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Original question:

TPS65131-Q1: Having a problem with Inverting Buck-Boost

TPS65131-Q1: Having a problem with Inverting Buck-Boost

Ramazan Yaman
Prodigy 50 points
Part Number: TPS65131-Q1
Other Parts Discussed in Thread: TPS65131

Dear Expert

Note that this is related to TPS65131-Q1 having a problem with Inverting Buck-Boost question

Your previous recommendation caused us to have -10V as output voltage instead of -12.5V, so problem was solved thanks to you. After that I tried to get -5V output voltage for an input voltage value of 5V. Up to 4V as the input voltage, an output voltage of -5V is generated without any noise. However, the circuit is out of regulation for input voltage values, which are greater than 4.1V. Looking at the scope, we see that for input voltages, which are greater than 4.1V, the output voltage goes up to -6.5V approxmately in 1.2ms and then the circuit cannot regulate itself. The output voltage swings from -2V to 0V, there is no -5V. Do you have any recommendation for this problem?

Best regards,

Ramazan Yaman

  • 0
    Prodigy 50 points
    Note that the load resistance is equal to 30Ohm
  • 0
    TI__Mastermind 18550 points
    Hello Ramazan,
    I would not expect any problem for generating -5V with Vin greater than 4.1V so not sure what is causing issues with your design. Can you please attach schematics of the TPS65131 section of your circuit so that I can review to see if I can spot an issue?
    Kind Regards,
    Liaqat
  • 0 in reply to Liaqat Khan
    Prodigy 50 points

    Hello Liaqat,

    The schematic is attached

    Best regards,

    Ramazan Yaman

  • 0 in reply to Ramazan Yaman
    TI__Mastermind 18550 points
    Ramazan,

    It is interesting that you are not using the boost converter at all. I have not seen anyone only using the inverting converter on this device but that should be fine.

    After reviewing the schematics, I suggest to replace L3 with a 100 ohm resistor as shown in the typical application circuit in the datasheet. This bead likely has much lower resistance at DC than the 100 ohm. Also, I am not not sure where the capacitor C2 is located on the board in relation to L3 but I would suggest to have a capacitors of at least 4.7uF close to L3 after you have replaced L3 with 100 ohm resistor.

    I don't see any thing else wrong with your schematics so I hope that this change improves the behavior you are observing.

    Kind Regards,

    Liaqat