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LM3481-Q1: Will a Zener Diode on FA pin affect frequency accuracy?

Part Number: LM3481-Q1
Other Parts Discussed in Thread: LM3481

Hi Team,

Our customer is considering the following setting to control LM3481-Q1 on/off, but the voltage range of KL30 is 6~18V, higher than the maximum 6V FA pin can accept from the datasheet. So they're considering to connect a 5.1V zener diode to FA pin to clamp the voltage, but they're not sure if the zener diode will affect the setting frequency accuracy/variation. Would you please give some comments on that? Thanks.

Best Regards,


  • HI Yazhu Liu,

    Thanks for reaching out with your question and for considering the LM3481 in your design.

    If the customer is worried about the leakage current of the zener diode shifting the frequency then the diode should be moved. It would be possible to attached the cathode of the zener between the pull down MOSFET and the 10kOhm resistor. This will keep the FA/SYNC/SD pin from exceeding the absolute voltage rating and not cause a shift on the switching frequency.

    Please let me know if you have any questions.