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TPS65253 Start Up

John Garrett
Expert 4210 points
Other Parts Discussed in Thread: TPS65253

I have a customer who is seeing odd start up behavior whereby the EN pin appears to be internally pulled down to ground a couple times before the TPS65253 starts up.  The EN pin doesn't connect to anything other than a small 1000 - 4700pF cap to ground.  

What I did notice is that the soft-start capacitor in their design is quite large (0.22uF) - yielding a very high soft start time (approx. 35ms).  The data sheet references a watchdog timer on the Power Good that fires in 10ms, recommending a soft start time of 5ms.  Could the too large soft start capacitor be causing this type of behavior on the EN pin and thus affect start up?

Please let me know.

Thanks, John Garrett AFA