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TSP5420 Start-up problem low Vin

justin judkins
Prodigy 10 points
Other Parts Discussed in Thread: TPS54227, TPS62120, TPS54062

I have a TSP5420 in an application where the Vin has some input resistance. My circuit is set up for 5V output at 30mA and the input is 9V. However, because of the source impedance the inrush current pulls the input down to UVLO and the output is shutoff. The chip tries to start every 200 msec but can never achieve steady state. If I increase Vin to 14 volts then it will start. It will then continue to operate if I turn the voltage back down to 9 volts.

Is there a way to extend the start-up time, or keep the gate drive on longer to overcome this start-up transient? I am using .01uF BOOT capacitor.

 

  • 0
    TI__Guru**** 191445 points

    The BOOT cap does not really affect that.  What you need a a device with adjustable slow start.  For only 30 mA output yo may be able to get a way with a non adjustable slow start part such as TPS54062 or TPS62120.  Other wise you could try TPS54227 2A w/ adjustable slow start.