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Issue with creating an Inverting Power Supply using the TPS54160

Rob Mitrunen
Expert 1685 points
Other Parts Discussed in Thread: TPS54160

My customer asks: We are having problems using the TPS54160. We are using this part as per the app note SLVA317A to generate a negative voltage. We pretty much used the exact same setup as the app note with minor changes to the voltage divider to generate -15V instead of the -12V in the app note. What we found is very strange. On our fully populated board, the -15V does not start up, it only goes to about -900mV. Then I populated just the TPS54160 device and its require components on a blank board and it was able to generate -15V.

This -15V rail on our board just feeds a -12V LDO. On the fully populated board, we removed this device and the -15V does not start up. I then thought that it might be the capacitors on the input of the -12V LDO so I added these to the blank board with just the TPS54160 and the -15v still works on the blank board. I also did a quick resistance measurement on -15V rail and it measures about 12K on the fully populated board so there is not a short.

I then replaced the old TPS54160 with a new part on the fully populated board and still it does not work. Also, I removed the 10K pull up on the EN pin for all of the experiments as this was a NC pin in the app note.

Please see attached schematic pages of the -15V circuit and the -12V LDO that is powered from the -15V.

I think the problem has to do with some interaction of the -15V regulator with the other circuits on our board. Also, I would like to know if TI has used this circuitry in a multi rail system. We currently product 5V, 3.3V, 1.2V, 12V, on our design but they are not connected in any way to the -15V.

 

 

 

  • 0
    TI__Guru 56925 points

    In this configuration, the IC's ground is connected to the -15V output.  With little to no load, there is no return path for the IC's ground current.  Try adding a 1kOhm dummy load resistor from -15V to GND.  This will provide a 15mA current path for the IC's ground.

  • 0 in reply to Peter James Miller
    Expert 1685 points

    Reply from the customer:

    I tried TI’s suggestion, but it did not help.

    I have seen some interesting behavior that I don’t quite understand that might be of use to TI. When I remove input capacitance between Vin and GND I was able to get -4.6V at the output.

    It would be useful to be able to simulate this setup, is there a spice model for this part that we can use or some other tool?

  • 0 in reply to Rob Mitrunen
    TI__Guru**** 191445 points

    It is likeley that there is some interaction between your external components and the system grounds.  Where is the powerpad connected?  Are there any sneak paths that are causing pre-bias on teh output?  Can you provide any waveforms showing good and bad start up?

  • 0 in reply to JohnTucker
    Expert 1685 points

    Customer replied: "Well we found our problem, it turns out that this a board issue. We received the rest of our board from our manufacturer yesterday, and this morning we noticed that the -15 regulator works just fine on at least two of them. This explains why it worked on the bare board as well. Thanks to everyone for their help."