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LMR50410: Problems due to feedback resistance fluctuations

Conor
Mastermind 9310 points
Part Number: LMR50410

Hi,

As for the feedback reference voltage Vref, the data sheet states that Rfbt and Rfbb should be set so that the accuracy is ±1%. If the resistance value varies due to changes in resistance value accuracy and temperature characteristics, and the Vref error swings from ±1% to ±3~4%, what kind of problems may occur?

Thanks,

Conor

  • 0
    TI__Genius 13825 points

    Hi Conor,

    If the resistors are inaccurate, then the resistor divider in your feedback network may not be close enough to what your calculated values should be. If the resistor divider is off from calculations, you may notice that your output voltage is slightly off from what you calculated as well. Please follow all recommendations in the datasheet for your design.

    Best regards,

    Ridge

  • 0 in reply to Ridge Lahti
    Mastermind 9310 points

    Hi Ridge,

    The value of the feedback resistor is calculated using the following formula.

    Looking at the data sheet, the recommended value for RFBB is 22.1 kΩ. Could you please tell me why 22.1 kΩ is recommended? Also, if a value other than 22.1 kΩ is acceptable, could you please tell me the recommended resistance value range?

    Thanks,

    Conor

  • 0 in reply to Conor
    TI__Genius 13825 points

    Hello Conor,

    Usually RFBB is chosen, and then RFBT is calculated using that chosen RFBB value. The recommended range for RFBT is 10k-100k, and the 22.1k value was chosen to meet that requirement. There are other combinations that would be acceptable as long as RFBT is within the recommended range (see Section 8.3.2 of datasheet).

    Best regards,

    Ridge