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TPS63020 unstable with no load

Kevin Lowderman
Intellectual 870 points
Other Parts Discussed in Thread: TPS63020

I have a TPS63020 design that is unstable with no load.

- Is there a minimum load requirement?

- PS/SYNC is pulled low.

-Vin is 5V

- Feedback is 3M (Vout to FB) and 499K (FB to GND). The problem is intermittent but much better when these are changed to a 1M and 200K.

Does the TPS63020 support a no load condition?

Are there any guidelines or requirements when using the TPS63020 in a no load condition?

 

 

 

  • 0
    TI__Guru**** 150770 points

    Yes, the TPS63020 is stable with no load.  Can you post a waveform of what is unstable?  In power save mode, there will be more output voltage ripple than usual.

    Since smaller feedback resistors eliminate the problem, they can be confirmed as causing the problem.  The datasheet recommends that the lower resistor be around 200k.  The resistors can be made as small as desired with the only consequence of lower efficiency at light loads.  The upper limit for the values is based on the FB pin input current and noise.  With larger resistors, there is less current in the voltage divider.  Thus, the FB input current is a larger percentage of the divider current and can cause large errors in Vout.  Also, with larger resistors, the very sensitive FB pin is made even more high impedance.  Thus, noise will easily couple into it and could cause problems.

    If you are not testing on the EVM, I recommend getting an EVM and testing on it, which is a known good layout.