TPS56428: Output Capacitor Selection

Rob McCullough

Part Number: TPS56428

The datasheet for this device specifies output capacitance values from 20-68uF. Are these values nominal values? Or are they referring to the effective capacitance values? Since these are high dielectric constant ceramic capacitors, they have a large de-rating based on DC bias. We are specifying two 47uF capacitors, which, nominally, is outside of the 20-68uF range. But the effective capacitance with de-rating is within the range. Is this the correct way to specify these capacitors?

over 2 years ago

0 Zixu Wang over 2 years ago

TI__Expert 8100 points

Hi Rob,

These values are nominal values.

BRs

Zixu

0 Rob McCullough over 2 years ago in reply to Zixu Wang

Prodigy 10 points

This is confusing to me. If I specify two 22uF capacitors that have a DC bias de-rating of 80% at 3.3V (effective C = 8.8uF), or two 22uF capacitors that have a 40% de-rating at 3.3V (effective C = 26.4uF), how can both of these values be acceptable?

Even though both of their nominal capacitance values are within the range the datasheet gives, one capacitor set gives 3 times the effective capacitance.

0 Zixu Wang over 2 years ago in reply to Rob McCullough

TI__Expert 8100 points

Hi Rob,

I will check and give you feedback later!

BRs

Zixu

+1 Zixu Wang over 2 years ago in reply to Rob McCullough

TI__Expert 8100 points

Hi Rob,

Sorry for late response. Since it is old part, I have made double check that listed output capacitor values are effective values.

BRs

Zixu

0 Rob McCullough over 2 years ago in reply to Zixu Wang

Prodigy 10 points

So the values listed in the datasheet are the effective capacitance values?

0 Zixu Wang over 2 years ago in reply to Rob McCullough

TI__Expert 8100 points

Hi Rob,

You can regard it as effective value of output capacitors in TPS56428 datasheet.

BRs

Zixu

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TPS56428: Output Capacitor Selection