slyt302.pdf

Texas Instruments Incorporated

Power Management

New current-mode PWM controllers

support boost, flyback, SEPIC and

LED-driver applications

By Jürgen Schneider, Systems Engineer Power Solutions

Features

Introduction

With their wide input voltage range, the TPS40210 and

TPS40211 PWM controllers are targeted for isolated and

non-isolated power converters used in industrial, automo-

tive, and battery-powered applications. The full freedom in

selecting the power stage and its compensation—as well

as the advanced features, such as programmable soft start,

adjustable/synchronizable oscillator frequency and internal

slope compensation—supports the use of the devices in

many applications. The basic converter architecture can

provide different power levels by simply changing the

power stage. While the TPS40210 is designed for general-

purpose applications, the TPS40211 is tailored for driving

high-brightness LEDs.

Boost converter application

The devices and their basic configuration are described

in detail in Reference 1.

SEPIC converter application

The SEPIC-converter shown in Figure 1 allows the input

voltage to be smaller, larger, or equal to the targeted out-

put voltage. The topology requires two single inductors

or one coupled inductor, L1, and a capacitor C9, which is

responsible for the energy transfer. The filter formed by

L2 and C11 is optional. It reduces the output ripple volt-

age to 50 mV p-p in the example shown. When operating

the converter at 1 MHz, the size of the power stage

(inductors/capacitors) can be minimized. However,

Input voltage: 4.5 to 52 V

Current-mode architecture

Switching frequency: 35-kHz to 1-MHz

(programmable and synchronizable)

Programmable soft start (closed loop)

Reference voltage: 700 mV for TPS40210

and 260 mV for TPS40211

Internal slope compensation

Threshold for overcurrent detection: 150 mV

Internal 8-V regulator and N-channel MOSFET

driver

Quiescent current when disabled: 10 µA

MSOP10 PowerPAD™ and 3-mm x 3-mm

SON package

due to the increased switching loss at this high frequency,

a greater than 1-A continuous output current requires Q1

to be mounted on a heat sink. Operation without a heat

sink is possible at a reduced switching frequency and/or

reduced maximum input voltage.

With a 2-A current output and a 1-MHz switching

frequency, converter efficiency was measured as follows:

90% with a 12-V source, 88% with a 24-V source, and

85% with a 36-V source.

Figure 1. SEPIC 1-MHz converter with 8- to 36-V input and 12-V/3-A output

VIN+

8 V to 36 V

L1 4.7 µ

1 µ

C11

1 µ

150 k

100 n

3.3 µ

Optional lter

to reduce ripple

F Switching = 1 MHz

DIS/EN

COMP

VDD

VBP

GDRV

ISNS

GND

Q1 Si7850DP

on heatsink

for I OUT > 1 A

VOUT+

12 V/3 A

100 p

2 x

3.3 µ

100 k

MBRB2060CT

4.7 n

R4 1 k

PwPd

6.19 k

0.01

1 µ

100 p

220 n

200 k

TPS40210

C10

2 x 22 µ

C12

330 µ

Analog Applications Journal

3Q 2008

www.ti.com/aaj

High-Performance Analog Products

Power Management

Texas Instruments Incorporated

Flyback converter application

Figure 2 shows the TPS40210 controller configured in

a flyback-converter topology for a dual-output isolated

supply. Key components include the transformer (T1),

the snubbers (R5, C7, D1, R8, C9, R10, R11, C12 and

C13), the optocoupler (U2), the secondary-side reference

and error amplifier (U3), the bias resistor (R15) belonging

to U3, the loop compensation (C19, C20 and R16), the

output-voltage divider (R17 and R18), and the secondary-

side soft-start and overshoot control (D5, R14 and C18).

The circuit shown directly controls the positive output

rail (V OUT +) only. Negative-rail regulation is based on

the cross regulation between the two secondary windings

of T1. When the negative output does not have a load,

R12 and D4 provide a basic load.

High-brightness LED-driver application

DC/DC regulators are usually designed to provide a con-

stant-voltage output; however, LED applications require a

constant-current output. In Figure 3, R1 is used to sense

the LED current. The losses in R1 are minimized with the

TPS40211 because of its low 250-mV reference voltage.

D1 protects against output overvoltage in the event of

an LED-string open circuit. The brightness can be

programmed by altering R1, current injection into the

FB pin, or by PWM dimming. See Reference 1 for more

information.

Figure 3. 700-mA high-brightness LED driver

...

V OUT : 20

38 V/I OUT : 700 mA const.

B2100

...

0.37 @

700 mA

30 k

4.7 µ

VIN+

8 V to 18 V

L 1 10 µ

0.1 µ

2.2 µ

R25 402 k

F Switching

400 kHz

DIS/EN

COMP

VDD

VBP

GDRV

I SNS

GND

R6 3.3

C3 100 p

R7 1 k

0.018

14.3 k

100 p

100 n

1 n

1 µ

220 p

TPS40211

References

For more information related to this article, you can

download an Acrobat Reader file at www-s.ti.com/sc/

techlit/ litnumber and replace “litnumber” with the TI

Lit. # for the materials listed below.

Document Title TI Lit. #

1. “TPS40210/211” data sheet . . . . . . . . . . . . . . . . .slus772

Related device

TPS40200—4.5- to 52-V wide input range step-down

converter

www.ti.com/sc/device/TPS40200

Related Web sites

power.ti.com

www.ti.com/sc/device/TPS40210

Figure 2. Isolated flyback converter with a 10- to 14-V input and ±12-V/0.5-A output

MBRS260

R5*

20 k

VOUT+

+ 12 V/0.5 A

VIN+

10 V to 14 V

C7*

0.1 µ

C14

22 µ

4x22 µ

0.1 µ

C12*

470 p

C16

10 µ

R10*

R11*

301 k

D1*

MMSD4148

R12**

100

C15

22 µ

C13*

470 p

C17

10 µ

470 p

F Switching = 250 kHz

Si4850EY

D4**

MMSZ13ET1

VDD

VBP

GDRV

ISNS

GND

DIS/EN

COMP

MBRS260

47 p

1 00 n

R8*

100

VOUT–

– 12 V/0.5 A

220 p

R7 1 k

0.012

PwPd

R15

1 k

R17

20 k

R14***

1 k

R13

2 k

150 p

T PS40210

30 k

1 µ

C18

***

4.7 µ

C19

120 p

D5***

BAV99

C20

2.7 p

TCMT1307

10 k

1 k

C10

4.7 n

R16 7.5 k

R18

5.23 k

C11

4 .7 n

TL431ACDBZ

* Snubber for reduction of voltage stress and improved EMI

** Clamps negative output in case of heavily unmatched loads

*** Soft start and overshoot control

Analog Applications Journal

High-Performance Analog Products

www.ti.com/aaj

3Q 2008

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SLYT302

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