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LP3985IM5X-2.5 How to eliminate a initial output spike when apply input voltage?

Leo Chang1
Prodigy 30 points

The enable pin 3 has a strong pull down to GND, 2.2K.  During power up, 3.3V is applied to VIN pin 1.  We are seeing a spike on VO pin5, that caused logic error in the subsequent circuit.  (VO goes to a IC programming input.)  We need the output muted/tristated during power up until enable EN pin 3 goes high by software control. 

1.  How do we fix this? 

2.  If not, is there an alternative part?

Thank you for the help!  //leo

  • 0
    TI__Prodigy 80 points
    hi Leo, Thanks for your question.
    In your application , What's the value for Cin , Cout and Cbypass? Could you inform your application condition? Thanks.
    I checked Start-up polt on datasheet, there is no spike found. Test condition is "Cin = Cout = 1 μF Ceramic, Cbypass = 0.01 μF, VIN = VOUT + 0.2 V, EN pin is tied to Vin".
    Best regards Bing