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Original question:

TPS65131: negative output voltage abnormal

TPS65131: How the values of R6 and R12 are determined

Liu Yang
Expert 5915 points
Part Number: TPS65131

Hi Team,

R6 and R12 in EVM board(TPS65131EVM-839) do not appear in typical application of datasheet, but no R6 and R12 output voltage is incorrect.
For EVM board, the output voltage is ±15V and R6 and R12 are 51.1k.
If the output wants to reach ±6.2V, what should be the values of R6 and R12 and other resistors.
Or how the values of R6 and R12 are determined.

Best Regards,
Tom Liu

  • 0
    TI__Expert 4940 points

    Hi Tom,

    I have notified our expert regarding this topic. Please expect a response by 5/5/20.

    Regards,

    Costin

  • 0
    TI__Mastermind 18550 points

    Hi Tom,

    R6/R13 have no impact on the output voltage value. In some nosier designs, we have noticed excessive noise coupling into feedback pins FBN/FBP through the feed forward capacitors C6/C9 and these resistors reduce this noise coupling by limiting the bandwidth of the feed-forward effect. So please use recommended value of 51.1K.

    Output voltage is calculated by the ratio of R3/R4 for VPOS and R5/R2 for VNEG. Please see datasheet equations 1 and 2 for calculating values of R3, R4 and R2,R5.  For +/-6.2V, following could be suitable values of the components:

    R3=534.4K

    R4=130K

    R5=619.4K

    R2=121.2K

    Capacitors C6 and C9 also need to be adjusted when you change the value of R3, and R5. Please see datasheet equations 11 and 12 to understand how to calculate value of these capacitors. With the above, value of R3=534.4K and R5=619.4K, C6 will be 12.7pF and C9 will be 12.1pF. You should use closest available standard value capacitor to these values.

    Kind Regards,

    Liaqat