STMicroelectronics Evaluation board for A5970AD EVALA5970AD EVALA5970AD Hoja De Datos
Los códigos de productos
EVALA5970AD
Application information
A5970AD
22/42
DocID14661 Rev 5
Capacitors that can be considered are:
Electrolytic capacitors:
These are widely used due to their low price and their availability in a wide range of
RMS current ratings.
The only drawback is that, considering ripple current rating requirements, they are
physically larger than other capacitors.
Ceramic capacitors:
If available for the required value and voltage rating, these capacitors usually have
a higher RMS current rating for a given physical dimension (due to very low ESR).
The drawback is the considerably high cost.
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.
These are widely used due to their low price and their availability in a wide range of
RMS current ratings.
The only drawback is that, considering ripple current rating requirements, they are
physically larger than other capacitors.
Ceramic capacitors:
If available for the required value and voltage rating, these capacitors usually have
a higher RMS current rating for a given physical dimension (due to very low ESR).
The drawback is the considerably high cost.
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.
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.
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
some tantalum capacitor manufacturers is provided in
Table 6. List of ceramic capacitors for the A5970AD
Manufacturer
Series
Capacitor value (µF)
Rated voltage (V)
TAIYO YUDEN
UMK325BJ106MM-T
10
50
MURATA
GRM42-2 X7R 475K 50
4.7
50