TPS51200-Q1: LPF R4 C9 reference value

Neal Zhu

Part Number: TPS51200-Q1
Other Parts Discussed in Thread: TPS51200

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1016629/tps51200-q1-lpf-r4-c9-reference-value#

The recommended value of R4 / C9 is 10 ohm / 0.1uF，Is there a formula for this，R4/C9 value is depending on the parasitic and ESR/ESL of the capacitors

but EVM recommended value of R4 / C9 is 10 ohm / 10pF，How to calculate the value of resistance and capacitance？

https://www.ti.com.cn/cn/lit/ug/sluu323/sluu323.pdf?ts=1629254766817&ref_url=https%253A%252F%252Fwww.ti.com.cn%252Ftool%252Fcn%252FTPS51200EVM%253FkeyMatch%253D%2526tisearch%253Dsearch-everything%2526usecase%253Dpartmatches

over 3 years ago

0 Zhao Gao over 3 years ago

TI__Prodigy 480 points

We received your request and let me make the calculation and then reply to you.

Best,

Zhao

0 Zhao Gao over 3 years ago in reply to Zhao Gao

TI__Prodigy 480 points

I think you are talking about 10uF rather than 10pF.

For the C9 in first datasheet is for TPS51200 but the C9 for second data sheet is for a different device. It is not the same cap.

Best,

Zhao

0 Neal Zhu over 3 years ago in reply to Zhao Gao

Expert 2470 points

Is there a calculation formula, that is, how to calculate the capacitance and resistance values,

To explain to the customer why the capacitance is changed from 10PF to 10uF, the tps51200 will not have a very high temperature when it is started.

Thanks！

0 Zhao Gao over 3 years ago in reply to Neal Zhu

TI__Prodigy 480 points

Hi Neal,

where did you get the 10pF number from? In your second datasheet. It mentions C9=10uF, but it is a different cap to TPS51200

Best,

Zhao

0 Neal Zhu over 3 years ago in reply to Zhao Gao

Expert 2470 points

The EVM is C15 ,sorry,R4/C9 is customer SCH thanks!

0 Zhao Gao over 3 years ago in reply to Neal Zhu

TI__Prodigy 480 points

Sorry, now it is clear.

The C9 is a practical number to filter some high frequency noise. customer need watch out the Vo signal and adjust C9 until Vo is clean. Frequency = 1/(2pi*RC) and you want to have the C9 greater than your noise frequency.

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TPS51200-Q1: LPF R4 C9 reference value