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TPS65131: Condition when bandwidth-limiting resistor is needed

Ryotaro Fukui
Intellectual 2345 points
Part Number: TPS65131

Hello team,

I have a question about bandwidth-limiting resistor described in Datasheet 8.2.2.6.1.

It is explained that implementing this could avoid noise coupling into the control loop, and it is also implemented in the EVM. Though it was not listed in the 8.2 Figure 8. Typical Application schematic.

There were several cases in the E2E forum that circuit without this resister caused output instability. How should I think about conditions that require this resistance and the appropriate resistor values?

Also, when testing with a circuit without limiting resistor (same circuit as Figure 8), the output power was stable when the power consumption was low, so would it be related to power consumption?

Best Regards,
Ryotaro Fukui

  • 0
    TI__Mastermind 18550 points

    Hello Ryotaro,

    Conditions that require this resistor are dependent on the overall noise levels in the application and can be layout dependent. A practical approach can be to include 0 ohm series resistor and if both positive and negative converter outputs are stable under application conditions, then just use this zero ohm value. If one or both outputs exhibit instability, start out by putting a 10K resistor and increase its value until both rails are stable in the application circuit.  In general there is not a big draw back of adding the series resistor in the feedforward path so I suggest to implement it in your design. This resistor reduces noise coupling into FB pins and the compromise is slightly reduced loop response time but it is normally not an issue in most applications. Any values in the range 10K-100K should work.

    Kind Regards,

    Liaqat