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TPS7A49: Absoulte maximum ratings: OUT pin to IN pin voltage

Part Number: TPS7A49
Other Parts Discussed in Thread: TPS7A30-49EVM-567,

The datasheet of the LDO TPS7a49 specifies a limit of -36 ... 0.3V for the OUT pin to IN pin voltage. I am using the regulator with a relatively large output capacitance of 1mF and when I turn off the IN voltage of the LDO (EN is connected to IN), said limit is not met because the output capacitance discharges slower than the input net. I can see the same behaviour on the evaluation module TPS7A30-49EVM-567 after disconnecting the input voltage.

Can this behaviour destroy the regulator?

Are there any countermeasures that could be taken?

  • Hi Simon,

    When Vout exceeds Vin, there is the potential for reverse current to flow.  TPS7A49 does not have any internal reverse current protection circuitry.  As such, any reverse current will not be limited and could damage the LDO.  

    Since reverse current can occur in your application, external circuitry should be added.  Commonly a Schottky diode placed from OUT to IN in parallel with the LDO in order to provide a robust path for the reverse current.  Schottky diodes fit this use due to their low forward voltage.

    It is important to note that this method will protect the LDO from the reverse current; however, it will not prevent the reverse current from continuing upstream.  If you need this protection, a diode placed before the input capacitor of the LDO will block the reverse current from proceeding upstream.  You will need to make sure that you have enough headroom in your application in order to satisfy the dropout requirements for the LDO with the voltage drop across the diode.

    Very Respectfully,

    Ryan

  • Hi Ryan

    Thank you for your answer. This clarifies my question.

    Best regards

    Simon