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LM2675: ADJ - switching Vout via switched resistor?

Reha Elci
Prodigy 30 points
Part Number: LM2675

Hi there,

For the FB pin, is it possible to switch on additional resistor via mosfet (e.g. 2n7002) to GND? I am looking to digitally switch Vout depending on need (by pulling down an additional resistor to GND). 

I realize FB stability is very important however I can't see any info on output response if FB were to change. 

Thanks

  • 0
    TI__Mastermind 34275 points

    Hi Reha,

    First, you need to test loop response at all target Vout and make sure loop is stable, then the Vout can be changed by adjusting FB low-side resistor via MOSFET, you may need to limit the MOSFET turn-on speed if the the Vout under/over shoot is too big.

    B R

    Andy

  • 0 in reply to Andy Chen
    Prodigy 30 points

    Thanks Andy,

    I will test the stability - it is probably a good idea to limit the turn on speed anyway. If it is unstable I could probably also afford to shutdown the switcher (via the pin) before turning on the mosfet. Looks like I need to experiment some.

    Thanks for your help.