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INA381: As a simple On/Off indicator?

Terry Phillips1
Prodigy 20 points
Part Number: INA381
Other Parts Discussed in Thread: INA181

Greetings - I have a need to sense a 12vdc 3w lamp circuit (non-automotive) to see if the lamp is on or off. Not that I think it's important but the lamp can be in a flashing state with a frequency measured in many seconds. It's an existing piece of hardware that sinks the voltage to ground via IC, not mechanical. The "monitoring" will be accomplished by a mcu GPIO @ 3.3v. Tapping into the existing wiring is my only option, preferably after the lamp, as there are 2 lamps sharing a common 12vdc wire. I realize this this is a stretch outside the realm of an INA381 intended application, just more a curiosity if it possible and if so, would the INA381 accomplish the task?

TIA,

-Terry

  • 0
    Guru 140200 points

    Hi Terry,

    section 7.3.1 of datasheet shows that it's possible to work with a low side Rsense. So, this should work.

    Where do you see issues?

    Kai

  • 0
    TI__Mastermind 32395 points

    Hello Terry,

    This should be very easy to accomplish with the INA381 as this current-sense amplifier can operate high-side (VCM>Vs) or low-side (VCM=0V), where VCM is input common-mode voltage. Do you need the comparator to drive a binary signal into MCU? This is a typical application of the INA381 where the shunt voltage is amplifier and routed to the comparator input. The comparator reference will need to be generated with a resistor divider off Vs or separate external voltage source. Or you could drive the MCU ADC with the analog OUT signal and determine ON/OFF by comparing the digital reading with a value set in firmware memory. In this case, the comparator is not needed and you can just use the INA181, which essentially the same but without the internal comparator.

    Depending where the INA381 is positioned (before or after the low-side switch "IC"), there could be some AC CMRR disturbance on the output due to the VCM of INA381 switching from 12V to 0V quickly. This would need to be tested, but easily mitigated given how slow the lamp switches and only needing to determine ON or OFF.

    Best,

    Peter

  • 0 in reply to Peter Iliya
    Prodigy 20 points

    Thank you Peter and Kai for the confirmation. I have a couple pieces in the mail and look forward to working with them. Peter to your point for this application I don't really care how much current, just simply that there is current flowing. But I do have both ADC channels and AC functionality available so we'll see what other uses I can make of them...

    Best regards,

    -Terry