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LM5177: Failure mode to ensure PELV system

Søren Larsen
Prodigy 60 points
Part Number: LM5177
Other Parts Discussed in Thread: , LM5176

Tool/software:

Hi Ti,

I am working on an application that is powered by a battery source (22V-57V). In this design, I intend to implement a buck-boost converter using the LM5177.

To comply with PELV (Protective Extra-Low Voltage) system requirements, I need to ensure that the output voltage of the LM5177 does not exceed 60V, in the event of a single fault in the LM5177.

Could you please provide insights on:

  1. The potential failure modes of the LM5177?
  2. How to ensure that Vout remains within the 60V limit under fault conditions?

Thank you.

Best regards,
Soeren

  • +1
    TI__Mastermind 49951 points

    Hi Soren,

    VT+(OVP) is the overvoltage protection which is related to the FB pin - therefore a fault on the FB divider could not be detected here.

    The LM5177 has an additional overvoltage protection on the output which is set to 86V  VT+(OVP2) .

    This is fixed and can not be adjusted.

    So in this case an external circuit would be required for that protection, e.g. be disabling the LM5177 if VOUT > 60V.

    The LM51772 would allow to adjust this value but the abs max rating for this device is 55V.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 60 points

    Hi Stefan,

    Thank you for your replay. I can see that I need external protection circuit.
    Do you have any safety related data like FIT and failure modes for the LM5177 as you do for the LM5176?

    Talking about the LM5176, one of the failure modes is "Output not in specification – voltage or timing ".
    What voltage range can be expected on the output if this failure happens?


    Best regards,
    Soren

  • 0 in reply to Søren Larsen
    TI__Mastermind 49951 points

    Hi Soren,

    FIT data for the LM5177 is planned but not ready now.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 60 points

    Hi Stefen,
    Good to hear. Thank you for your quick reply.