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TPS62112 reverse leakage

Ytai Ben-Tsvi
Prodigy 100 points
Other Parts Discussed in Thread: TPS62112

Hi,

The datasheet for TPS62112  says "the reverse leakage current is specified under electrical characteristics", but I couldn't find it there. Does anyone know what it is? Also, is my understanding correct that this is the maximum current that will go from output to input in case the input is disconnected and the output is driven?

Also, would like feedback on the following idea: I need to drive a line with 5V either from the TPS or from an external source. I need the TPS to take precedence when it has input power. I'm putting a PNP between the external source and the output, and the gate will be pulled down, and then driven by something that says "TPS is working" to disable the external source. So far so good, but the standard circuit for that feeds the base from TPS output, and a diode is required. But I cannot tolerate its voltage drop.

So my idea was to drive the base from the TPS input. Only problem is that if the input is disconnected and the output is 5V, current will leak. Will a simple resistor (small enough) from Vi to GND do the trick, i.e. ensure that the input voltage is small when it is disconnected?

Thanks!

  • 0
    TI__Guru*** 144820 points

    That paragraph refers to the situation where the part is disabled yet there is a voltage present on the output for some reason.  So, where might this voltage leak to in the IC?  If there is a voltage on Vout, then there is a voltage on SW.  A voltage on the SW pin would leak through the low side MOSEFT, which is the N-channel MOSFET.  There might also be voltages on LBO and PG, depending on their connection and usage in the schematic.  All of these leakages are specified.

    You could also post in the power interface forum for a suggestion to your OR-ing requirement.  I would highly recommend testing any solution you find to this issue before going to production.

    Instead of using the TPS6211x family, I would suggest you look at the brand new TPS6214x or TPS6216x device families.

  • 0 in reply to Chris Glaser
    Prodigy 100 points

    Thanks for the quick response, Chris!

    Chris Glaser said:

    That paragraph refers to the situation where the part is disabled yet there is a voltage present on the output for some reason.  So, where might this voltage leak to in the IC?  If there is a voltage on Vout, then there is a voltage on SW.  A voltage on the SW pin would leak through the low side MOSEFT, which is the N-channel MOSFET.  There might also be voltages on LBO and PG, depending on their connection and usage in the schematic.  All of these leakages are specified.

    I'm not currently using LBO and PG, but won't the high-side mosfet have a body diode that will cause leakage from SW to Vin?

    And on the same note - if there's indeed such leakage - do I need to pull EN down to GND to prevent the switcher from running whenever there's voltage on SW and Vin is floating?

    Chris Glaser said:

    You could also post in the power interface forum for a suggestion to your OR-ing requirement.

    Good idea, thanks.

    Chris Glaser said:

    I would highly recommend testing any solution you find to this issue before going to production.

    This is a good practice in general :)

    Chris Glaser said:

    Instead of using the TPS6211x family, I would suggest you look at the brand new TPS6214x or TPS6216x device families.

    I'll have a look.

  • 0 in reply to Ytai Ben-Tsvi
    TI__Guru*** 144820 points

    Yes, there is a diode pointing from SW to Vin.  That paragraph assumes that the device is disabled yet Vin remains.  So, in this case, if Vin is > than Vout (which it should be for a step-down converter), then there will be leakage from Vin to SW.

    If Vin is not present, the SW node voltage will appear on Vin minus a diode drop.  Pulling EN to GND won't disable that body diode.  Vout will appear on Vin minus a diode drop.  You'll need to add a diode to the input side to block the voltage from going upstream.

  • 0 in reply to Chris Glaser
    Prodigy 100 points

    Thanks, this is very clear, and unfortunately bad news for me...

    I'm trying to avoid losing a diode drop in my design. I'm trying to figure out a mosfet-based workaround for this issue. I'll raise this as a post to the forum you pointed me to.