LM5148: output capacitor

Hi,

Ceramic caps are generally used in buck topologies because of:

1. High operating Temperature range

2. Low Rdson 

3. Relatively low cost (for lower capacitance values)

Other most common type used is Electrolytic - however, these have high ESR - this makes the power loss in these caps high and worsens the transient response. 

There is almost always a trade-off when selecting between capacitors. Quoting from this app note: https://www.ti.com/lit/an/slyt639/slyt639.pdf (which I recommend you read):

"Ideally, the output capacitor would be very large for energy storage and have very low impedance at the loop crossover and switching frequencies. Polymer and tantalum capacitors come in large values with low ESR, but they are expensive and the ESR is still not as low as a ceramic capacitor. Electrolytic capacitors are very good for obtaining large capacitance values at a low cost, however, they have a larger ESR and ESL. This makes them unsuitable for output load-step performance. Ceramic capacitors have very low ESR and ESL that makes them great for transient performance, but they have limitations on capacitor size. Ceramic capacitor values of 22 µF and less are relatively inexpensive. The effective capacitance of ceramic capacitors decreases with bias voltage, which makes it more difficult to provide enough energy storage for large load steps"

The device has no limitation on what type of capacitor you use. The only thing you need to make sure is that the loop is stable across all operating parameters. In my personal view, and also according to the app note - the best way forward is a combination of two - Electrolytic and Ceramic. 

Hope this helps,

Thanks,

Best Regards,

Taru

Hi,

Thank you for the clear and quick answer.

Best Regards,