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TPS2492: Negative voltage tolerance at any pin

Kenji Ninagawa
Expert 4190 points
Part Number: TPS2492

Hi, Team,

 

Our customer is working on TPS2492, and has troubles for the negative voltage against serge test.

In their serge test, OUT pin is likely to have -1.3V, while their circuit has a varistor.

The DS describes in "Output Clamp Diode" in page 27 that "The OUT pin can withstand a short transient to -1V".

 

Then they have following questions;

(1) The time for -1V short transient ? (<-- no definition for the time)

(2) Judgement criteria where you permitted the "-1V" ?

(3) Could you share any data with -1.0V, -1.1V, -1.2V, -1.3V and so on if you have ?

(4) Can you allow to put Diode at GND pin in order to prevent any reverse voltage.

 

Thanks and Regards,

Metropolitan (Tokyo) Area FAE  Kenji Ninagawa

  • 0
    TI__Expert 5940 points
    Kenji,

    The OUT pin has a diode for ESD protection that can be damaged with too much energy (it is specified for HBM 2kv JEDED standard). It will start to conduct at > -0.7v. The ABS Max table lists -0.3v with no time constraint. Consider that a steady state value. We know OUT can exceed -0.3v for short periods of time (as in fault protection transients at very high load current) as long as the current is limited above -0.7v due to some output Z (R, and L) and the bypass current into the Schottky. We have tested in the lab with output Schottkys (large with Vf ~ 1v at very high current) and have had no issues during fault testing. Neither have customers. We recognize that it is almost not possible to clamp to -0.3v we have specfied in the abs max table, hence the statement in the DS mentioning -1v but recognize that current cannot be infinate. It is best to have a very strong output Schottky to clamp <1v where the diode current will be limited to safe levels by its own characteristics. These durations are typically <10usec.

    Brian
  • 0 in reply to Brian Daugherty
    TI__Expert 4190 points
    Thanks for the reply.
    The customer was convinced by the explanation.

    Then the customer has one more inquiry.

    He wants the maximum power dissipation of the internal ESD diode as a judgement criteria in case a waveform is over -1V.

    Kenji
  • 0 in reply to Kenji Ninagawa
    TI__Expert 5940 points
    Kenji,

    There isn't a power specification. It is specified to withstand the ESD energy per the HBM 2kv, 500v per CDM. At 0.3v, forward conduction should be almost 0 so it can take that indefinately.

    Brian