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Shrink Battery-Powered Products with a Combination BatteryCharger and DC/DC Converter Design Note 1002Tom Hack

12/03/1002

Introduction

Until now, power management in portable devices orsystems with battery backup have required a mix ofmajor components to fulfill the basic functions of batterycharging and generation of system supply voltages. A

typical solution requires at least one charger IC forcharging the battery, another IC to supply a regulatedsystem bus voltage from a constantly changing batteryvoltage, PowerPath control and a low dropout regula-tor (Figure 1).

Space is at a premium in these ever shrinking portableproducts, creating an imperative to shrink the powercircuitry as well. The LTC1980 solves the space problemby combining these functional blocks into a single IC. Theresult is a substantial reduction in the complexity ofportable power systems (Figure 2).

How the LTC1980 Reduces Size and CostThe LTC1980 manages both battery charging andgeneraton of the regulated system bus voltage via a uniquebidirectional pulse-width modulator design (Figure 3).

When the wall adapter is present, power passes directly tothe system load DC/DC converters and to a pulse width-modulated battery charger formed by M1, M2, T1 and theLTC1980. With the wall adapter present, power flows into

the battery. With the wall adapter removed, power flowsin the opposite direction, out of the battery, and is regu-lated through the DC/DC converter formed by the samepower components. In this way, a single bidirectional

supply replaces two traditional pulse width modulatedsupplies producing a substantial parts savings. No addi-tional power routing/management is needed, furtherreducing the parts count and power losses that would beincurred by the additional circuitry.

4.1V/1A Li-Ion Battery Charger and3.3V DC/DC Converter

Figure 4 shows a 4.1V/1A Li-Ion battery charger and 3.3VDC/DC converter. The LTC1980 includes a complete PWMregulator controller, PowerPath management functionsand charge termination (including pre-trimmed 4.1V,4.2V, 8.2V and 8.4V float voltages, under- and overvolt-

age protection, trickle-charge cell conditioning and chargetermination timing). Other battery chemistries may beexternally programmed.

This design is compatible with both regulated andunregulated wall adapters (minimum output voltage 4.1V).For higher voltage wall adapters, adjust R15 to increasethe wall-adapter detection threshold. D1 is optional andprovides protection against accidental wall-adapter con-nector shortsa problem in some products that usecharging cradles with exposed connections.

PowerPathCONTROL

LOW DROPOUTREGULATOR

TO SYSTEMLOAD DC/DCCONVERTERS

FROMWALLADAPTER

PWMREGULATOR

BATTERYCHARGER

CHARGETERMINATION

DN1002 F01

Figure 1. Traditional Portable Power System

TO SYSTEM LOADDC/DC CONVERTERS

FROM WALL ADAPTER

DN1002 F02

LTC1980-BASEDPOWER DESIGN

Figure 2. An LTC1980-Based Portable Power System

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

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LINEAR TECHNOLOGY CORPORATION 2003

dn1002 LT 1203 PRINTED IN THE USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 FAX: (408) 434-0507 www.linear.com

For applications help,call (408) 432-1900, Ext. 2593

Data Sheet Download

http://www.linear.com

LTC1980

ISENSE

Li-IonBATTERY

T1 WALLADAPTER

DN1002 F03a

SYSTEM LOADDC/DC

CONVERTERS

M1 M2

RS

LTC1980

ISENSE

Li-IonBATTERY

T1

DN1002 F03a

SYSTEM LOADDC/DC

CONVERTERS

M1 M2

RS

Figure 3. LTC1980 Bidirectional Power Conversion

(3b) DC/DC Converter Mode (Wall Adapter Removed)(3a) Battery Charger Mode

16

DN1002 F04

REG

MODE

BATT1

BATT2

VBATOVP

REGFB

CAOUT

C100.33F

PROG

C91FC8

0.1F

C70.27F R12

100k

R111M R13

806k

PROGT VC TIMER SS VBIAS1 VBIAS2

BGTDR PGND ISENSE RGTDR

LTC1980

GND

M1

1/2 FDC6401N

M2

1/2 FDC6401N

C6470F

R5154k

M3

R6100k

R7100k1%

R14100k

R8169k

OPTIONAL PASSTRANSISTOR

FOR LDO FDC636P

WALLADAPTER

SYSTEM LOADDC/DC

CONVERTERS

R910k

R10110k

C111nF

C1282pF

C168F

+ 4.1VLi-IonBATTERY

C468F

D1*5819

50mRSENSE

+ +

VREG LDO DRV LD OFB WA

VBAT VREG DCOUT

VOUT

ACIN5.1 5.1

1nF 1nF

*OPTIONAL DIODE FORSHORTED WALL ADAPTERTERMINAL PROTECTION.

R15221k1%18 15

9

10

14

1 2 4 17 24 13 19

12 20 21 11 7 6 5 8

23

3

22

BH511-10143.3V

200pF

VLDO3.1V

Figure 4. 4.1V/4.2V Selectable 1A Li-Ion Battery Charger and 3.3V DC/DC Converter

High Efficiency Makes for Cool Running Productsand Extends Operating Time Between Charges

Peak DC/DC converter efficiency, excluding the optional,low dropout regulator is over 88% (see Figure 5). Inaddition, the LTC1980 uses pulse-width modulated charg-ing. When compared to linear chargers, there is less powerdissipation keeping operating temperatures lower.

Conclusion

The LTC1980 helps reduce size, complexity and lowersthe cost of portable products by integrating a DC/DC con-

verter and battery charger circuitry into a single IC. It alsooffers high efficiency, increasing battery run time and low-ering power dissipation during battery charging.

LOAD CURRENT (mA)

10

EFFICIENCY(%)

90

85

80

75

70

65

60100 1000

DN1002 F05

VBAT= 3.6VTA= 25CFIGURE 4

Figure 5. Regulator Efficiency vs Load Current