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LMP8640-Q1: LMP8640 behavior when load short circuit

Zhizhao Niu
Intellectual 2315 points
Part Number: LMP8640-Q1
Other Parts Discussed in Thread: LMP8640

Hi Team,

I want to ask two questions and hope can get your help.

1. As shown in the figure, when MLCC capacitor on the Load terminal is short-circuited to ground due to the crack. Besides causing Rs to burn out, will it cause the sensor itself to fail? If it fails, what is the sensor behavior?
2. The power supply conditions are the same as above. We did experiments and found that a short circuit condition was artificially injected into the load terminal (the load terminal was M ohm high resistance before injection), and after 1s , we removed the short circuit condition, and we found that Rs was not burned and the resistance value was normal, but Vin -Change to 38V (Vin+ is still 42V at this time). How to explain this from the circuit level?  When Rs is removed, Vin- is still 38V.

Could you please help to comment on this issue? Thanks.

B.R.

Zhizhao

  • 0
    Guru 140200 points

    Hi Zhizhao,

    the differential input voltage of LMP8640 must not exceed +/-6V. See section 7.1 of datasheet. Violating this limit will destroy the LMP8640.

    The weird behaviour at the Vin- pin demonstrates that the LMP8640 is destroyed.

    Kai 

  • 0 in reply to kai klaas69
    TI__Mastermind 26475 points

    Hello Zhizhao,

    I agree with Kai that if during your short circuit you exceed any of the Absolute Max Ratings you could damage the LMP8640.  If there is damage especially in the input stage.  When this returns to normally is there a 4V drop on the 0.1Ω resistor.  Is the current running through the resistor or is this a product of the LMP8640 being damaged.

    Is 38V still at the input when the LMP8640 is removed?  I would assume when RS is installed that the voltage should still be 42V.  Please try with LMP8640 removed and with and without RS.  This will give you more information to determine the issue and what got damaged.