ESR = 0.035 IRMS= 2.360AQ3, Q4 SILICONIX NMOS BVDSS= 30V RDSON= 0.050 CRSS = 160pF Qg= 30nCD1, D2 MOTOROLA SCHOTTKY VBR = 30V

SHUTDOWN

ITH

CT

LT1109

PDRIVE

VIN

SENSE +

NDRIVESGND PGND

VFB

L133H

Q2VN2222LL

R375k1%

+

C7100pF

5V1A

R10.05

VIN

SENSE

GND

S/D7

3

1

4

8

D11N5818

SHUTDOWN

C20.1F

C31F

+

Q3Si9410

L225H

R425k1%

Q4Si9410

+

SW

LTC1148

VR1


L1 COILTRONICS CTX33-1 DCR = 0.220Kool MCOREL2 COILTRONICS CTX25-4

VOUT= 1.25V (1 + R3/R4)

Figure 25B. LTC1148: (2V-5V to 5V/1A)Boost Converter Measured Efficiency

OUTPUT CURRENT (A)

0.001

EFFICIENC

Y(%)

100

95

90

85

80

75

70

650.01 0.1 1

AN54 F25B

4V TO 5V/1A

2V TO 5V/1A


28/44

Application Note 54

AN54-28

LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A)Dual Buck Converter

A circuit that provides dual 3.3V/5V output is shown inFigure 26A. It uses a dual LTC1143 regulator that com-

bines two LTC1147, non-synchronous switching regula-tors. The efficiency was measured with only one outputloaded which provided worse results for low output cur-rent due to the presence of the second halfs quiescentcurrent. This circuit provides very simple means to powerdual voltage logic. It occupies small amount of boardspace and is very efficient! OUTPUT CURRENT (A)

0.001

EFFICIENC

Y(%)

95

90

85

80

75

70

65

600.01 0.1

AN54 F26B

1 10

14V TO 3.3V

8V TO 5V

8V TO 3.3V

14V TO 5V

Figure 26B. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A)Dual Buck Converter Measured Efficiency

+

+ +

PDRIVE3

SENSE+ 3

SENSE 3

GND3 GND5CT3 ITH3 ITH5 CT5

SENSE 5

SENSE+ 5

PDRIVE5

VIN3 SHUTDOWN 5 VIN5

LTC1143

CT5200pF

CT3390pF

3 14 15 7 6 11

RC51k

CC33300pF

CC53300pF

RC31k

13 10 5

12

9

8

4

1

16

VOUT55V/2A

COUT5220F10V 2

RSENSE50.05

L220H

D2MBRD330

RSENSE: KRL SL-1R050J L1, L2: COILTRONICS CTX20-4

CIN3,CIN5: AVX (Ta) TPSD226K025R0200

COUT3,COUT5: AVX (Ta) TPSE227K010R0080Q1, Q2: SILICONIX PMOS Si9430DY

D1MBRD330

0V = NORMAL>1.5V = SHUTDOWN

CIN522F25V 2

CIN322F25V 2 Q1

P-CHSi9430DY

COUT3220F10V2

L120H

RSENSE30.05VOUT3

3.3V/2A

VIN5.2V TO 14V

+

Q2P-CH

Si9430DY

0.01F 0.01F

AN54 F26A

0.22F0.22F

SHUTDOWN 3

2

Figure 26A. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter


29/44AN54-29

Application Note 54

Figure 27B. LTC1148HV-5: (5.2V-18V to 5V/1A) HighVoltage Buck Converter Measured Efficiency

LTC1148HV-5: (5.2V-18V to 5V/1A) High VoltageBuck Converter

The standard LTC1148 input voltage is limited to 16Vabsolute maximum level, which is not sufficient in some

applications. Figure 27A shows a step-down regulatorusing the high voltage LTC1148HV. It contains the sameinternal functions but accepts up to 20V input (remember,MOSFETs gates are usually rated at 20V maximum). As abuilding block it can be used in the same manner asLTC1148. Input tantalum capacitors now have to be ratedat 35V to ensure reliable operation under maximum inputvoltage.

