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LM4120: LM4120 total output capacitor

Yen Nee Lee

Prodigy 120 points

Part Number: LM4120
Other Parts Discussed in Thread: PMP21629

Hi,

Would like to check with you regarding the output cap requirement.

If we have one output X7R capacitor of 0.047uF directly at the output of LM4120, and another X7R capacitor of 0.047uF at the input of other destination IC, will the capacitance and ESR of this input capacitor be considered in the ESR and total capacitance requirement?

Thanks.

over 3 years ago

0 Trailokya Rai over 3 years ago

TI__Genius 11401 points

Hi Yen

Yes, the ESR of the input cap also will be considered in the calculation of the equivalent ESR.

Regards

Trailokya

0 Yen Nee Lee over 3 years ago in reply to Trailokya Rai

Prodigy 120 points

Hi Trailokya,

Currently my configuration is as mentioned above(2 x 0.047uF) with the below ESR performance. This part is used in the PMP21629 reference design.

With both parts placed in parallel, will the ESR reduced by half?

Any concern with the configuration?y

Thanks.

0 Trailokya Rai over 3 years ago in reply to Yen Nee Lee

TI__Genius 11401 points

Hi Yen

ESR looks higher than the data sheet recommendation. Please refer to section 8.1 (page 11) of the data sheet for output capacitor and ESR.

Regards

Trailokya

0 Yen Nee Lee over 3 years ago in reply to Trailokya Rai

Prodigy 120 points

Hi.

What is the frquency of interest that we need to meet the esr of less than 0.5? By paralleling the two capacitors will the total esr reduce?

Thanks.

0 Trailokya Rai over 3 years ago in reply to Yen Nee Lee

TI__Genius 11401 points

Yen

Please use 2 capacitors with less than 1 ohm ESR over the frequency.

It's not recommended to use capacitor with such high ESR. It can make it unstable with any surrounding noise.

Regards

Trailokya