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TPS7A8101: TPS7A8101 output before Enable

Part Number: TPS7A8101

Hi Team,

My customer is evaluating our TPS7A8101. Below is the start-up(VIN, Vout, Enable) waveform also showed below:

The issue is described as below:

When Vin=5V was give(Showed in waveform, the Yellow curve), after delay about 500ms, then pull the Enable high(Pink curve), but before the Enable become high, these is Vout=0.7V, but not about 0V. This will cause problem for customer to use.

So why TPS7A8101 has output before Enable the device? Any solution to avoid this issue? Thanks.

Best regards,

Sulyn

  • Hi Sulyn,

    As with most LDOs, TPS7A8101 does not have an active pulldown on the output. As such the first thing we should check in debugging is if the output is being externally biased. If an external bias is present, the LDO does not have a way to pull the rail back down to GND.

    Does the input to TPS7A8101 also power any other devices in the circuit? Often in devices that have multiple input rails, a higher rail can actually bias a lower rail through the device itself. Often this bias path is through the ESD protection.

    Very Respectfully,
    Ryan
  • Hi Ryan,

    Thanks for your support! These is no other thing on Vout, just the feedback resistor as showed in below schematic.


    So the question is if Vout floated, TPS7A8101 will output about 0v when Enable not pulled high?

    Best regards,

    Sulyn

  • Hi Sulyn,

    LDOs cannot boost voltage so if Vin is floating and a voltage is observed on the output of the LDO regardless of the state of EN, there is a leakage path biasing the output of the LDO.

    With the LDO isolated (the load is removed) the output is still biased high when Vin = 5 V and EN = 0 V? If so, we need to look for other unintentional leakage paths such as residual flux on the board that may be allowing the output to be biased.

    Very Respectfully,
    Ryan
  • Hi Sulyn,

    Since I have not heard back from you, I am assuming that you were able to resolve your issue. If not, please post a reply below (or create a now thread if this thread has locked due to time out).

    Very Respectfully,
    Ryan