OUTPUT CURRENT (A)

0.001

EFFICIENCY(%)

100

95

90

85

80

75

70

65

60

550.01 0.1 1

AN54 F27B

7V TO 5V

12V TO 5V

18V TO 5V

1

2

3

4

5

6

7

14

13

12

11

10

9

8

PDRIVE

NC

VIN

CT

INT VCC

ITH

SENSE

NDRIVE

NC

PGND

SGND

SHUTDOWN

NC

SENSE+

LTC1148HV-5

+ 1F

1000pFR10.1

SHUTDOWN

L150H

Q2, Si9410DY

D1MBRS140T3

Q1Si9430DY

+ CIN10F35V2

VIN5.2V TO 18V

+

COUT220F10VAVX

VOUT5V/1A

CC3300pF

RC1k

CT220pF

CINCOUTL1

R1Q1Q2

AVX (Ta) TPSD106K035R0300AVX (Ta) TPSE227K010R0080COILTRONICS CTX50-4

KRL SP-1/2-A1-0R100SILICONIX PMOS Si9430DYSILICONIX NMOS Si9410DY

AN54 F27A

Figure 27A. LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter


30/44

Application Note 54

AN54-30

OUTPUT CURRENT (A)

0.001

EFFICIENCY(%)

100

95

90

85

80

75

70

65

600.01 0.1 1

AN54 F28B

18V to 3.3V

4V to 3.3V

12V to 3.3V

Figure 28B. LTC1148HV-3.3: (4V-18V TO 3.3V/1A)High Voltage Buck Converter Measured Efficiency

LTC1148HV-3.3 (4V-18V to 3.3V/1A) High VoltageBuck Converter

Figure 28A: Here is a high voltage version of the circuitshown in Figure 4A with input voltage increased to 18V.

1

2

3

4

5

6

7

14

13

12

11

10

9

8

PDRIVE

NC

VIN

CT

INT VCC

ITH

SENSE

NDRIVE

NC

PGND

SGND

SHUTDOWN

NC

SENSE+

LTC1148HV-3.3

+ 1F

1000pF 0.1

SHUTDOWN

L150H

Q2, Si9410DY

D1MBRS140T3

Q1Si9430DY

+ CIN22F35V2

VIN4V TO 18V

+

COUT220F10V

VOUT3.3V/1A

CC3300pF

RC1k

CT270pF

CINCOUTL1R1

Q1Q2

AVX (Ta) TPSE226K035R0300AVX (Ta) TPSE227K010R0080COILTRONICS CTX50-4 Kool MCOREIRC LR2010-01-R100-G

SILICONIX PMOS Si9430DYSILICONIX NMOS Si9410DY

AN54 F28A

Figure 28A. LTC1148HV-3.3: (4V-18V to 3.3V/1A)High Voltage Buck Converter


31/44AN54-31

Application Note 54

LTC1148HV: (12.5V-18V to 12V/2A) High VoltageBuck Converter

Figure 29A is another application of the LTC1148HV whichis configured as a step-down converter to provide 12V/2A

output. With this low dropout regulator, the input can goas low as 12.5V and still produce a regulated output.Resistors R2 and R3 set the output voltage level.

OUTPUT CURRENT (A)

0.001

EFFICIENCY(%)

100

95

90

85

80

75

70

65

600.01 0.1

AN54 F29B

1 10

Figure 29B. LTC1148HV: (16V to 12V/2A) High VoltageBuck Converter Measured Efficiency

C1 (Ta)

C7 SANYO (OS-CON) 16SA150M

Q1 SILICONIX PMOS BVDSS= 20V RDSON= 0.100 CRSS = 400pF Qg= 50nCQ2 SILICONIX NMOS BVDSS= 30V RDSON= 0.050 CRSS = 160pF Qg= 30nCD1 MOTOROLA SCHOTTKY VBR = 40V


L1 COILTRONICS CTX47-5P

ITH

CT

LTC1148HV

VIN

SENSE +

SENSE

+

C60.01F

100pF

+

VIN12.5V

TO 18V

C11F

R11k

C43300pFX7R

C5150pFNPO

10

4

1

8

7

9

14

Q1Si9430DY

Q2Si9410DY

D1MBRS140T3

C322F x 235V

47H

R20.05

432k

1%

12V2A

C7150F 3 16V

3

11

12

SHUTDOWN

6

C20.1F

+

AN54 F29A

SGND PGND

PDRIVE

VFB

NDRIVE

49.9k1%

Figure 29A. LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter


32/44

Application Note 54

AN54-32

Figure

30A.

