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DAC7311: Maximum current into Vout when Vdd = 0

Liam Powell
Prodigy 40 points
Part Number: DAC7311
Other Parts Discussed in Thread: DAC53204

Tool/software:

We would like to use a DAC for scaling the voltage of a SMPS via current-injection into the feedback pin, however in our application the SMPS output may be externally powered while the DAC Vdd rail is not. The datasheet for this DAC (and all the others I checked) says nothing about current flowing in to Vout when Vdd = 0, some mention current in to the input pins and others like the DAC7311 say absolutely nothing. Will this always damage the DAC or is a small current of a few milliamps safe?

  • +1
    TI__Mastermind 42203 points

    Hi Liam, 

    The output will be clamped to VDD through the ESD cell. Will there really be a few milliamps flowing in this case? Usually with SMPS there is a series resistor between the DAC and SMPS for the current injection and I typically see smaller current used there. 

    How long do you expect the SMPS to be powered on while DAC is powered off? I wouldn't recommend operating with this condition for long periods of time even with a limited current. 

    We do have the DAC53204 which is designed for this application and the output is hi-z even when VDD is off. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Prodigy 40 points

    The maximum current we'd see is going to be in the hundreds of microamps range after quickly checking.

    The user can theoretically connect a motor which may be externally driven for long periods of time to this SMPS output.

    The DAC53204 looks like a good option but it is more expensive than other DACs, we can go with that if there's not any DACs that are designed to handle continuous current injection.

  • +1 in reply to Liam Powell
    Prodigy 40 points

    It looks like most of the newer TI DACs have the same power-off high-impedance output spec, we'll look through all of those.