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TPS5410 DROP OUT PROBLEM

WhiteHorse
Genius 4430 points
Other Parts Discussed in Thread: TPS5410

e2e

Our Customer is having a Vout dropout problem on TPS5410.  See attached “Bad.jpg” file. Ch1 (yellow) is the Vout, while ch2 (red) is pin8 (PH). This happen when they turn on a couple of boards using TPS5410 as the power source. The board current is only 6.6mA each, so they don’t think this is a load problem plus it does not happen by increasing the load. Another strange thing is when R3 (1.78k-ohm) was removed it fixed the problem on one board.  It didn't work on another board.  Schematic is attached. 

Example of properly working response (good.jpg)

 

Example of dropout.  (bad.jpg)

What could be causing the regulator to operate such as this?

Thanks for your help.

Regards,

4478.4682.TPS5410 Schematic.pdf

  • 0
    TI__Guru**** 191445 points

    First can you explain the operation?  It looks like you are turning the supply on and off.  The time base is very long.  You will need to trigger on the falling edge of Vout.  Check the PH waveform as well as VIN right at the IC.  Also, Can you provide a clear schematic?  the included bitmap is too blurry to read.