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UC1707: Max/Min Output voltage. What is it?

Stan Gibson
Prodigy 30 points
Part Number: UC1707

What is the maximum/minimum voltage on the output pins for the UC1707?  We are using the military part number 5962-8761901V2A.  We are considering what kinds of diodes we can use for protection on the outputs.

  • 0
    TI__Mastermind 22155 points

    Hey Stan,

    The maximum voltage the UC1707 will output is the Vc voltage. The minimum will be the GND voltage.

    Note there can sometimes be overshoot/undershoot due to parasitics.

    My suggestion for protection diodes would be having a schottkey diode to ground and a schottkey diode to Vc.

    This will make sure that the output is protected from voltage spikes caused by parasitics.

    Thanks,

    Daniel

  • 0 in reply to Daniel Hartung
    Prodigy 30 points

    If we have a  diode  with a 0.8V forward voltage will that damage the uc1707, because it may go higher than Vc

  • 0 in reply to Stan Gibson
    TI__Mastermind 22155 points

    Hey Stan,

    Is the diode a schottkey diode? 0.8 Volts seems quite high for diodes that are used as protection.

    Thanks,

    Daniel

  • 0 in reply to Daniel Hartung
    Prodigy 30 points

    No, the diode isn't a schottkey diode, but we can use one.  The 0.8V diode was one that we are using elsewhere on the board and can get stock of.  We are limited to the parts we can actually use because it is a space application, but the next one we found has a forward voltage of 0.4V.  Nonetheless this also will go above Vc.  Of course any diode will.  Just wondering if there was a limit below and above Vc and GND that we have to stay under to provide the needed protection. So if we connect Vc and Vin to 15V and Vc goes above 15V or below GND with the diodes, will that damage the chip?  Does the 40V max shown in the datasheet apply here? Same for the ground side.  It seems like that would be the case, so I am asking to be sure.

  • 0 in reply to Stan Gibson
    TI__Mastermind 22155 points

    Hey Stan,

    The reason I am asking about Schottkey diodes is because the diode needs a very fast reverse recovery to catch spikes if there are any on the output.

    If the output goes high enough above Vc to reverse bias the transistors there could be damage.

    The same is true with GND.

    Given that there is no datasheet specification on what this voltage is, I am unable to confirm whether 0..4 Vs is low enough, but I believe it will be

    I will say its not very likely to reverse bias the output with the small overshoot/undershoot spikes that will be seen, but I am unable to guarantee.

    Thanks,

    Daniel