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LM3880 FLAGx pulled up to 7VDC with 67K ohms

Mark Pieper
Expert 4650 points

The abs max on the FLAGx output is 6.0V. This design would involve pulling this up to 7.0V through a 67K ohm resistor. This would result in a very current limited pull-up bias. This 1.0V above abs max would result in a worst case bias current of 15uA through the ESD diodes, and likely less because the conduction would probably be at a voltage above 6.0V. Is this OK?

  • 0
    TI__Genius 12630 points

    Mark,

    We can't guarantee the performance of any design that uses our parts beyond the ABS MAX specs found in the datasheet. We only test our parts up to these limits and using our parts beyond these limits is at the risk of the customer. I apologize but I can't guarantee whether the design will work or not. Please let me know if you have any questions.

    Respectfully,

    Michael

  • 0 in reply to Michael_DeSando
    TI__Expert 4650 points
    Hi Michael,
    I understand the data sheet abs max shouldn't be exceeded, but this is a slightly different situation. The abs max refers to a low impedance bias applied to the pin that might result in damage primarily due to the fact that it will allow excessive current to flow, knowing that "excessive" is a relative term.
    This question refers to a very weak pull-up that effectively allows the device to establish it's own bias voltage with a known, low current. This question is really asking about the steady state current rating of the ESD protection circuits. It makes sense that at some level it would be OK to bias the output with a current that would be OK, even if the terminal voltage was above the abs max for the pin.
    - Mark
  • 0 in reply to Mark Pieper
    TI__Prodigy 220 points
    Hi Mark, you have an interesting point. To be 100% safe we know to keep below 6V absmax. Pulling up flag to 7V with 67K limiting resistor would give worse case 15uA as you state - this may be manageable but I'm not aware of any data we have in this zone which would indicate if there is any detrimental effects to lifetime or other parameters. We are definitely want to help you to use our device. Can you share more details of schematic and size of biz opportunity? (Maybe switching to email is best to get into finer details.)
    Regards, Paul