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Part Number: TPS7A19
My customer is considering feed forward cap for noise reduction.
Could you please help my customer calculate feed forward capacitance for TPS7A19 and TPS7A25 respectively? How much CFF is recommended for the condition below?
Vin = 16.4V and Vout = 11.5V. Iout = 0.15A.
I know zero is needed to be placed before unity gain frequency by LDO Basics.
But it doesn't provide specific formula and guideline, so I'd like to learn more that.
We don't normally provide calculations for adding a feed-forward capacitor (CFF). We do show plots for our lower noise LDOs. Here is a summary from the LDO basics series:
Here is where a CFF helps PSRR:
And here is how CFF impacts noise:
The below chart shows the impact on noise (TPS7A91 example):
For this adding more than 100nF does not have a significant benefit.
So I would recommend trying a value between 10nF and 100nF for either device.
I hope this helps.
John Cummings 蔣康明Texas Instruments 德洲儀器Johncummings@ti.com
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