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Designing for Load Transients

PTN04050C

SLTS251 – SEPTEMBER 2005

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

required 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 of

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. Obey the minimum ESR and maximum capacitance limits specified in the

Electrical Characteristics table.

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

BUS

(V)

CURRENT

(mm)

(ESR) (

Ω)

Panasonic FC( Radial)

25

180

0.117

555

8 X 11

1

1

EEUFC1E181

Panasonic FC (SMD)

25

100

0.30

450

8 X 10,2

1

1

EEVFC1E101P

United Chemi-Con PXA (SMD)

16

150

0.026

3430

10 X 7,7

1

1

V)

PS

25

100

0.020

4320

10 X 12,5

1

1

25PS100MJ12

LXZ

25

100

0.250

290

6,3 X 11,5

1

1

LXZ25VB101M6X11LL

MVY(SMD)

35

100

0.300

450

8 X 10

1

1

MVY35VC101MH10TP

Nichicon UWG (SMD)

50

100

0.300

500

10 X 10

1

1

UWG1H101MNR1GS

F559 (Tantalum)

10

100

0.055

2000

7,7 X 4,3

1

HD

25

100

0.130

405

6,3 X 11

1

1

UHD1E101MER

Sanyo Os-Con SVP (SMD)

20

100

0.024

2500

8 X 12

1

1

20SVP100M

16SP100M

SP

16

100

0.032

2890

10 X 5

1

7,3L X 4,3W

TPSV107M020R0085

20

100

0.085

1543

1

X 4,1H

AVX Tantalum TPS (SMD)

TPSE107M020R0200

20

100

0.200

> 817

1

GRM32ER60J107M

Murata X5R Ceramic

6.3

100

0.002

>1000

3225

1

C3225X5R0J107MT

TDK X5R Ceramic

6.3

100

0.002

>1000

3225

1

GRM32ER61C476M

Murata X5R Ceramic

16

47

0.002

>1000

3225

2

C1210C476K9PAC

Kemet X5R Ceramic

6.3

47

0.002

>1000

3225

2

C3225X5R0J476MT

TDK X5R Ceramic

6.3

47

0.002

>1000

3225

2

GRM422X5R476M6.3

Murata X5R Ceramic

6.3

47

0.002

>1000

3225

2

C3225X5R1E2265KT/MT

TDK X5R Ceramic

16

22

0.002

>1000

3225

5

(1)

Capacitor Supplier Verification

1. Verify availability of capacitors identified in this table. Capacitor suppliers may recommend alternative part numbers because of

limited availability or obsolete products. In some instances, the capacitor product life cycle may be in decline and have short-term

consideration for obsolescence.

RoHS, Lead-free and Material Details

2. Consult the capacitor suppliers regarding material composition, RoHS status, lead-free status, and manufacturing process

requirements. Component designators or part number deviations can occur when material composition or soldering requirements are

updated.

(2)

voltage, select a capacitor with a higher voltage rating.

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