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  • TI Thinks Resolved

INA826: Instrumention Amplifier gets damaged

Part Number: INA826

Hello,

i am developing an constant current source. The following picture shows the concept.

The current is given by dividing the DA-Converter-Voltage with one of the resistor values (SHUNTS). Which resistor is activated is controlled by an microcontroller. Also the DA-Voltage ist controlled by the microcontroller. The Current flows through P$1. The INA826 has a supply voltage of 30 V DC, Rg is not connected, so the gain is 1. Pin 4 of the INA826 is allways connected to 30V. Pin 1 varies between 28 and 30 V. That means the maximum output voltage is 2 V. 

Now the Problem: The INA826 gets allways damaged. I cant explain why. I tried other Instrumentation Amplifiers from other companies at the same conditions and it worked fine. Also I tried the INA828 and it gets damaged too. As soon as voltage is turned on, the INA826 blows. I damaged allmost 10 devices. 

Is something wrong with the wiring of the INA826?

  • Hi Peter,
    Your circuit looks okay to me. If there's an issue where excessive voltage appears at the inputs of the INA826, you can add a series resistance (say 1k to 10k) which will limit the current into those pins.

    Also, while not related to your issue, it's a good idea to configure the second amplifier in U4 to be a buffer (pin 6 to pin 7) and tie its input to a known voltage - typically mid-supply.

    What was the failure mode you observed? That may help narrow down a cause.

    Regards,

    Alex Davis

    Precision Amplifier Applications - TI Tucson

  • In reply to Alexander Davis:

    I dont think that the inputs are the problems. The data sheet says that they are protected up to 40 V. I tried the resistor in series to the inputs before.  

    There were some moments when the circuit works like expected with the INA826. But that didnt work long. After a day I turned the circuit on in got damaged again. I also tried to work only with the INA826 and test it. First it worked fine but after a time it just blows, without doing something. 

    The device gets really hot and starts to smoke.

  • In reply to Peter Simon Terentschenko:

    Hi Peter,

    That's a pretty catastrophic failure. While it's possible that there's an issue with the PCB, I think that's unlikely, since it does work sometimes. What I suspect is more likely is a latchup event, possibly being caused by the power supply itself. If the power supply overshoots above the INA826's max supply voltage, it's possible it could be triggering an ESD structure which then latches on until the amplifier is destroyed. To eliminate that possibility, you could add an appropriately rated TVS diode (say 33V or so, depending on your typical supply voltages) across the supply pins of the INA826. That would act as a first line of defense and clamp the supply before damage to the INA826 occurred.

    On a second look at the schematic, it's possible that at low current levels, you may be violating both the input common mode range and output swing capabilities of the INA826, but without knowing your current ranges, I can't say for sure. 

    Regards,

    Alex Davis

    Precision Amplifier Applications - TI Tucson

  • In reply to Alexander Davis:

    Thanks, I will try the TSV-Diode later.
    The current ranges are between 10 µA and 100 mA
  • In reply to Peter Simon Terentschenko:

    Hi Peter,

    I misspoke somewhat in my previous reply. In any given range, what is the minimum output current you expect to provide? The common mode seen at the inputs of the INA826 will be 15*(2 - iout * Rshunt). We provide a calculator tool here which calculates the available output swing for an instrumentation amplifier based on common mode voltage, supplies, gain, and reference voltage. This may be useful to ensure that the INA works well in your application. 

    Regards,

    Alex Davis

    Precision Amplifier Applications - TI Tucson

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