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INA181: IC overheating

Part Number: INA181

Hello,

for a bidirectional current sensing application I'm using an INA181.
I'm sensing the current in- and outflow of a leadacid-battery, so approx. 12V. As a µC I use a CC2640R2F.
I applied 3.3V to VS, ~12V to IN+ and IN- and gave it as a reference the VDDR pin of the CC2640, which is ~1.7V, the output goes directly to an analog pin of the µC.
There are two problems occuring:

1. When my board is completely switched off, but the 12V on IN+ and IN- still applied, there is a Voltage on VDDS present, which I don't want. If switched off, the board is required to carry no voltage at all  (but the 12V) .

2. After a while the INA181 heats up (you can't touch it with the finger), and eventually it broke due to overheating.

So my question is, is there anything I'm missing out on? I sticked to the datasheet as close as possible, but the INA181 shows the stated behaviour. 
Maybe using the VDDR pin of the CC2640 as a reference was a mistake, would that explain it? Any suggestions on how to make it work on the prototype?

Any help is highly appreciated, thank you. Alex

  • Hey Alexander,

    Thanks for choosing TI. We will look into this, but could you answer a couple questions. What are you using to power the INA181/VDDS? Also, what supply voltage configuration are you putting the CC2640R2F in? Basically what configuration are you choosing below?

    Sincerely,

    Peter Iliya

    Current Sensing Applications

  • Hey Alexander,

    I have a few questions for you as well.

    1. What voltage are you seeing on VDDS when it is powered off?
    2. Are you also powering off the microcontroller?
    3. Is the INA181 heating up when everything but the common mode is powered on or off?
    4. Could you send us a photo of your setup?

    Best Regards,

    Mitch M, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Peter Iliya:

    Hi Peter,
    thanks for your reply.
    To power the INA181, I'm using a LDO-Regulator 3.3V from ST "LDK320AM33R".
    The chosen supply configuration is the first one from the left (the one with the 10µH inductor).

    Regards, Alex
  • In reply to Mitch M:

    Hi Mitch,

    thank you too for your reply.
    1.) I currently desoldered the INA181, so I can't recreate the voltage, but I remember it to be something around 1.6V-1.7V, maybe ~1.3V. I'm afraid to destroy my last INA181, so unfortunately I can't come up with a more precise answer at the moment.
    2.) Yes, the µC is powered off too. Only the 12V on IN+ and IN- are applied to the INA181. The rest of the board hardware is separated via a switch from the batterie voltage.
    3.) I don't exactly understand what you mean by "common mode". The INA181 heats up, when I switch on the rest of the boardhardware. At some point I most likely had a short circuit through the INA 181, because the LDO was heating up very much as well and at some point the thermal protection triggered (shutdown at 160°C).
    4.) What exactly do you refer to by setup? My desk?;)

    Regards Alex
  • In reply to Alexander Gemmer:

    Hello Alex,

    Thank you for the information. What I mean when I ask for a picture of your setup is a picture of how you hook up your board to the supplies and battery. You don't have to turn it on or have the INA181 populated to get this picture, just tell me which voltage each supply would be set at.

    Also, could you send me you're whole schematic? That would be very helpful.

    For your information, common mode is the voltage across in+ and in-. In this case, it is your 12V.

    Best Regards,

    Mitch M, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Mitch M:

    Hi Mitch,

    my board is hooked on a laboratory DC power supply with 12V. There's not yet a batterie involved (That would be P5/BB on the schematic). As a load there's only the µC + peripherals on the board.
    As for question 3.):

    When I power the µC with the CC2640 LaunchPad via the JTAG-plug and common-mode is turned off (DC-power supply off), it didn't heat up.

    It went like this:
    As I was programming, my board powered by the LaunchPad, everything was fine. Then I switched on the DC power supply ~12V and unplugged the LaunchPad and realized a voltage on VDDS, even though the µC was switched off (SW4). I followed this and it was coming from the common mode voltage. I then desoldered the INA181 to make sure it was the reason for the voltage and it was. I stopped then looking into this matter and didn't solder the INA181 back on.

    Later I was programming a second board of the same kind which had the INA181 still soldered on. I switched on the DC power supply and everything seemed to be okay until after (I have to lie) ~5-10min my board shut off. That was when the thermal protection of the 3.3V LDO (U1) was triggered. From then on, if I switched on the board with SW4 after 2-3seconds it would shut down again. I then realized how hot the INA181 and the LDO were, desoldered the INA181 and everything was functioning fine again and the INA181 most likely gone.

    Maybe this is of help to you. Thank you for looking into this, find the schematic attached. Regards Alex

  • In reply to Alexander Gemmer:

    Hello Alex,

    It looks like you are driving the output of your LDO (U1) while powering up with the JTAG. It's possible that this is where the initial damage is coming from. Could you try powering up a board normally that you have not connected to the JTAG and see if it also is having heating/failing issues?

    Best Regards,

    Mitch M, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Mitch M:

    Hi Mitch,

    thank you for the hint. I still have one board, that I didn't connect to the JTAG, but it's not finished yet. I will check this out the next days.
    Could you please explain further what your basic assumption is, how driving the LDO on Vout could destroy the INA181, but not having any effect on the e.g. CC2640 since both are on VDDS?

    Regards, Alex
  • In reply to Alexander Gemmer:

    Hey Alex

    It's hard to know exactly what the problem is without seeing the setup and board layout. It's also possible that the devices have ESD damage, or that they got overheated during assembly. What I recommend is testing the INA181 before you put in on the board to ensure that it is working properly. This way you can know if it is a problem on the board, or a problem with the device. It would also be a good idea to measure the resistance between the various pins of the INA181 before and after you power it up. If you need more devices to test, you can request samples from the TI product page at www.ti.com/.../samplebuy.

    Best Regards,

    Mitch M, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Mitch M:

    Hi Mitch,

    I will get some more devices and do the testing you suggested. When I have more data, I'll update this thread.

    I have one more question:
    - When only common mode is powered on (in my case 12V), and no voltage applied to VS (only IN+ and IN- carry the common mode voltage), is there any voltage measurable on the Pins "OUT, VS and REF" or should it be 0V? (Assuming the device and everything else is working properly)

    If not, are there other devices with the same functionality that are completely isolated (no voltage passing through from common mode)?

    So far thank you very much for your effort, you guys are really helpful and I appreciate that a lot!
    Regards Alex

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