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TPS745-Q1: Inrush current check

Hsing Shen
Prodigy 190 points
Part Number: TPS745-Q1

Hi,

We use LDO TPS74501PQWDRVRQ1 in our design, Vin=5.8V / Vout=3.3V. We caught an inrush current during start-up. The max is 632mA. Can you help to check if any side-effect? Will the current damage the LDO?

Regards,

Hsing

  • 0
    TI__Genius 12345 points

    Hi Hsing, 

    What are your input and output capacitors? 

    The inrush seems somewhat odd as we would expect a shorter duration time for the inrush. The biggest concern is that it could trigger Current Limit if this duration increases. 

    It doesn't seem to be a big issue since Vout is not being pulled down. Have you verified that Vin rail doesn't see a drop? I recommend looking into the FAQ below as well as extra information:

    (+) [FAQ] Inrush Current From an LDO Perspective - Power management forum - Power management - TI E2E support forums

    Best, 

    Edgar Acosta

  • 0 in reply to Edgar Acosta1
    Prodigy 190 points

    Hi Edgar,

    Thank you for the reply. The capacitors are Cin=10UF /Cout=10UF+ 4.7UF*4pcs.

            The current becomes small after the inrush current. So, If the current limit is triggered during start-up, Vout should be back to normal(3.3V) after the inrush current. That is what I thought. If it is correct, we can accept this situation.

    Regards,

    Hsing

  • +1 in reply to Hsing Shen
    TI__Genius 12345 points

    Hi Hsing, 

    Yes, once the device recovers from current limit event (if any), then it should regulate as expected assuming there are no other issues. 

    In the case that inrush is still a concern here are some methods to reduce it:  

    • If you are enabling the device long after the input voltage is present, then increasing Cin will help lower the initial surge of current.
    • If the device enable is tied directly to the input pin, then you will look at what is powering the linear regulator to reduce the inrush
      • In this scenario, slowing down the rise time of the power source to the linear regulator will lower the inrush current
    • The device only needs 0.47uF of capacitance for stability, by reducing Cout inrush current can also be reduced. 

    Best, 

    Edgar Acosta