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TPS7A4701-EP: damaged during back-feeding

Michael T Schneider
Expert 3780 points
Part Number: TPS7A4701-EP

Can the TPS7A4701-EP linear regulator be damaged under the following conditions:

  1. Back-feeding a 3.3 Vdc voltage source at the linear regulator’s output if there is no 5 Vdc input voltage source.
  2. Back-feeding a 3.3 Vdc voltage source at the linear regulator’s output if the linear regulator is already operational with a 5 Vdc input voltage source.

 

The linear regulator has been setup with a feedback resistor string at pin 3 to establish an output voltage of 3.3 Vdc.

The other pins 4-6, & 8-12 are left floating. 

 

Also, we inadvertently shorted the output to return (GND).  Please confirm that the linear regulator then would not be damaged with its current limit and thermal shutdown kicking in.  It’s designed that way as stated in the data sheet.

 

I also have some concerns regarding the feedback control scheme being affected with the two conditions stated above.  Would there have been some stability issues with the above two conditions that may have resulted in an unstable operation which then may have affected the linear regulator? 

  • 0
    TI__Mastermind 38195 points

    Hi Michael,

    It is not clear in the datasheet whether this device can withstand a reverse voltage because the abs max spec for the output voltage is only related to GND and there is no mention anywhere of reverse current or voltage protection. My guess would be that it cannot withstand 3.3V on the output when the 5V supply is not connected, but I cannot be sure without testing it. I've ordered an EVM because we do not have one in the office, and it should be here early next week. I'll let you know when I am able to test it.

    Regards,

    Nick

  • 0
    TI__Mastermind 38195 points

    Hi Michael,

    I suppose I can answer the other questions for now.

    The device can survive the output being shorted to GND; as they mentioned, the device will cycle in and out of thermal shutdown until the short is removed. Operating like this for very long degrades the lifetime of the device so it is not advised to allow this to go on for long. 

    My understanding of the other question is that each of the conditions stated above are applied and then removed and normal operation resumes; i.e. the input voltage is 5V and there is no forced voltage (3.3V or something else) at the output. In this case, if the device was not damaged during these conditions, device stability is not affected. However, stability will not be a concern if the device is damaged by these conditions anyways.

    Regards,

    Nick