This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM22677: Feedback resistor constraints vs. design guide suggestions for 24V output.

Part Number: LM22677

The datasheet for the LM22677-ADJ mentions how "A maximum value of 10 kΩ is recommended for the sum of RFBB and RFBT to maintain good output voltage accuracy" (page 15), while the design guide (www.ti.com/.../snva556.pdf) suggests a combination greater than 10kOhm for the 24V output (page 20). Which is better for accurate voltage output: keeping the sum of the resistors under 10kOhm, or using the 1kOhm resistor and 17.8kOhm resistor for the feedback resistors?

  • Hi Benjamin,

    Generally using lower feedback resistor values will increase voltage accuracy at the cost of leakage current. Since that design specification had high output voltage, the feedback resistors needed to increase in value. Going any lower than 1kohm on the bottom fb will create large leakage current on the FB pin.

    I would follow the design guide values. The maximum 10kohm is a recommendation and violating it will cause marginal accuracy loss in this situation. 

    Regards,

    Ethan

  • Thank you, Ethan!

    Benjamin