decoupled cap in LTM8053

Hi,

as you are not able to find the a proper capacitance recommendation, I assume your desired input and output combination is not listed, please let us know which voltages are planned to used.

In the datasheet on page 16, it is mentioned that the listed capacitances values are the recommended minimum values. You can also install larger values. The use of ceramic capacitors is recommended, with a low ESR. Keep in mind, the recommended X5R and X7R capacitors are class 2 ones [1], which have reduced capacitance due to DC biasing (lower effective capacitance if operated close to the maximum rated voltage).

Kemet provides an online tool [2] where you can have a closer look on the impedance vs. frequency behaviour for different capacitor combinations.

Here, I would a use capacitance values which are close to your target voltages, you may use the next higher listed capacitance value. If possible, I would use capacitors with a higher voltage rating than the recommended ones (compared to the output voltage), if they are not too pricy. It seems, for the input they recommend 4.7u for every listed combination. Further, if you have no space limitations, include place holders where you might populate additional capacitors, if required.

Have you checked LTspice if this model is included? This would allow a preliminary test and a simulation based prediction, how the regulator behaves for different conditions e.g. load changes.

[1] https://www.eeworldonline.com/the-effect-of-dc-bias-on-mlcc-class-2-capacitors/
[2] https://ksim3.kemet.com/

BR

I think you're overthinking things.

Cin is typically not critical, and the table makes it pretty clear that they recommend a 4.7uF MLCC for all configurations. It's not surprising they also have a larger electrolytic cap on their demo board (can provide damping for the inductance of long wires connecting to Vin).

For Cout, the table gives a clear trend: lower Vout magnitude requires larger Cout. If your exact Vout is not on the table, just use the Cout for the nearest one, or interpolate nearby rows.