LTC1142:(6.

5V-14Vt

o

3.

3V/2A,

5V/2A,

12V/0.

15A)Triple

OutputBuckConverter

AN54

F30A

2

SHUTDOWN3

25

CT3

27

ITH3

26

INTVCC3

16

SHUTDOWN5

11

CT5

13

ITH5

12

INTVCC5

5

NC

4

PGND3

22

NC

23

PDRIVE3

7

NC

6

NDRIVE3

1

SENSE+3

28

SENSE3

9

PDRIVE5

21

NC

20

NDRIVE5

15

SENSE+5

14

SENSE5

8

NC

18

PGND5

19

NC

SGND3

SGND5

VIN5

VIN3 1

7

3

24

10

LTC1142

C4

3300pF R

8

510

C17

200pF

50V

C1

3300pF

R7

510

C16

390pF

50V

C14

1

F

50V

C15

1

F

50V

C19

1000pF

R5

18k

SHDN

4

NC4

6

NC6

7

NC7

VOUT

ADJ

21

5

VIN

GND

LT1121CS8

C10

20pF

R3649

k

1% R4294

k

1%

Q1

VN7002

1 2

3

38

C9

22

F

25V

+

Q3

Si9410DY

D2

MBRS140+

C6

22

F

25V

+

C7

22

F

25V

R2

100

R1

100

R10

0.0

40

+

C20

220

F

10V

+

C21

220

F

10V

10

9

8

7

1

2

3

4

D3

MBRS140R

622

C13

1000pF

C5

0.1

F

30

H,

2A

LPE-6562-A

026

+

C8

22

F

35V

Q5

Si9410DY

D1

MBRS14

0+

C2

22

F25V

+

C3

22

F

25V

3

2

4

1

L133

H

2ACTX

33-4

+

C11

100

F

10V

R9

0.0

50

+

C12

100

F

10V

+

+

12VENABLE

VIN

SHUTDOWN

(TTLINPUT)

SHUTDOWN

(TTLINPUT)

+VIN

6.5

VTO14V

Q4

Si9430DY

Q2

Si9430DY 4

0V=

12VOFF

>3V=

12VON

(6VMAX)

DONOTFLOAT

C18

2

200pF

T1

6 51.8

TSHUTDOWNPINS2AND16MUSTACTIVELYBEDRIVEN

EITHERHIGHORLOW

ANDNOT

ALLOWEDTOFLOAT

.

+

3.3

V/2A

12V/150mA

C2

,C3

,C6

,C7,

C9

C11

,C12

C20

,C21

L1

AVX(Ta)TPSD226M025R0

200

AVX(Ta)TPSD107K010R0100

AVX(Ta)TPSE227M010R0

100

COILTRONICSCTX33-4

R9

R10

T1

IRCLR2512-R

050

IRCLR2512-R

040

DALE

,LPE-6562-A

O26

5V/2A


33/44AN54-33

Application Note 54

LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A)Triple Output Buck Converter

LTC1142 is a dual output synchronous switching regula-tor controller. Two independent controller blocks

(LTC1148-based) simultaneously provide 3.3V and 5Voutputs. The circuit in Figure 30A shows an application ofthis IC; it generates triple output voltages with 12V forflash memory programming in addition to the usual logicpower levels. The 3.3V section is a regular buck convertercircuit, the 5V section contains an off-the-shelf trans-former T1 in place of the inductor. The secondary windingis used to boost the output level which is rectified andregulated by an LT1121 to provide a clean and stable 12Voutput. A turns ratio of 1:1.8 is used to ensure that theinput voltage to the LT1121 is high enough to keep theregulator out of dropout. With LTC1142 synchronousswitching, the auxiliary 12V output may be loaded withoutregard to the 5V primary output load as long as the loopremains in continuous operation mode. Continuous op-eration is ensured by R5 which inhibits Burst Modewhenever the 12V output is enabled (enable line goeshigh). Make sure that the enable lines are not floating andare driven by TTL level signals. A circuit board has beenlaid out for this circuit and has subsequently been thor-oughly tested under full operating conditions and opti-mized for mass production requirements. A Gerber file forthe board is available upon request.

