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TPS7A4701-EP: LDO stops working. Needs to be replaced. Why is this happening?

Scott Okuma
Prodigy 80 points
Part Number: TPS7A4701-EP

Hello,

I am currently working with the tps7a4701. Here is the schematic. 

The 28V bus is attached to a battery, which can vary from 26V to 32V. The issue we are seeing is that every once in a while the part will die. We will replace it and then about a week or so later we see it die again. Any ideas as to what might be going on?

The current being pulled is less than 0.5A. 

  • 0
    TI__Mastermind 34715 points

    Hi Scott,

    I have plenty of experience using this component under these conditions (28V battery input with similar tolerances).

    Can you provide details on the input supply transients?
    Is this straight off the 28V supply, or is there filtering between the battery and this linear regulator?

    Is this a thermal battery or other type of battery?

    Can you confirm that the battery does not go negative upon "turn on" or power being applied?

    It may be worthwhile to take some data using an oscilloscope to understand the line transients and quality of the line.

    Let me know the answers to these questions and we can continue our troubleshooting.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 80 points

    Hi Stephen,

    Thank you for your reply.

    Here are the answers to your questions:

    • Is this straight off the 28V supply, or is there filtering between the battery and this linear regulator?
      • There is a FET that does not allow the voltage to go negative. 
    • Is this a thermal battery or other type of battery?
      • It is a Li-ion
    • Can you confirm that the battery does not go negative upon "turn on" or power being applied?
      • We connected an oscilloscope to the input of the system. Upon power on the voltage drops from 32V down to 6.5V. And rises up to roughly 45V. 
      • I am starting to think that this huge upswing in voltage is what is causing our issues. I see that the absolute max for pins 15/16 is 36V. 

  • 0 in reply to Scott Okuma
    TI__Mastermind 34715 points

    Hi Scott,

    With this device, and your schematic, I would lean towards line voltage exceeding the datasheet limits as a probable issue.
    I think you have found the likely issue.
    The voltage spike hits 45V on power up.
    The component is over stressed but it appears to be not enough to immediately result in device failure.
    Rather, it takes a week for the device to completely fail.

    If you need us to find a component which can withstand a higher voltage (45V?), let me know and I can have one of our marketing experts provide some feedback to this forum post.

    Or, I would look for a way to prevent the over voltage from entering the LDO.
    If the 45V is a fast transient (faster than perhaps a milisecond) then one option is to use your FET as a load switch, and to soft start the input to the LDO if this is not already being done.

    I hope this helps.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 80 points

    Stephen,

    Thank you for your reply. We are currently implementing clamping circuitry to keep the voltage below 34V. 

    I am curious about a component that can with stand a higher voltage. If you can recommend one we may go with that for future use. 

    Thank you for your time,

    -Scott