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LM4368 - Problems with added EMI filter

Question asked by TDJ on Jul 31, 2018
Latest reply on Aug 14, 2018 by Manpreet

Hi. We are using an LM4368-2 designed to the following specs:

UV protection = 10.8V
OV protection = 36V (actual value is 35.6V)
OC protection = 8.9A
1200ms cooldown

 

Firstly, this is how our circuit behaves upon power ON, without the PI filter:

DC_Vin = 22.0V: fault lasts 5 sec then OK
DC_Vin = 30.0V: fault lasts 1 sec then OK
DC_Vin = 34.5V: fault lasts 4 sec then OK
DC_Vin = 34.7V: fault lasts "constantly" (why can't we reach the intended OVP value of 35.6V?)

 

After the filter is added big problems arise. Ultimately, we are no longer able to use the high end of our supply voltages because when power is applied at these levels the circuit starts making a clicking and doesn't leave FAULT mode. Are there any known issues with using the LM4368 with large input inductance and/or capacitance? Is our output/load capacitance too high? Any idea what may be causing these problems? Circuit is attached.

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