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LM5069: Filtering Out Sub 10us Current Spikes

Part Number: LM5069
Other Parts Discussed in Thread: TPS1653

Hi Ti Team, 

We are using the LM5069 as an eFuse to provide soft-start, short circuit and over current protection to an auxiliary power rail. We recently lowered the LM5069 current limit to 1.2A,min 1.375A,typ and 1.5A,max and during testing we found that when our system experiences a heavy load though our main power path the auxiliary power path, which is monitored by the LM5069, sees a quick blip of current for about less than 10us at a peak of 1.7A to 2.5A. During this time the circuit breaker protection is tripped and our auxiliary power line is down for about 10s before the LM5069 starts back up. 

We need to keep the current limit set at this range due to current limitations up stream from the LM5069. So what we'd like to do is create a small RC filter on the SENSE input for the LM5069 so that these short sub 10us pulses are filtered out without having a major impact on short circuit performance. We'd like to place a capacitor where the DNM R141 is located and a resistor where R125 is located.

Are there any limits to the values of the R in the RC filter? Some of our tests showed that the LM5069 would turn off the FET if R was 50ohms. Why is that? We don't want to introduce another issue with this solution.

We are testing short circuit reaction times and our Taus are being kept low as low as possible.

Circuit without RC filter, which was seeing the circuit breaker issue:

  • Hi Nick,

    There should not be any effect with RC filter other than slowing down the short circuit response. We limit the RC time constant to <1us so that it won't stress the FET for real short fault.

    TPS1653 is right fit for your application with transient 2x pulse support 

    Best regards,

    Rakesh