LM5119: Maximum values for current sense filter

Andrew Dunlop

Part Number: LM5119

Hi.

I have some noise present on the CS and CSG pins of an LM5119 due to adjacent circuitry (another LM5119) switching at inconvenient moments. They are synchronised, so it happens rather predictably.

Adding a 1nF / 100R / 100R differential filter improved the situation dramatically, but there is some residual noise affecting the current measurement. I know this because the input current draw changes (reduces) if the source of noise is removed.

My questions are:

1. What are the maximum permitted values for the differential current sense filter components? I presume that the consequence of lowering the current sense filter bandwidth too far will be reduced accuracy / sensitivity to overcurrent conditions. My switching frequency is 250kHz.

2. Are there any other strategies for reducing the sensitivity to noise of the CS and CSG pins?

Thank you in advance!

Kind regards,
Andrew

over 4 years ago

0 Qian Chen over 4 years ago

TI__Mastermind 24075 points

Hi Andrew,

1. You are right. Large R-C-R filter may reduce over current accuracy.

2. The noise coupling issue should be solved by layout. Make CS and CSG signals away from noise source such as switching node, gate drive signal and etc.

Also, the R-C-R filter should be close to controller, not sensing resistor, so the noise coupled to the trace can be filtered out.

Thanks

Qian

0 Andrew Dunlop over 4 years ago in reply to Qian Chen

Prodigy 200 points

Hi Qian,

Your points are well noted. Thank you.

Andrew

Power management

Power management forum

LM5119: Maximum values for current sense filter