Cookbook DC DC

8/19/2019 Cookbook DC DC

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DC/DC conversion Cookbook

A simple step by step guide to select the most appropriate

voltage regulator for your application

Piercarlo Scimonelli


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Presentation outline

• What you need to know, to discuss intelligently

• Checklist and Selection Procedure

• Examples / ST products

2


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3

Voltage Regulators

A Voltage Regulator keeps a constant Output Voltage with varying:

• Output current

load regulation

• Input voltage line regulation

Voltage

Regulator

Input VoltageOutput Voltage

(Iout)

The three most important parameters: Vin, Vout, Iout

(Vout)(Vin)

Output Current


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4

Ideal Voltage Regulator V-I Characteristic

Vout

Iout


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5

Voltage Regulator simplified block diagram

Voltage regulators operate by comparing the output voltage to an

internal fixed reference. The difference is amplified and used to control

the output voltage. This is what we call a closed-loop feedback.


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6

Classification of power switching topologies

Source: APPLICATION BRIEF 0014 (N.Siciliano)


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Step down Converter (Buck)

ISW1

ISW2

IL

Vsw

Io

Vo

TON

T

T D

V

V ON

IN

O

T

TON

SW2

SW1 IL

Io


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Closing the loop – Voltage Mode

VC

sawtooth

D·Ts

Ts

Closed Loop Feedback (Voltage Mode)

L597x

L598x

L798x


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RSEN

Vin

L

Co

R Vo

PWM

Comparator

Slope

vc

Vref

R1

R2

VFB

iL signal

Ki

Error

Op-Amp

Compensation

Network

Slope comp

Inductor

current signal

Error OpAmp output (Vc)

Closing the loop – Current Mode

Closed Loop Feedback (Current Mode)

D·Ts

Ts

ST1Sx

L692x


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Power dissipation in Voltage Regulators

1) Power dissipated when the switches are closed (conduction losses):

PON = IOUT2 x (RDSONHS x D + RDSONLS x (1-D) + RL)

2) Power dissipated during the commutations (switching losses):

PSW = VIN x IOUT x FSW x (TON + TOFF)/2

3) Power dissipated when the device is not switching:

PQ = VIN x IQ

Power dissipated in a linear regulator:

PD = (VIN-VOUT) x IOUT + VIN x IQ


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Example: low Iq regulators in powering STM32

Current consumption:• Depends on operating mode

• Decreases at lower VDD

• Inreases with temperature

• Increases with clock speed

Supply current in standby is the same order of magnitude as the quiescent current

of voltage regulators

STM32L Vcc: 1.8V to 3.6V, Icc: 1uA to 100mA


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Input Voltage from 1.5V to 5.5V Ultra Low Quiescent Current:

1.0 μA (typ) at no load 1 nA (typ) in OFF mode

Fixed VOUT: 0.8V to 3.3V Excellent load transient response Stable with low ESR, SMD ceramic caps

STLQ015150mA, Ultra Low Quiescent Current LDO regulator

SOT666-6L (1.2x1.6mm)


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Switching Frequency ImpactPerformance

• Efficiency (needs low frequency)

• Thermal (needs low frequency) • Output Voltage Ripple (needs h igh frequency)

• Dynamic Performance (need h igh frequency)

• Board space availability (needs h igh frequency)

Typical cases:

~100kHz

To maximize

efficiency (Energy

harvesting) SPV1040

250-500KHz

High voltage buckregulators(Industrial/Automotive)L7985, L7986,PM668x

600KHz-1MHzCost/performancetrade-off

(Consumer/Computer)ST1S40, L6738

1MHz-3MHzPortableapplications / sizeconstraints(Trade off betweenboard space and

efficiency)ST1S31/32,STBB1, STLA02

3MHz up to6MHzExtreme boardspaceconstraints(PortableFitness, Smartphones/tablets)

STBB2,ST1S15


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High efficiency at light load: L6925/6/8Step-down switching regulators

• VIN : 2V 5.5V (2.7V 5.5V for L6925)

• VOUT: adjustable 0.6V VIN (100% DC)•

1% output voltage accuracy

• IOUT up to 800mA• 25uA quiescent current• Selectable Low noise or low consumption mode (PWM/PFM)• Freq.: 600KHz, synchronizable up to 1.4 MHz (L6925/6)• Freq.: 1.4MHz synchronizable up to 2 MHz (L6928)

• Current Mode Control• Thermal shut down (150C)

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Differentiating functions:

L6925: LBI & LBO, UVLO @ 2.7VL6926/L6928: PGOOD & RUN

L6925


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L6928 low noise or low power (burst) mode

