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TPS2640: IMON resistor referenced to GND

chris padbury
Prodigy 70 points
Part Number: TPS2640

Tool/software:

In Section 10.4 of the datasheet it says not to connect RTN to GND (disables reverse polarity protection feature) and that IMON resistor should be connected with respect to RTN pin. In our design we connected a resistor between the IMON pin and GND since the ADC references GND. (NB: We have 100k of resistance between the IMON pin and the ADC circuitry as recommended in Section 9.3.5.4) . Is it OK to have a resistor between the IMON pin and GND, rather than RTN, without compromising the reverse polarity protection or any of the other protection features. If this is not ideal, can you please provide a minimum resistance above which it is OK and we can adjust the resistor since we are trying to avoid a copper change to our PCB.

For reference, we are currently using a 1k resistor but intend to increase that to either 5.1k or 51k.

For the avoidance of doubt, RTN is not connected to GND.

  • 0
    TI__Mastermind 30681 points

    Hello Chris,

    For reverse polarity protection, IMON needs to be connected to RTN. In case of reverse polarity RTN and GND are separated.

    In that case it's more resistance the better to limit the current. But negative voltage will violate the pin abs max voltage.

    I would recommend connecting it to RTN.

    Thanks

    Amrit 

  • 0 in reply to Amrit Jit
    Prodigy 70 points
    Amrit Jit said:
    For reverse polarity protection, IMON needs to be connected to RTN.

    IMON can be left floating as well I believe.

    In our application, we don't actually need the reverse polarity protection, but we do need reverse current protection, OVP and circuit breaker current limiting. Does that mean we are OK to connect the IMON resistor to GND?

  • +1 in reply to chris padbury
    TI__Mastermind 30681 points

    Hello Chris,

    In that case, yes IMON can be connected to GND. 

    Reverse current blocking will work even if you connect RTN to GND. Only reverse polarity will be disabled.

    Thanks 

    Amrit