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LP2992-3.3V OFF state Input to Output feedthru

TonyMCC
Intellectual 750 points
Other Parts Discussed in Thread: LP2992

I have the LP2992AIM5-3.3V On/Off pin #3 connected to ground thru a 10k resistor. This puts the device in the OFF state. If I apply 5V at the input while the device is in the OFF state, I measure 1.32V at the output. Is this expected behavior ?

What is the expected input to output isolation or feed-thru for this device when it is in OFF state ?

Thanks.

  • 0
    TI__Prodigy 160 points

    HI tony,  what's is the loading condition of the output?

    I checked LP2992 datasheet, looks like it does not has auto-discharge function.

    if there are no loading there, even when you disabled the device, the output capacitor will became floating, and you might see a random voltage value on it.

    Hope this will help you.

  • 0 in reply to Ying,Jonathan(SH)
    Intellectual 750 points

    The LP2992 is normally powering an FPGA device.

    I added a 5k resistive load to the Vout pin and it is still producing about 1.36V while OFF = 0V and 5V is being applied to Vin.

    Tony

  • 0 in reply to TonyMCC
    TI__Prodigy 160 points

    From datasheet Figure 35., we can clearly see Vout should drop to 0-V when turning off the LP2992 , don't know where 1.36V comes from.

    Here is my suggestions:

    1. Turn on the LP2992, then check Vout conditions, to see if it a stable 3.3V, make sure the device works correctly.

    2. Turn off the LP2992, waited a while(e.g. 1 second), then check if the Vout is still 1.36V. if yes, Try to disconnect LP2992 from FPGA, then check if Vout drop to 0-V.

  • 0 in reply to Ying,Jonathan(SH)
    Intellectual 750 points

    When I isolate the LP2992 from FPGA it seems to be working...its output changes from 0V to 3.3V as expected with no intermediate 1.3V state. I believe the issue may be the LP2992 is being backdriven from the FPGA during the power on sequence of the board. We will investigate the power on sequence further.

    Thanks.