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LMZ31710: controlling output voltage dynamically by the VADJ pin

guy lemire
Intellectual 970 points
Part Number: LMZ31710
Other Parts Discussed in Thread: UCD9090A, , TPSM84A21, LM10010, TPSM846C23

Hello,

I am using the LMZ31710 currently in a design and I am fixing the output voltage using the rset resistor. I also use the UCD9090A, to sequence this supply and to margin voltages on some linear supplies. I wanted to know if I could add a margining circuit from the UCD9090A to the VADJ pin so that I could move the output voltage up/down depending on the requirements. I am looking at a range of perhaps 1.1 to 1.9V output.

If so is there an example design that I could look at.

Or is there another supply that you could recommend that could be controlled directly via a PMBus?

Regards,

Guy

  • 0
    TI__Guru 50120 points

    Hi Guy,

    I think a simple yet effective way to dynamically control the output voltage of any power module is using an externally injected digitally controlled current source. There is already an app note available on the web that goes over the general idea of how this works (SLVA861) using the TPSM84A21 but the logic should still be applicable to any power module. 

    Here the top and bottom feedback resistor sets the range of the controllable output voltage. Equation 1 shows that the larger the top resistor, the wider your output voltage range is at the cost of precision. 

    Have a look at the reference and let me know if you have any questions on this.

    Regards,

    Jimmy 

  • 0
    TI__Genius 17905 points

    Hi Guy,

    Yes it should be possible to adjust the output dynamically with an external circuit like UCD9090A. Take a look at this app note which uses a LM10010/1 to adjust the LMZ317xx output dynamically as well.

    We have TPSM846C23 35A device with PMBus and margining, but that may be more output current capability than your applicaiton needs.

    Regards,
    Kris