16

Low noise

Forced PWM

Burst mode

High efficiency

Vin 4.2VVout 1.5V

Iout 30mA

Cin/Cout 10uF

Rc 20Kohm

Cc 330pF


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Switching regulator selection based on output current

Single Output Switching Controller: external mosfets, up to30A load, very high efficiency

Switching Converter: internal mosfet(s), up to 5A load, compact

Multiphase controllerLoad higher than 30AHigh efficiency, low ripple, fasttransient response, small i/o filters

Multi-Output Controller or ConverterCompactness

HS1

LS1

HS1

LS1

HS1LS1

HS2

LS2

HS1

LS1

HS2

LS2


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The drop-out voltage is the minimum voltage across the regulator to maintain regulation

LDO: Low Drop-Out (voltage regulator)

Vin

Vout

Vin - Vout

Vin

Vout

Vin - Vout

Vin

VoutVin - Vout

Standard Linear

Regulators

(L78xx, LM317)

Vdrop >2V

Semi Low-Drop

(LD1117/LD108x)

Vdrop 0.8V-1.5V

Very Low-Drop

(LFxx/LD29xxx) Vdrop 0.2V-0.7V

Ultra

LDO (LD39xxx)

Vdrop


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Load Transient Response

VIN=12V, VOUT=3.3V, SRILOAD=2.5A/us

IL

0.5A/div

VOUT AC coupled

100mV/div

COUT=47uF

L=6.8uH

FSW=500kHz

Timescale

100us/div


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STLQ015 Load Transient

Load Transient Response

VIN=5.5V CIN=1µF, COUT=10µF, IOUT= from 1µA to 10mA

Vout

Iout

Tradeoff between:

BW of Error Amplifiervs.

Power consumption

Static Load Regulation

{{Load Transient response


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Soft-Start

2

11

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6.0

R

RSRSR

F

SR

VREF VOUT

SW

VREF L598x• Staircase ramp on internal VREF• 64 steps, 9mV each step

• 32 clock cycles each step


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24

Synchronous rectification vs. non-synchronous

ST1S10

L7981

Is a synchr. converter

always more efficient

than a non-synchr?


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Application requirements in a DC/DC conversion - summary

• Input Voltage (VIN)

• Output Voltage (VOUT)

• Output DC current (IOUT)• Power Conversion Efficiency: a measure of power losses smaller package

and longer battery life

• Switching frequency: ON/OFF time of power switch Impacts size of external

components and efficiency

• Quiescent Current (Iq): required to power internal circuitry Impact on light

load efficiency• Package Thermal Resistance Rth: ability to dissipate heat impact on board

space and robust thermal design

• Switching control (PWM – PFM): noise vs. efficiency at light load

• Feedback loop (Voltage Mode vs. Current Mode)

• …

The best device

is that which fits

the application


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• From Vin and Vout, select the topology (step-up, step down, buck-boost)

• Based on the output current and efficiency, choose between controller (ext.

FETs), converter (int. FETs) or Linear

• Select the device starting from the input voltage spec and max DC current

(if integrated FETs) to meet the application requirements of input voltage

range and load

• Consider any other design constraint: operating temperature range,

switching frequency, quiescent current, light load efficiency,synchronization, board space, transient response, power good, soft start,

output ripple etc… etc…

• Always ask what is “key” to the application

DC/DC Selection Procedure Summary


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PMICs

ASSP

ASICs

Switching Converters (int. FET)

& LED drivers

Battery & Power Management

Switching Controllers (ext. FETs)

Single and Multi output

Single and Multi phase

Power over Ethernet (PoE)

DC-DC Conversion Portfolio27

Linear Voltage Regulators

Low Drop Out (LDOs)

Shunt Voltage Ref.


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Switching Converter segmentation28

Automotive Grade, high Vin

A597x, A798x

Consumer Value Line

12V Vin, 3-4A, synchr.

ST1S40, ST1S41

Synchronous, high at light load

PMxx, ST1Sxx, L692x

Battery powered applications

L692x, PM6644, ST1S1x

Non synchronous, high Vin

ST1S14, L798x, L597x, L598x

High performance, 3-5A synchr.

