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ISOW7842: latch-up whenever an IO pin is active

Lindsey Fike
Intellectual 2250 points
Part Number: ISOW7842
Other Parts Discussed in Thread: LP2985

Hello, 

Posting for a customer- 

Looks like there is a latch-up whenever an IO pin is active.  When it latches, there are inrush current spikes at every 150mS for number of seconds (up to 30 seconds), then the latch-up condition goes away.

What could be causing this? 

  • 0
    TI__Genius 17100 points

    Hi Lindsey,

    Thank you for posting on E2E! By 'latch-up', are the ISOW7842 outputs not following device inputs? Can you provide waveforms of the current spikes repeating every 150ms? What is the load on Viso and is it powering on and off?

    A schematic will also be helpful, but it's possible the capacitance on Vcc might be insufficient. Please describe the latch up condition details and share insight to the questions above for confirmation.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Intellectual 2250 points

    Turns out the LDO, LP2985 that causing the inrush current spikes at every 150mS which caused the 5V to drop that then caused the reset at every 150mS.

    Could the light load (6-10mA) for this LDO that’s causing the issue?

  • 0 in reply to Lindsey Fike
    TI__Genius 17100 points

    Hi Lindsey,

    If the LDO output draws more current than the input can supply, it is expected for voltage to "dip." Is this LDO located on the primary side of ISOW or is it connected to Viso?


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points

    Hi Lindsey, all,

    This conversation is ongoing via email, but here are a few points:

    • System schematic has been shared
    • Waveforms of signal inputs and outputs, Vcc, and Viso have been requested
    • Increasing capacitance on Viso and LDO input has not improved behavior
    • Requested re-tests with a new device
    • "spikes" are observed when INA is controlled by logic (to control LDO Enable), but not when manually toggled

    Updates will continue as the thread progresses.


    Thank you,
    Manuel Chavez