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Original question:

LM76202-Q1: LM76202-Q1 with ISO16750 Test A

LM76202-Q1: Load dump pulse 5a suppression

Alex Patsos
Prodigy 80 points
Part Number: LM76202-Q1
Other Parts Discussed in Thread: LM74800-Q1

I am using LM76202QPWPRQ1 as a under voltage, over voltage, forward current limiter, and ideal diode to protect power supplies in an automotive application.  The device worked as expected until an unsuppressed load dump transient (SAE J1113-11 / ISO 7637-2 pulse 5a) was applied under lab conditions.  An oscilloscope probe at the IN pins of the device indicated that peak voltage reached 62 V during the pulse, the maximum input ratings.  The LM76202-Q1 device emitted a spark during the pulse and ceased functioning.

There is a 43 V working voltage 6.6kW TVS diode in a DO-218AB package on the power line to LM76202-Q1 input.  It is capable of absorbing a large portion of the load dump transient energy, but it appears to not be able to suppress voltage low enough for LM76202-Q1 to survive such a transient.

Please provide suggestions for improved voltage suppression for LM76202-Q1 to survive load dump transients or information on alternate components that have better transient voltage immunity.

  • 0
    TI__Guru** 106251 points

    Hi Alex,

    You might need bigger TVS to suppress the voltage with in the abs max rating of LM76202-Q1. Due to dynamic impedance of the TVS diode, you will observe higher voltage than the working voltage of the TVS.

    I would suggest to consider LM74800-Q1 to handle unsuppressed load dump event. Please refer datasheet and let us know if you have any questions.

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 80 points

    Hi Rakesh,

    Thank you for the suggestions.  Part of the design requirements for the product was to be able to withstand up to 50 Vdc, otherwise a TVS diode with a clamping voltage <50 V would have been used.

    A solution was found by adding a 1 Ohm 25 W resistor between the power line and a second smaller TVS diode with the same clamping voltage at the power input to LM76202-Q1.  During a SAE J1113-11 5a pulse the voltage on the power line can go >62 V, but the second TVS diode clamps voltage to LM76202-Q1 at a steady 52 ± 1 V.  The peak power dissipation in the resistor is >100 W, but it rapidly decays after a few milliseconds.  Since the design requires the maximum current though LM76202-Q1 to be <0.5 A, this solution has a minimal impact on efficiency.

    Best Regards,

    Alex