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high current sink from IN+ / IN- during hot-plug

luca buccolini
Prodigy 130 points
Part Number: INA229-Q1
Other Parts Discussed in Thread: INA229

Dear TI,

I've a strange behaviour with INA229 during hot plug of connector of our BMS.

We noticed that the series resistors R179 and R180 of the differential sensing line IN+ and IN- changes their values to kohms due to a fault. After this breakdown, the INA229 measure bad currents but it seems it still works (by replacing the resistors it returns to measure correctly).

From the image below, you can see the voltage drop across the resistor R180 during the connection of the power connector of our BMS.

The voltage of the O-scope is Vab when the R180 and R179 resistor was replaced with 120ohm resistors thus a current > 24V/120ohm=200mA flows into R180 burning it. The same probably occours to R179.

This happends only if we connect the power connector ( the connector that supply power and GND to the BMS) after the connector with the sensing pins (AI_SHUNT_P and AI_SHUNT_N) connected to the shunt resistors (in low side).

Why this happened?

How can I solve this isse?

Thank you.

  • 0
    TI__Mastermind 26465 points

    Hello Luca,

    Thank you for using the TI forum. Here is a link to a video that explains the error associated with an input filter: https://www.ti.com/video/6219017476001

    For this device in order to avoid too much error, you need to make sure that R179 and R180 are below 100Ω and that they are closely matched to each other.

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Prodigy 130 points

    Hello Mitch,

    thank you for the hints about the error in the input filter.

    I'm currently involved to solve the problem due to the high-current into the IN and IN- pins during connectioon event of GND and power supply. This current burns the resistors either if are mounted the 51ohm and if are mounted the120ohm. I just reported the screenshoot of the o-scope when the 120ohm was mounted into R179 and R180 designators because at that moment I had not any 51ohm resistor available.

    Is there any action I can do to prevent this high-currents on the IN+/IN- pin during plug-in of the INA229 power supply connector?

  • 0 in reply to luca buccolini
    TI__Mastermind 26465 points

    Hello Luca,

    I have seen that some people use ferrite beads to help with this, although the specs need to be checked to help make sure it does not affect accuracy too much. Similarly, using much larger resistors could help with the high currents, but that is not recommended as it could lower measurement accuracy.  It may be a good idea to better understand why this is happening. I see that there are 2 grounds, so it would be a good idea to double check that there is not a grounding issue. Also, if nothing else is working, then changing to high side sensing may help.

    Regards,

    Mitch