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LMP8480: Inverse polarity protection

Part Number: LMP8480

Hello

I have a design where I use a LMP8480 to measure the charge current from a charger to a battery with this schematic. The problem is, if I invert the wires connected to the outputs of the charger, LMP8480 is destroyed. 

I have put a diode in the place of R211 with the same result. Is there any solution to avoid a damage in the component in case of a invert connection?

Thank you very much

Israel

  • Hi Israel,

    What is the part number of the diode you tried?

    There are a few options. The simplest is probably to stick to your original design. Assuming what you have is a 12V charger (can you confirm?), I would increase R211 to about 2K Ohms. The drawback is that the amplifier will lose some headroom, depending on your requirements for output voltage level, it might be OK since the current draw is small (<155uA). Please experiment with it. If LMP8480 survives, then I would do a functionality check to see if there is impact on performance that is unacceptable to your application.

    Alternatively I think the diode approach still might work, but it is important to choose an appropriate one that can withstand the reverse voltage. A series resistor is still a good idea however for current limiting just in case.

    Or a reverse polarity protection circuit can be incorporated with FET controllers such as LM5050. There is such example circuit in the datasheet that you can probably adapt fairly easily.

    Finally, I see you have three electrolytic capacitors. I would replace them with ceramic capacitors.

    Regards, Guang

  • Hello Guang

    Thank you for your response. I have put a resistor of 4k7 in R211 and the result is the damaged of R216 and R215 resistors. I think also LMP8480.

    The diode I have put in last test was a LS4148 with a reverse voltage of 75V.

    All the capacitors are ceramic.

    Perhaps putting a diode between GND pin and GND?

    Thanks

  • Hi Israel,

    Yes, I think a ground diode will protect LMP8480. You’ll have to consider/account for the voltage drop when measuring the output voltage.

    If R215 and R216 are increased equally as R211, LMP8480 should survive as well. However the higher resistor value will have negative impact on the system gain error.

    Regards, Guang

  • Hello Guang

    I have put a diode between GND pin and GND and it doesn't protect.

    Finally I have resolved putting a PTC between GND and GND pin.

    The PTC is MF-MSM030-2 (Bourns)

    The current measurements are correct with this PTC.

    Thanks

    Israel