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Original question:

TPS65130: Inverting converter is not regulating under load

TPS65130: Negative supply of the TPS65130 is not regulating

William Plumb
Prodigy 220 points
Part Number: TPS65130

Hi,

This was a follow on question from: [https://e2e.ti.com/support/power-management/f/196/t/727069?tisearch=e2e-quicksearch&keymatch=TPS65130]

From the query in the link

Query: Negative supply of the TPS65130 is not regulating under some conditions

Response : We have noticed that in nosier board environment, it is helpful to have a series resistor of around 51K between C14 and negative inverter output to reduce noise coupling into the FBN feedback pin.

We have had the same issue with our design where the inverting regulator is not regulating correctly resulting in a -19V output instead of the expected -10.5V. We added a 51kOhm resistor in series with C255 7.5pF - see attached diagram - and the output regulated to -9.5V. Is there a formula for calculating the value of the additional series resistor? Our design is slightly different from the one described in the link in that we are looking for a +10V/-10.5V output. If the output setting is changed does the value of the resistor also need to be changed?

Regards

Bill

partial_cy8c58lp_design_REV-A9_RELEASE_SCH.pdf

  • 0
    TI__Expert 6330 points
    Hi,

    I have notified our expert regarding this topic. Please expect a response by 12/6/18.

    Thanks,
    Aaron
  • 0
    TI__Mastermind 18550 points
    Hello Bill,

    I am glad that one of the other posts helped in debugging your issue. Out recommendation is to use a series resistor value of ~50K. There is not a formula but, basically, to reduce coupling noise into the control loop from the feed-forward capacitors, the feed-forward effect can be
    bandwidth-limited by adding a series resistor. Any value from 10 kΩ to 100 kΩ is suitable. The greater the resistance, the lower the noise coupled into the control loop system. The value of this series resistor is not particularly dependent on the output voltage.
    I hope my response is helpful.
    Kind Regards,
    Liaqat