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INA190: IN190 Current Path Between IN- and GND.

Alexander Doknjas
Prodigy 40 points
Part Number: INA190

Hello,

I have found a weird issue with one of our products. Please see simplified schematic. I will do my best to explain the steps to make this issue occur. We are using a INA190A1 to monitor the bi-directional current on a battery pack. The product has a low-side power switch to disconnect the battery pack from the rest of the product during shipping and transport. Here is the issue:

1.) The battery charger is connected to J1.
2.) Low side power switch S1 is closed, connecting the battery charger to the battery.
3.) Battery begins to charge. 3V3_BAT is 0 V, as the product has not turned on and started to regulate 3V3_BAT. The only thing "on" is battery which is charging.
4.) If S1 is opened and the charger disconnected, a voltage is still present across J1 (PACK_P and GND). The voltage is about 500 mV less than the battery voltage. Attaching a 0.5 A load across PACK_P and GND sinks current out of the battery, and U1 gets extremely hot in a short period of time.
5.) The only way to remove the voltage present across PACK_P and GND is to physically remove the battery from the battery pack. Inserting the battery once removed brings it back to the default condition of 0 V.

We are planning on changing this design so that U1 is on the high side of the battery, but I would like to know why this potential current path between IN- and GND exists on the INA190.

Thanks,


Alex

  • 0
    Guru 140200 points

    Hi Alexander,

    I think the current is flowing this way

    and by this violating the absolute maximum ratings of INA190 referring to the common mode input voltage range. The inputs of INA190 become negative relative to the GND pin, by just the 500mV decrease of battery voltage you observe!

    Kai

  • +1
    TI__Mastermind 26620 points

    Hey Alex,

    Our apologies for the delayed response.

    This definitely seems like a VCM < -0.3V violation occurring where ESD cells' body diodes are becoming forward biased (current flowing out of the input pins). Once forward biased with > 5mA of current, the device could already become damaged causing the input pins to become low impedance and sink significant current and become hot.

    My suggestions are to start with a new/fresh system/INA190 device to make sure you are testing with something that is not broken and try the following:

    1. In step 4, can you disconnect the charger from J1 first before opening S1?

    2.  Try modifying PCB so that INA190 GND pin is no connected to the "GND" node, but rather the battery negative terminal. 

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    Prodigy 40 points

    Hi Peter,

    I had some time to investigate the issue further:

    1.) Disconnecting the charger from J1 before opening S1 does not appear to solve the issue.
    2.) A fresh INA190 with the GND pin shorted to the GND node all the time works and does not cause any issue.

    I tested this configuration with just shorting everything that is GND referenced on the battery pack to PACK_N. While the INA190 worked fine, it caused some weird issues with another sensor once PACK_N was disconnected (S1 opened). I moved the INA190 to sense the high side of the battery (R1 moved to series between BAT_P and PACK_P), and kept its GND pins connected to GND and not PACK_N. This configuration appears to work perfectly fine and it fixes the weird voltage levels from the other sensor.

    I think I will move forwards with this configuration.

    Thanks for your help,


    Alex

  • 0 in reply to Alexander Doknjas
    TI__Mastermind 26620 points

    Hey Alex,

    Good to hear. Referencing the amplifier ground to battery negative terminal is safest way to use INA190 so when the pack is disconnected from battery, there is no ground loop that could damage device. When battery is discharging/charging, as long as the PACK_N and GND are connected with low-impedance trace/cable, then INA190 will be able to drive accurate output voltage for downstream ADC.

    Let us know if you have any other questions.

    Best,

    Peter