www.ti.com

Designing for Load Transients

PTH04070W

SLTS227B – SEPTEMBER 2004 – REVISED OCTOBER 2007

The transient response of the dc/dc converter has been characterized using a load transient with a di/dt of

1 A/

μs. The typical voltage deviation for this load transient is given in the data sheet specification table using the

optional value of output capacitance. As the di/dt of a transient is increased, the response of a converter's

regulation circuit ultimately depends on its output capacitor decoupling network. This is an inherent limitation with

any dc/dc converter once the speed of the transient exceeds its bandwidth capability. If the target application

specifies a higher di/dt or lower voltage deviation, the requirement can only be met with additional output

capacitor decoupling. In these cases, special attention must be paid to the type, value, and ESR of the

capacitors selected.

If the transient performance requirements exceed those specified in the data sheet, the selection of output

capacitors becomes more important. Review the minimum ESR in the characteristic data sheet for details on the

capacitance maximum.

Table 3. Recommended Input/Output Capacitors

CAPACITOR CHARACTERISTICS

QUANTITY

85

°C

CAPACITOR VENDOR/

EQUIVALENT

VENDOR

WORKING

MAXIMUM

PHYSICAL

COMPONENT

VALUE

SERIES

INPUT

OUTPUT

NUMBER

VOLTAGE

RIPPLE

SIZE

SERIES

(

μF)

RESISTANCE

BUS

(V)

CURRENT

(mm)

(ESR) (

Ω)

Panasonic WA (SMT)

10

120

0.035

2800

8

×6.9

1

FC (SMT)

25

47

0.400

230

8

×6.2

1

Panasonic SL SP-cap(SMT)

6.3

47

0.018

2500

7.3

×4.3

1

≤ 3

EEFCD0J470R

6.3

56

0.009

3000

7.3

×4.3

1

≤ 2

EEFSL0J560R

United Chemi-con PXA (SMT)

10

47

0.031

2250

6.3

×5.7

1

1

PXA10VC470MF60TP

FS

10

100

0.040

2100

6.3

×9.8

1

≤ 5

10FS100M

LXZ

16

100

0.250

290

6.3

×11.5

1

1

LXZ16VB101M6X11LL

MVZ (SMT)

16

100

0.440

230

6.3

×5.7

1

1

MVZ16VC101MF60TP

Nichicon UWG (SMT)

16

100

0.400

230

8

×6.2

1

1

UWG1C101MCR1GS

F559(Tantalum)

10

100

0.055

2000

7.7

×4.3

1

≤ 5

F551A107MN

PM

10

100

0.550

210

6

×11

1

1

UPM1A101MEH

Sanyo Os-con\ POS-Cap SVP

10

68

0.025

2400

7.3

×4.3

1

≤ 5

10TPE68M

(SMT)

6.3

47

0.074

1110

5

×6

1

≤ 5

6SVP47M

SP

10

56

0.045

1710

6.3

×5.0

1

≤ 5

10SP56M

AVX Tantalum TPS (SMD)

10

47

0.10

1100

7.3L

×4.3W

1

≤ 5

TPSD476M010R0100

10

47

0.060

> 412

×4.1H

1

≤ 5

TPSB476M010R0500

Kemet T520 (SMD)

10

68

0.060

>1200

7.3L

×5.7W

1

≤ 5

T520V686M010ASE060

AO-CAP

6.3

47

0.028

>1100

×4.0H

1

≤ 3

A700V476M006AT

Vishay/Sprague 594D/595D

10

68

0.100

>1000

7.3L

×6.0W

1

≤ 5

594D686X0010C2T

(SMD)

10

68

0.240

680

×4.1H

1

≤ 5

595D686X0010C2T

94SL

16

47

0.070

1550

8

×5

1

≤ 5

94SL476X0016EBP

TDK Ceramic X5R

6.3

22

0.002

>1400

1210 case

≤ 3

C3225X5R0J226KT/MT

Murata Ceramic X5R

6.3

22

0.002

>1000

3225 mm

≤ 3

GRM32ER61J223M

Kemet

6.3

22

0.002

>1000

≤ 3

C1210C226K9PAC

TDK Ceramic X5R

6.3

47

0.002

>1400

1210 case

≥ 1

≤ 3

C3225X5R0J476KT/MT

Murata Ceramic X5R

6.3

47

0.002

>1000

3225 mm

≥ 1

≤ 3

GRM32ER60J476M/6.3

Kemet

6.3

47

0.002

>1000

≥ 1

≤ 3

C1210C476K9PAC

(1)

A ceramic capacitor is required on both the input and the output. An electrolytic capacitor can be added to the output for improved

transient response.

(2)

An optional through-hole capacitor available.

(3)

A total capacitance of 44

μF is an acceptable replacement for a single 47-μF capacitor.

10

Submit Documentation Feedback

Copyright © 2004–2007, Texas Instruments Incorporated

Product Folder Link(s): PTH04070W