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TPS546D24S: Managing TPS546D24S with external DAC

Itay Yahav
Prodigy 10 points
Part Number: TPS546D24S

Tool/software:

Hello,

Is it possible to adjust TPS546D24S output voltage on-the-fly using external DAC and not via PMBUS?

Thanks,

Itay

  • 0
    TI__Expert 7546 points

    Hi Itay, 

    Yes, it can be done. You can treat VOSNS like a typical FB pin with respect to GOSNS and add a resistor divider network outside and the DAC.

    One thing to keep in mind is the impedance from VOSNS to GOSNS can vary about +/-30% between 85kΩ to 165kΩ (130kΩ typical), which will be in parallel with the bottom resistor, so you want to make sure to include that in your calculation of the output voltage.

    Thank you,
    Tomoya

  • 0 in reply to Tomoya Ide
    Prodigy 10 points

    Hi Tomoya,

    If I understand you correctly, the connection should be look like this:

    I'm not sure I can treat VOSNS like a typical FB pin because, FB pin is usually reference to a voltage, which is lower than the output voltage. So, the voltage at VOSNS should be equal to the desired output voltage.

    Moreover, do I need to take into account other configuration that affect the error amplifier, such as MSEL, VSEL, etc.?

  • 0 in reply to Itay Yahav
    TI__Expert 7546 points

    Hi Itay,

    Are you using PMBus at all? If not, would you be open to using our other non-PMBus, mid-VIN, high current devices? 

    Like you said, the device uses VOUT_SCALE_LOOP, which is an internal resistor divider that scale down to 1:1, 2:1, 4:1, and 8:1. If you use 1:1, then the internal reference will equal to the VOSNS with a 130k (typ) resistance from VOSNS to GOSNS with Vref = 0.4V (default). In that case, you can treat VOSNS like VFB. The issue with 1:1 is that it's only selectable through PMBus and not pin selectable, so if you're not using PMBus, this would not work. Using other scale loop might be possible, but the calculation can get more complicated, which I don't know if we want to go that route.

    Let me know your thoughts.

    Thank you,
    Tomoya