A5974D datasheet(22/46 Pages) STMICROELECTRONICS

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Application information

A5974D

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DocID018774 Rev 2

Tantalum capacitors:

Very good, small tantalum capacitors with very low ESR are becoming more available.

However, they can occasionally burn if subjected to very high current during charge.

Therefore, it is better to avoid this type of capacitor for the input filter of the device.

They can, however, be subjected to high surge current when connected to the power

supply.

High dv/dt voltage spikes on the input side can be critical for DC/DC converters. A good

power layout and input voltage filtering help to minimize this issue. In addition to the above

considerations, a 1 µF/50 V ceramic capacitor as close as possible to the VCC and GND

pins is always suggested to adequately filter VCC spikes.



Output capacitor

The output capacitor is very important to meet the output voltage ripple requirement.

Using a small inductor value is useful to reduce the size of the choke but it increases the

current ripple. So, to reduce the output voltage ripple, a low ESR capacitor is required.

Nevertheless, the ESR of the output capacitor introduces a zero in the open loop gain,

which helps to increase the phase margin of the system. If the zero goes to a very high

frequency, its effect is negligible. For this reason, ceramic capacitors and very low ESR

capacitors in general should be avoided.

Tantalum and electrolytic capacitors are usually a good choice for this purpose. A list of

some tantalum capacitor manufacturers is provided in Table 7.

Table 6. List of ceramic capacitors for the A5974D

Manufacturer

Series

Capacitor value (µF)

Rated voltage (V)

TAIYO YUDEN

UMK325BJ106MM-T

MURATA

GRM42-2 X7R 475K 50

4.7

Table 7. Output capacitor selection

Manufacturer

Series

Cap value (µF)

Rated voltage (V)

ESR (m

)

Sanyo POSCAP(1)

1. POSCAP capacitors have some characteristics which are very similar to tantalum.

TAE

47 to 680

2.5 to 10

25 to 35

68 to 330

4 to 6.3

25 to 40

AVX

TPS

100 to 470

4 to 35

50 to 200

KEMET

T494/5

100 to 470

4 to 20

30 to 200

Sprague

595D

220 to 390

4 to 20

160 to 650

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