OUTPUT CURRENT (A)

0.00160

EFFICIENCY(%)

65

100

0.01 2.5

AN54 F30B

0.1

80

1

90

70

75

85

95

LTC1142-3.3VIN= 8V

LTC1142-5VIN= 8V

Figure 30B. LTC1142:(6.5V-14V to 3.3V/2A, 5V/2A,12V/0.15A) Triple Output Buck ConverterMeasured Efficiency


34/44

Application Note 54

AN54-34

LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A)High Voltage Triple Output Buck Converter

Figure 31A shows the same configuration as Figure 30Ausing the high voltage LTC1142HV. Circuit operation isidentical, but now it can accept up to 18V at the input.

OUTPUT CURRENT (A)

0.00160

EFFICIENC

Y(%)

65

100

0.01 2.5

AN54 F30B

0.1

80

1

90

70

75

85

95

LTC1142-3.3VIN= 8V

LTC1142-5VIN= 8V

Figure 31B. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A,12V/0.15A) Measured Efficiency

Figure 31A. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter

+

+ +

1000pF

PDRIVE3

SENSE+3

SENSE3

NDRIVE3

PGND3 SGND3 CT3 ITH3 ITH5 CT5 SGND5 PGND5

NDRIVE5

SENSE5

SENSE+5

PDRIVE5

VIN3 SHUTDOWN 3 SHUTDOWN 5 VIN5

LTC1142HV

CT5200pF

4 3 25 27 13 11 17 18

510

3300pF 3300pFCT3390pF

510

1F

224 16 10

9

15

14

20

23

1

28

6

VOUT55V/2A

C4220F

10V 2

22F35V

RSENSE50.04

1.8T30H

D2MBRS140

Q3Si9410DY

0V = NORMAL>1.5V = SHUTDOWN

1F

C222F25V 2

C122F25V 2

VIN6.5V TO18V

Q4Si9430DY

Q5Si9410DY

D1MBRS140

C3100F10V 2

L133H

RSENSE30.05VOUT3

3.3V/2A

AN54F31A

++

Q2Si9430DY

2000pF

C1, C2C3, C4L1RSENSE3RSENSE5T1

AVX (Ta) TPS226K035R0300AVX (Ta) TPSD227K010R0100COILTRONICS CTX33-4KRL SL-C1-1/2-0R050JKRL SL-C1-1/2-0R040JDALE LPE-6562-A026 PRIMARY: SECONDARY = 1:1.8

22

R1100

T1

12V ENABLE0V = 12V OFF>3V = 12V ON

(6V MAX)

1000pF

D3MBRS140

R3660k

R4300k

20pF+

22F25V

12V/150mA

LT1121

VOUT

SHUTDOWN

VIN

ADJ

R2100

Q1VN7002

R518k

+

GND

+


35/44AN54-35

Application Note 54

LTC1148: High Efficiency Charger Circuit

The LTC1148 regulator can be used as a highly efficientbattery charging device. Figure 32 shows a circuit that isprogrammable for 1.3A fast charge or 100mA tricklecharge mode. During the fast charge interval, the resistordivider network (R4 and R5) forces the LTC1148 feedbackpin below 1.25V causing the regulator to operate at themaximum output current. Sense resistor R3 controls thecurrent at approximately 1.3A. When the batteries aredisconnected, the error amplifier sets the output voltage tobe 8.1V (for proper operation this voltage should exceed

maximum possible voltage across the battery pack). Di-ode D2 prevents the batteries from discharging throughthe divider network when the charger is shut down.

Dual rate charging is controlled by Q3 which selects

between fast and trickle charge. When the transistor turnson, R1 limits error amplifier output so that the currentlimiter starts operating at 100mA. If the trickle chargecurrent needs to be altered, adjust R1. With 1.3A outputcurrent, this charger is capable of efficiency in excess of90% which minimizes power dissipated in surface mountcomponents.