PM8903, ST1S31/2, L5988/89

Continuous output current from 350mA to 4A

Wide range of max input voltage: 5V TO 60V

SOT23, Q/DFN3x3 and 4x4mm, HSO8, and TSSOP


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Step Down Converters – First buying choice

0

10

20

30

40

50

60

0 1 2 3 4 5 6

MAXIMUM OUTPUT CURRENT

L5970

ST1S06

ST1S03

ST1S14

L7981

L6925/6/8

ST1S10

ST1S09ST1S12

ST2S06

L5986L5985/45

L5973/4A

L5983

L5972/3A

L5981L5980

Synchronuos

NON-Synchronous

ST2S08

L4976 L4971 L4978 L4973

L6902

ST1S30ST1S15

Synchr. high at light load

PM8903ST1S03A

PM6644

ST1S41L5987/47

ST1S40

L5988/89

L7986L7985

L7980

L5974/5A L5975

ST1S32ST1S31

PGood

M A X I M U

M O

P E R A T I N G I

N P U T V O L T A G E


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2-3A output current in QFN3x3-10L and HSOP8 packages

P-channel power MOS: 100% DC operation and no bootstrap capacitor

High switching frequency (250KHz, adjustable up to 1MHz) withSynchronization capability (180° out of phase)

Wide input voltage range (4.5V up to 38V)

200ns minimum Ton

Internal Soft-start

Enable pin

Embedded protection features Suitable for MLCC output filter

Typ RDSon=150mΩ

L7985-L7986

QFN 3x3 10L - Rth j-amb 60

C/W

HSO8 - Rth j-amb 40° C/W

L7986/A

L7985/A 2A / up to 1MHz

3A / up to 1MHzQFN10 3x3 HSOP8


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Switching Frequency: 800kHz

Continuous output Current Capability: 3/4A 4/5A peak current limit

Output Voltage: Adjustable from 0.8V

Operating Input voltage 4V to 18V

Ceramic Capacitors and small Inductor

Soft-Start integrated circuit

Integrated 69mOhm Low side R DSon Integrated 95mOhm High side R DSon

Efficiency: up to 95%

Enable pin or Power Good

SO8, HSOP8 and MLP4x4 packages

Pin-to-pin with ST1S10

ST1S40/41

ST1S41 4A / 850kHz

ST1S40 3A / 800kHzDFN – 8L4x4mm

SO-8

HSOP-8

Package OutputCurrent

Commercial Code

SO8 3A ST1S40IDR

SO8-BW 3A ST1S40IPHR

DFN4x4 – 8L 3A ST1S40IPUR

DFN4x4 – 8L 4A ST1S41PUR

HSOP8 4A ST1S41PHR


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PM6644350mA step down and 3.3V voltage reference

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4.5V to 25V input voltage range (35V AMR)

Vout: fixed 3.465V or adjustable 0.9V to 8V 350mA valley current limit

Constant On-Time Control

Progr. switching frequency in PWM mode

Pulse skipping mode at light load

Latched OVP and UVP

High accuracy (±0.6%) 3.3V reference


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LDO Positioning (≤500mA)

0

5

10

15

20

25

30

0 100 200 300 400 500 600 M A X I M U M O

P E R A T I N G I

N P U T V O L T A G E

P. Scimonelli - APM – Jun 2011

ST715

L4931

STLQ50

LD2980

LD39050

LDFMxx

LFxx

KFxx

Ultra-low drop VDROP


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LDO Positioning (≥500mA)

0

5

10

15

20

25

30

35

0 500 1000 1500 2000 2500 3000 3500

MINIMUM GUARANTEED OUTPUT CURRENT

P. Scimonelli - APM – Jun 2011

LD39050

AG

LD39080

LD29080

LD1117

LD39100

ST1L02

ST1L04

LD1117A

L4941

L4940

LD1086

ST1L05 LD49150

LD29150

LD39150

LD49300

LD39300

LD29300

LD1085

LDFMxx

LFxx

KFxxLDFMxx

Ultra-low drop VDROP


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LDOs in portable applications

• LD39015J: 150mA - CSP4 bumps 1x1mm2

• LD39115J: 150mA - CSP4 bumps 0.8x0.8mm2

• LD39030SJ : 300mA, Soft-Start - CSP4 bumps 0.8x0.8mm2

• LD59015: 150mA, Very High PSRR, SC70

• LDCL015: 150mA – Capless, SOT23

• LDLN015: 150mA – Very Low Noise, DFN2x2

• LD39130: 300mA - CSP4 bumps 0.69x0.69mm2 and DFN 1.2x1.3

DC/DC i f 5V Vi l

http://images.google.it/imgres?imgurl=http://erinni.files.wordpress.com/2008/06/apple_ipod_nano.jpg&imgrefurl=http://erinni.wordpress.com/2008/06/30/ipod/&usg=__RD5Nd8I_7OJnH512YXjFQWRyc38=&h=389&w=295&sz=11&hl=it&start=4&um=1&tbnid=zLQaciAPDhb53M:&tbnh=123&tbnw=93&prev=/images?q=ipod+nano&hl=it&um=1http://images.google.it/imgres?imgurl=http://axelll.files.wordpress.com/2009/07/apple-netbook-tablet.jpg&imgrefurl=http://axelll.wordpress.com/2009/07/19/macsipad-the-apple-netbook/&usg=__xHjW2at35br09GFp1LQTraQP22Y=&h=306&w=540&sz=44&hl=it&start=7&um=1&tbnid=SBbiZk653Dg58M:&tbnh=75&tbnw=132&prev=/images?q=apple+netbook&hl=it&um=1


