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SN74LVC126A: Output Behaviour When Not Supplied

Jakob Z
Prodigy 55 points
Part Number: SN74LVC126A

Tool/software:

Hi,

what is the expected behaviour of the SN74LVC126A outputs in case the supply voltage (VCC) and output enable (OE) are not supplied / low / equal to GND? Thanks in advance.

Best regards,

Jakob

  • +1
    Guru 311870 points

    The output will be disabled, but the body diode of the output's P-channel MOSFET creates a current path from the output to the VCC pin.

  • 0 in reply to Clemens Ladisch
    Prodigy 55 points

    So if VCC is low (GND) and a 200k resistor is connected from the output to 1V8 the body diode should not be conducting right?

    I am asking because this is the exact setup I am facing: VCC and OE low / GND and a 200k resistor connected from the buffer output to 1V8. I am measuring about 0,4 V at the output in that case. But if the body diode is not conducting, then how is the signal pulled down?

  • 0 in reply to Jakob Z
    Prodigy 55 points

    My bad. The P-FET source is connected to the VCC pin (which is GND in my case) and drain is connected to the output. Thus, the body diode of the P-FET is in fact conducting which is why the output if not "high" (0,4 V) in my case. Thanks for the help.