DCP020515D output cap to reduce output voltage ripple

Amish Rughoonundon

Other Parts Discussed in Thread: DCP020515D

Hi,

I am using a DCP020515D to convert 5V to 15V. I would like to minimize the output voltage ripple to under 15 mV if possible. Can TI recommend any output capacitor (possibly 10uF with low ESR from my calculations) that would do the job assuming that the input voltage is perfectly flat. Thanks

Amish

over 14 years ago

0 Tom Guerin over 14 years ago

TI__Mastermind 38230 points

Amish:

I attached a PI filter using ceramic capacitors and ferrite beads( 1-5uH) for this request.The average ripple reduction is 10 -15db.

Tom

DCP022415D filter .pdf

0 Amish Rughoonundon over 14 years ago in reply to Tom Guerin

Prodigy 110 points

3326.10411772_3.pdf 7411.10411772_2.pdfHi Tom,

Thanks for the solution.

1) Is there a maximum ESR that the caps should have.

2) Does the size of the decoupling caps used at the loads matter?

I attached part of the design that uses the output.

Thanks

Amish3617.10411772_1.pdf

0 Tom Guerin over 14 years ago in reply to Amish Rughoonundon

TI__Mastermind 38230 points

Amish:

Thanks for the response .

1. The ESR on ceramic capacitors at this switching frequency is typically 3-6mΩ.

2.The ideal decoupling capacitors are ceramic types with X5R and X7R tolerance rating with 1.0uf to 4.7uF .Do not use Z5U or lower tolerance ceramic capacitors due their poor temperature ratings.

Tom

0 Amish Rughoonundon over 14 years ago in reply to Tom Guerin

Prodigy 110 points

Ok sounds good. I will try it out. Thanks,

Amish

0 Christoph Ruhland over 13 years ago in reply to Amish Rughoonundon

Prodigy 10 points

Hello together,

the post is already some months old but I have a question concerning the DCP02 series ripple filtering, too. I already wrote Tom an Email, but maybe it's better if I post it in the forum too:

There is one specific question which wasn't answered in different posts:
What's about the Y-Capacitor between input GND and output GND? Other DCDC
Manufactures propose this capacitor with high voltage durability and low
capacity (2.2nF - 100nF).

In our tests it was shown, that this capacitor has much more positive effects
than all PI-filtering at the input or output side of the DC/DC-Converter.

Does TI also recommend this GND/GND coupling? What's about the galvanic
isolation? Are there any side effects that come with this coupling?

Thank you very much for your help!

Regards
Christoph

0 Tom Guerin over 13 years ago in reply to Christoph Ruhland

TI__Mastermind 38230 points

The isolation coupling capacitor between Vin(-) and Vout(-) can be used for reducing EMI and reflected ripple. However, the voltage rating should be equal or greater than the converter 1 second isolation test or 2000V. The design of the DCx converters is fro ground fault isolation applications.

Tom

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DCP020515D output cap to reduce output voltage ripple