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SN74AVC32T245 damaged by latch-up?

Peter West1
Prodigy 60 points
Other Parts Discussed in Thread: SN74AVC32T245

We have an excess current problem affecting a large percentage of our products. The SN74AVC32T245 we use to translate between the 1V8 bus of our DSP chip and the 3V3 bus of an SD host controller chip appears to be drawing an amount of current up to 50mA.

The current varies from unit to unit but each unit is stable at a particular current draw. This additional current draw  is remarkably stable across active and hibernate modes of the unit . If the 32T245 is removed the current drops by at least 2/3 and if a new device is fitted the current draw will also generally drop.

Is it possible the device could have been damaged, e.g. by latch-up, during the power on sequence of the device? Unfortunately our circuit does not contain the nOE pull-ups recommended in the data sheet.

Pete.

  • 0
    TI__Expert 6430 points

    Hi Peter,

    From your description, I cannot figour out the cause. Could you give some information about your system. It will be helpful.

    1, Is 50mA current drop on VCCA or VCCB?

    2 Dose 50mA current hold on if it happened?

    3 Dose translator function work normaly when 50mA current drop happened?

    4 Are the input signals are floating status when  50mA current drop happened?

    Thanks

    Wei

  • 0 in reply to Wei Lang
    Prodigy 60 points

    Hi Wei,

    Thanks for your response. My answers:

    1. It appears to be mostly from VCCB.

    2. The excess current is present in all modes of the product, active and idle.

    3. Yes.

    4. The current is present regardless of the input state. There certainly may be moments where the inputs are floating.

    Best regards,

    Peter.

  • 0 in reply to Peter West1
    TI__Genius 17270 points

    Hello Peter,

    As the excess current draw is from VCCB and the B side I/Os are connected to the SDIO ports, this makes me think that the B side inputs could be  floating by the High-Z state of U29 causing high current draw.

    Best regards,

    MRC

  • 0 in reply to Mizanur Chowdhury
    Prodigy 60 points

    Hi MRC,

    Thanks.

    Is an input floating near the threshold a problem only when nOE is low or in both low and high cases?

    How do you account for the fact the the excess current remains constant whether the unit is active (no floating inputs) or idle (perhaps floating inputs)? Does this indicate the device has been damaged by an earlier floating input event - could it really be that easy to damage it in your experience?

    Best regards,

    Peter.