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DC/DC conversion for 5V Vin or lowerVoltage Regulation & Battery Chargers

STBB1 Buck boostSTLQ015 1.7uA Iq, 150mA Iout, LDOSTLQ50 3 μA Iq, 50 mA Iout, LDO

LD39015/LD39115 Low noise, 150 mA Iout, on/offL6924D Lithium battery chargerSTW4102 – Lithium Battery chargerL6920D 1 A step-up, low Iq, down to 0.6 VinL6928 Sync step-down, 95 % 2-5.5 VinST1S15 - 500mA, 6MHz, high efficiency buckPM6644 - 350mA, high efficiency buck + 3.3V VrefSPV1040 boost with MPPT for solar battery chargersLMV4041- 1.2V Vref with 0.1% accuracy in SC70

Display drivers STLA02 (6 LED backlight driver)STLED25 (2x5 LED backlight driver)STP2/4CMP (2/4 ch charge pump)STODxx (AMOLED)


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DC/DC conversion for 12V Vin

Part Numb er V INPUT /V OUT range F SW features Package

L6726A, L6727Up to 19V VINPUT,

0.8V min VOUT 270/300khZ EN, SS, OCP, OVP, UVP SO8

L6728Up to 13,2V (15V ABS) VINPUT,

0.8V min VOUT300/600KHz EN, SS, OVP, OCP, PGOOD DFN10

L6725, L6730

L6731, L6732

4.5V to 14V VINPUT,

0.6V min VOUT Up to 1MHz

OVP(Latch - No Latch), UVP, OCP (CC or HICCUP),

PGOOD (with adj. delay) , SS (Sink - No Sink), IHN, Extor Internal REF, Adj UVLO, SYNC., Sink- No sink cap.

SO16N

HTSSOP16

QFN24 4x4

HTSSOP20

L6738Up to 19V VINPUT,

0.8V min VOUT Adj.

EN, SS, OVP, OCP, PGOOD, differential CS &

“GREEN low power mode” QFN16 3x3

• Consumer

• Computer

• Anything powered off your friendly wall wart

CONTROLLERS (Ext.FETs)

CONVERTERS (Int.FETs)


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DC/DC conversion for 24V to 55V Vin

PNVOUT #

(SW +LDO)

VOUTSW

1

VOUTSW

2

VOUTS

W 3VOUTLDO(S) ILDO VIN range package

PM6670/A 1+1 Adj. - - VINLDO /2 2A Up to 28V /36V QFN 4x4

PM6675/A 1+1 Adj. - - Adj. 2A Up to 28V/36V QFN 4x4

PM6680/A 2+1 Adj. Adj. - 5V 200mA Up to 28V/36V QFN 5x5

PM6681/86 2+1 Adj. Adj. - Adj. 100mA Up to 28V QFN 5x5

PM6685 2+2 3.3V 5V - (1)3.3V + (2)5V 100mA up to 28V QFN 5x5

• Industrial Applications

• Printers

• Automotive/Marine battery

Powered applications

CONTROLLERS (Ext.FETs)

CONVERTERS (Int.FETs)


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Tools and resources

D i S it


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eDesign Suite www.st.com/edesignstudio

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Complete designs in a few steps starting from input voltage, output voltage and current

Interactive schematics and BOM: change the parameters of external components

Evaluate the performance of your design: stability, thermal, efficiency,…

Connect to Cadence® Orcad Pspice


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A complete design in a few steps…..

Login to

www.st.com/edesignstudio

(after online registration)

Input your specifications

The design is ready

Create a new project and

choose an application type


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Helps select the optimal IC for your needs

You can filter the IC selecting specific features


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Evaluate the performance of your design

Simulates key voltage and current waveforms, displays bode plots, power losses and efficiency

Loss distribution

Waveforms simulator Bode plots

Efficiency


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Your design gets portable and exportable

Save your project to ST server/eDesign Studio My Projects folder

It can accessed from ANY computer through your eDesign Studio account

Export the current design project for Pspice Simulat ion in OrCAD


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Print a summary of your project


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Parametric Search on www.st.com 46

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Cookbook DC DC

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