TPS23755: reducing FRS capacitance

Alen Barisic

Part Number: TPS23755

Hi,

we use the TPS23755RJJR in our design and hear acoustic noise (whistling). If we reduce C657 from 2.2nF to 1nF there are no more noises.

Is this reduction acceptable? Are there any issues with that?

Thank you in advance!

Regards,

Alen

over 3 years ago

0 Darwin Fernandez over 3 years ago

TI__Mastermind 40120 points

Hi Alen,

A lower C657 capacitance for the same switching frequency will have a higher modulation frequency. This is okay since it is above the 11kHz recommended modulation frequency. The datasheet recommends higher than 11kHz. Thanks!

0 Alen Barisic over 3 years ago in reply to Darwin Fernandez

TI__Intellectual 1300 points

Hi Darwin,

Also we have EMC test issues. We have high pick at 250kHz (switching frequency) in all test (max hold & average).

Do you have any idea how can we get a better result? Knowing that we use your reference design.

0 Darwin Fernandez over 3 years ago in reply to Alen Barisic

TI__Mastermind 40120 points

Hi Alen,

Outside of dithering, to reduce 250hz range, you can try increasing the isolation caps (RTN to secondary ground). Also, you can replace the ferrite beads after the diode bridge with a common mode choke.

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TPS23755: reducing FRS capacitance