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LM3485: The influence of inductance size on output voltage

Part Number: LM3485
Other Parts Discussed in Thread: LM3489EVAL


1.The input voltage is 24V, and the output voltage is 3.6V;

2.Please help confirm the impact of the size of the inductance on the output voltage. We have used two brands of inductors in use, one with a measured inductance value of 43uH and the other with a measured inductance value of 47uH. The result is that the voltage at 43uH is close to 3.6V, while the voltage at 47uH is close to 3.72V.

  • Hello,

    Are you saying that for the same exact schematic components other than the output power inductor, you are getting two different output voltage regulation points (43uH results in 3.6V) and (47uH results in 3.72V)? Also was this on the same board? 



  • hi jimmy:

     on the same board, two different output voltage regulation points (43uH results in 3.6V) and (47uH results in 3.72V)  


  • Hello,

    There is no particular reason why the output regulation would change between different inductors assuming the feedback divider network is the same. The output voltage regulation point is set by the top and bottom feedback resistors and follows Equation 1 which is not dependent on inductor value:

    I would suggest testing on a LM3489EVAL board and configure components to your values to evaluate this device. 

    Can you try doing this and get back to me on the results?

    This is to rule out any issues with PCB layout.

    Also it would be good to have a waveform measurement of VOUT and SW for both configurations with different inductor values just to see what the switching behavior looks like.