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Designing for Very Fast Load Transients

PTH03010Y

PTH05010Y

PTH12010Y

SLTS223A–MARCH 2004–REVISED OCTOBER 2005

APPLICATION INFORMATION (continued)

Table 1. Input/Output Capacitors (continued)

Capacitor Characteristics

Quantity

Max Ripple

Capacitor Vendor,

Vendor

Working

Max ESR

Physical

Value

Current

Input

Output

Type/Series (Style)

Part Number

Voltage

at 100 kHz

Size

(µF)

at 85°CBus

Bus

(V)

(Ω)

(mm)

(Irms) (mA)

Panasonic, Poly-Aluminum:

S/SE (SMD)

6.3

180

0.005

4000

7,3 × 4,3 ×

2(2)

N/R(3)

EEFSE0J181R

4,2

Sanyo

SEPC, Os-con (Radial)

6.3

470

0.008

5700

10 × 13

1

≤1

6SEPC470M

SVP, (SMD)

6.3

470

0.015

4200

11 × 11,9

1

≤2

6SVP470M

TPE, Poscap (SMD)

6.3

470

0.018

3500

7,3 × 4,3

1

≤2

6TPE470MI

AVX, Tantalum TPS (SMD)

10

470

0.045

1723

7,3 L × 5,7 W

1

≤5

TPSE477M010R0045

× 4,1 H

10

470

0.060

1826

1

≤5

TPSV477M010R0060

Kemet, Poly-Tantalum

T520, (SMD)

10

330

0.040

1800

2

≤5

T520X337M010AS

4,3 W × 7,3 L

T530, (SMD)

10

330

0.010

5200

× 4H

2

≤1

T530X337M010ASE010

Vishay-Sprague

595D, Tantalum (SMD)

10

470

0.100

1440

7,2 L × 6W

1

≤5

595D477x0010r2t

94SP, Poly Aluminum (Radial)

10

470

0.015

4510

10 × 10

1

≤2

94SP477X0010FBP

94SVP, Poly-Aluminum (SMD)

6.3

470

0.017

3960

8 × 12

1

≤3

94SVP477X06R3E12

Kemet, Ceramic X5R (SMD)

16

10

0.002

–

3225 mm

1

≤5

C1210C106M4PAC

6.3

47

3225 mm

1

≤5

C1210C476K9PAC

Murata, Ceramic X5R (SMD)

6.3

100

0.002

–

3225 mm

1(4)

≤3

GRM32ER60J107M

6.3

47

3225 mm

1(4)

≤5

GRM32ER60J476M

16

22

1(4)

≤5

GRM32ER61C226K

16

10

1(4)

≤5

GRM32DR61C106K

TDK, Ceramic X5R (SMD)

6.3

100

0.002

–

3225 mm

1(4)

≤3

C3225X5R0J107MT

6.3

47

3225 mm

1(4)

≤5

C3225X5R0J476MT

16

22

1(4)

≤5

C3225X5R1C226MT

16

10

1(4)

≤5

C3225X5R1C106MT

(2) A total capacitance of 360 µF is acceptable based on the combined ripple current rating.

(3) N/R –Not recommended. The capacitor voltage rating does not meet the minimum derated operating limits.

(4) A ceramic capacitor is recoommended to compliment electrolytic types at the input to further reduce high-frequency ripple current.

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

1A/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 that specified in the data sheet, or the total amount of load

capacitance is above 8200 µF, the selection of output capacitors becomes more important.

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