C1 (Ta)

C3 AVX (Ta) TPSD226K025R0100 ESR = 0.100 I RMS= 0.775A

C8 AVX (Ta) TPSE227M010R0100 ESR = 0.100I RMS= 1.149A

Q1 SILICONIX PMOS BV DSS= 20V RDSON= 0.125 CRSS = 400pF Qg= 25nC JA= 50C/WQ2 SILICONIX NMOS BV DSS= 30V RDSON= 0.050 CRSS = 160pF Qg= 50nC JA= 50C/WD1, D2 MOTOROLA SCHOTTKY VBR = 40V

R3 KRL SP-1/2-A1-0R100J Pd = 0.75V

L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M CORE


VOUT= 1.25V (1 + R4/R5) = 8.1V

FAST CHARGE = 130mV/R3 = 1.3A

TRICKLE CHARGE = 100mA

EFFICIENCY > 90%

ITH

CT

LTC1148

VIN

SENSE +

SENSE

+

C60.01F

C7100pF

+

VIN8V TO

15VC11F

R2

1k

R1

51

C43300pFX7R

C5200pFNPO

10

0V = NORMAL> 1.5A = SHUTDOWN

4

1

8

7

9

14

Q1Si9430DY

Q2Si9410DY

D1MBRS140T3

D2MBRS340T3

C322F 235V

R30.1

R4274k

1%

VOUT

C8220F 10V

3

11

12

Q3VN2222LL

1TRICKLECHARGE

SHUTDOWN

6

C20.1F

+

L150H

1

2

4

3

AN54 F32

SGND PGND

PDRIVE

VFB

NDRIVE

VBAT4 CELLS

R549.9k1%

Figure 32. LTC1148: High Efficiency Charger Circuit


36/44

Application Note 54

AN54-36

LTC1148: High Voltage Charger Circuit

Figure 33 is a variation of Figure 32. It is designed tocharge 6 cells and uses the LTC1148HV for higher inputvoltages. R4 value has been changed to provide 12.3V

output when the battery is not connected.

C1 (Ta)

C3 AVX (Ta) TPSD226K035R0200 ESR = 0.200 I RMS= 0.663A

C8 AVX (Ta) TPSE107M016R0100 ESR = 0.100I RMS= 1.149A

Q1 SILICONIX PMOS BV DSS= 20V RDSON= 0.125 CRSS = 400pF Qg= 25nC JA= 50C/WQ2 SILICONIX NMOS BV DSS= 30V RDSON= 0.050 CRSS = 160pF Qg= 50nC JA= 50C/W

D1, D2 MOTOROLA SCHOTTKY VBR = 40V

R3 KRL SP-1/2-A1-0R100J Pd = 0.75V

L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M CORE


VOUT= 1.25V (1 + R4/R5) = 12.3V

FAST CHARGE = 120mV/R3 = 1.3A

TRICKLE CHARGE = 100mA

EFFICIENCY > 90%

ITH

CT

LTC1148HV

VIN

SENSE+

SENSE

+

C60.01F

C7100pF

+

VIN12V TO

18VC11F

R21k

R151

C43300pFX7R

C5200pFNPO

10

0V = NORMAL> 1.5A = SHUTDOWN

4

1

8

7

9

14

Q1Si9430DY

Q2Si9410DY

D1MBRS140T3

D2MBRS340T3

C322F 235V

R30.1

R4442k1%

VOUT

C8100F 16V2

3

11

12

Q3VN2222LL

1TRICKLECHARGE

SHUTDOWN

6

C20.1F

+

L150H

1

2

4

3

AN54 F33

SGND PGND

PDRIVE

VFB

NDRIVE

VBAT6 CELLS

R549.9k1%

Figure 33. LTC1148: High Voltage Charger Circuit


37/44AN54-37

Application Note 54

LTC1142A: High Efficiency Power Supply Providing3.3V/2A with Built-In Battery Charger

Figure 34 implements a high efficiency step-down con-verter with a built-in battery charger using a single IC. Onesection of the dual LTC1142A is used to convert 4-cells to

3.3V/2A in a regular buck configuration. The other sectionis configured in the same way as the battery charger fromFigure 32. It is powered from a wall adapter and providesthe battery with fast or trickle charging rate. When the

adapter is not connected, D3 prevents the battery fromdischarging through the R2/R1 divider network.

