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LM74900-Q1: Load dump Reverse voltage protection function Test mesthod

Chul Kim
Intellectual 260 points

Part Number: LM74900-Q1

Hi all

I am currently testing a reverse voltage protection feature on a load dump (LM74900q1).
I am applying a reverse voltage to the V_bat input and checking the output voltage (VIN) for abnormalities and Dgate pulled low.

The expectation is as shown in the figure below.

However, when I applied reverse voltage to V_bat net using Power supply,
The reverse current flows and the power supply shows CC, so the reverse voltage is not applied.
For example, if you apply -14V using the power supply, the power supply CC will only drop about -2V.

There does not appear to be a path for reverse current to flow in the figure below. 

Is there anything that could possibly cause reverse current to flow?

I would like to know how to test the reverse voltage protection function using the power supply in a diagrammatic sequence.

Thank you. 

  • 0
    TI__Guru 57737 points

    Hi Chul Kim,

    Normal bench top power supplies which supplies positive voltage can be used to apply reverse voltage at the input. Just connect the positive terminal of the power supply output to the GND terminal for the LM74900-Q1 and connect the '-' or the GND terminal of the power supply output to the Vin  of the LM74900-Q1.