Figure 34. LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger

1000pF

+

+

+

1000pF

PDRIVE1

SENSE+1

SENSE1

NDRIVE1

PGND1 SGND1 CT1 ITH1 ITH2 CT2 SGND2 PGND2

NDRIVE2

SENSE2

VFB2VFB1

SENSE+2

PDRIVE2VIN1 SHUTDOWN 1 SHUTDOWN 2 VIN2

LTC1142A

CT2330pF

5 4 25 27 13 11 18 19

RC21k

RX51

CC13300pF

CC23300pF

CT1200pF

RC11k

0.22F

324 17

100pF 100pF

10

9

15

14

16

20

23

1

28

2

6

VOUT23.3V/2A

VBATT4 CELLSNiCAD

COUT2220F10V 2

RSENSE20.05

P-CHSi9433DY

L225H

D2MBRS140T3

N-CHSi9410DY

0.22F

CIN222F25V 2

CIN122F35V 2

P-CHSi9430DY

N-CHSi9410DY

D1MBRS140T3

D3MBRS340T3

COUT1220F

10V

L150H

RSENSE10.1

R2274k

1%

R484.5k1%

R351k1%

R149.9k

1%

VIN8V TO 18V

FROM WALL ADAPTER0V = CHARGE ON

>1.5V = CHARGE OFF0V = OUTPUT ON

>1.5V = 3.3V OUTPUT OFF

L1L2RSENSE1RSENSE2

COILTRONICS CTX50-4COILTRONICS CTX25-4KRL SL-C1-1/2-1R100J KRL SL-C1-1/2-1R050J

FAST CHARGE = 130mV/RSENSE1= 1.3ATRICKLE CHARGE = 130mV/RSENSE1= 100mA AN54 F34

+

1 FOR TRICKLE CHARGE

VN2222LL


38/44

Application Note 54

AN54-38

LTC1149: Dual Output Buck Converter

The circuit shown in Figure 35A implements the mostelegant approach for dual output regulators that provide3.3V and 5V outputs. It uses a single LTC1149. The

synchronous rectification feature of this chip is used toprovide excellent efficiency, as well as good cross regula-tion between the two outputs. Maximum output power ofthe converter is 17W, which may be drawn in any combi-nation between 3.3V and 5V outputs.

A regular buck regulator is used for producing 3.3V outputwith T1s primary in place of the buck inductor. Thesecondary of T1 forms a boost winding for 5V output. Thetransformer is wound with a simple trifilar winding toensure that the primary is closely coupled to the second-

ary. Superior cross regulation is achieved by the closeprimary-to-secondary coupling and by splitting voltagefeedback paths (resistors R1 and R2 provide feedbacksignals from both 3.3V and 5V outputs). Diodes D1, D2and capacitor C7 comprise a soft-start circuit that causesthe output voltage to increase slowly when the power isfirst applied to the circuit. This circuit prevents overshoot

at the 3.3V output. The transformer used in this exampleis a standard product (see the parts list). A circuit boardhas been laid out for this circuit and has subsequentlybeen thoroughly tested under full operating conditions

and optimized for mass production requirements. A Ger-ber file for the board is available upon request.

Figure 35A. Single LTC1149: Dual Output Buck Converter

VINS/D1/VFB

S/D2

CT

ITH

VO(REG)

VI(REG)

CAP

PGATE

PDRIVE

NGATE

SENSE+

SENSE

RGNDPGND SGND

LTC1149

10

15

6

7

3

5

16

C1256pF

C132.2F

12 14 11

1

4

13

9

8

R524.9k

1%R41k

C80.068F

C3, C4, C15, C16C5, C6, C8, C17R3T1

AVX (Ta) TPSE227M010R 49BCPAAVX (Ta) TPSE226M035R 49BCPAIRC LR512-01-R020FHURRICANE, HL-8700

C102200pF

C111000pF

2

C190.1F

D3

BAS16

C90.047F

C141000pF

D1BAS16

C710F

QP1Si9435DY

R6100

R7100

C201F

4 QP2Si9435DY

+

1

43

6

TP1

5

2

T1HL-8700

VIN

VIN6V TO

24V +C5

22F

+C6

22F

+C17

22F

+C18

22F

R1102k1%

4

R833k

D6BAS16

QN1Si9410DY

D4MBRS140

QN2Si9410DY

+C1220F +C2

220F

+C15220F +C16

220F

+C3220F

D2

BAS16

R2124k1%

+C4220F

VOUT

3.3VOUT

5VOUT

BOLD LINES INDICATE HIGH CURRENT PATHS (SHORT LEADS)

R30.02

D5MBRS140

AN54 F35A

11 T11 T

11 T

Figure 35B. LTC1149: Du

An54af ci Linear Reguladores

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