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INA210: Extremally high bias current when VCC > Common Mode voltage

Part Number: INA210
Other Parts Discussed in Thread: INA226

Hello,

I am using INA210  in several places of my design normally when common mode voltage on IN+, IN- is lower than V+=5V all these circuits works great.. In one place however I use INA210 with common mode volage of 12V while V+=5V.

In this case I have observed extremally high IN+ current =550uA while IN- current is only 41uA. My output (OUT) saturates to 5V. I am aware that bias current is asymetrical but was under impression it does not go to hundreds of uA

Is my observation correct , are you expecting such a big difference, and big value of IN+ bias current?

On the very same shunt resistor (effectively in parallel with INA210) I also have INA226 doing remote sensing and once I isolate INA 210 ( which primary function is to provide single ended voltage for multimeter measurements ) INA 226 works as a charm with very small bias currents.

Do you expect INA226 to behave much better .

I expect you would say that 550uA of bias is possible but in such a case I will have to give up on INA 210  so is it ok to leave it's inputs floating ?

Thank you very much for your help

Sebastian

  • Hi Sebatian,

    hmm, 550µA is a bit high. Maybe the INA210 got damaged? Can you exclude overvoltage events at the inputs?

    Can you show a schematic? And what about the floating inputs? Can you explain in detail?

    Kai

  • Hello Kai, thanls for help.

    It is a great suggestion I will lower the voltage and try if INA210 starts behaving resonably.

    Can you refresh my memor on the way of passing yiou teh schematic, was it privet message, how to do do?

    Guess schermatic will explain floating inputs , I have two serial resistors of 0 ohm on inputs to INA210 so I can just lift them off.

    Sebastian

  • Hello Sebastian,

    I agree with Kai that the device could have gotten damaged.  If it is damaged I would not trust it at any voltage.  Is there any way the input could have experienced an over voltage event like Kai mentioned.  Is this happening on your setup for all INA210 installed or is it just this one device.  I will share how you can share your schematic.

  • Hell Javier,

    Thank you for your inut , I tend to agree that it might get damaged, though I right nw have no idea why and how. The shunt resistor is on input to board power suply  (12 V) . This is first board which came from manufacturing so everything can be possible ( including wrong part fit, but since other INAs are working fine I guess this is less likely) On monday I should get another board so I will try to see if the situation is one off .I guess to damage the device you need some serious voltages ( 26 V ) and tehre is no way it could have happened unles through ESD.

    I have run some measurements on the one I have and I got :

    Ucommon     Iin+      Iin-

    12                   446u    10u

    7                     143u     0u 

    5.1                    82u     0u

    Output stuck at 5V

    I will come back to you on monday.

  • Hi Sebastian,

    think also of inductive kick back. Has the load an inductive component? Is there any cabling?

    I would always protect the inputs with TVS as discussed in section 7.4.4 of datasheet.

    Kai

  • No, load is actuall a test point , so effectively no load.

    Yes inputs are not protected and this looks like there is a need for it. I have shared schematics with Javier.

    Sebastian

  • Hello Javier , Kai,

    I have another board back from factory , and the INA210 still behaves strange.

    Good thng is, that the output is not stuck at 5V.

    If UCMM=12V:

    U shunt=0.818mV

    U+ - U- =-0.17mV ( on input sof INA210) Yes it is negative.

    Udrop on positive track from shunt to IN+= 1.022mV

    Udrop on negative track from shunt to IN-= 0.02mV

    U out= 3.086mV

    ( resitsance of tracks from shunt to INA210 inputs is approx 0.8ohm, so you can see the bias currents , I+=1.27mA, I- = 25uA)

    If I lower UCMM=5.5V

    U shunt=1.455mV

    U+ - U- =1.280mV

    Udrop on positive track from shunt to IN+= 0.185mV

    Udrop on negative track from shunt to IN-= 0.015mV

    U out = 0.256V

    I guess ESD is excluded as INA210 works fine with UCMM= 5.5V but at 12 V it looks strange.

    What do you think?

    Sebastian

  • Sebastian,

    It still does not look like what I would expect.  I don't expect that much current running through the input so the INA210 IN+.  We are missing something.  I am looking over the schematic some more and I will get back to you tomorrow if I come up with something.  In the mean time below are some of my thought I know some are repeated.

    Did you say that the INA226 measures the correct voltage?  I would expect both to measure similar voltages and the voltage at the inputs should be the same.  The thing seems to be that the input resistors to the INA210 are not 0Ω but you measured 0.8Ω.  That is still high for a trace and a 0 Ω resistor.

    Also please double check the connections between grounds.  You should actually measure the voltage between to two different grounds.  I know I have made that mistake myself.

  • Thank you for your help Javier, will wait for your suggestions.

    The Ina 226 indeed measures correct voltage , even the negative one .

    The trace resistance is indeed 0.8R and it is understood. Will explain.

    This INA226, measures voltage from different place on the board, and this voltage measurement ( 0.8V) is the prime reason for having INA226. Now since INA226 has additional option to measure current , instead of leaving it unconnected I came up with an idea of using current measurement feature to measure board input current but this involves long traces ( voltage is primary function). The 0.8R resistance is what I have measured and it is consistent with CAD tool report of 0.676R ( to certain level of precision but I agree it will be around 0.7R, though this makes current even bigger). O ohm resistors right now are just pieces of soldered wire. The INA 210 sits there as a backup option to measure current using multimeter.

    I am not sure on the suggestion for GND connections , you asking if it exists? If so yes it does and  has around 40mR . Voltage wise : 330uV drop between grounds. It does not change much with UCCM at 5.2V the drop is 228uV.

    I am not sure on the impact on current measurement of the ground difference though, but for voltage measurements it will add to error.

     

    Sebastian

  • Sebastian,

    I was able to get in the lab with some INA210EVM and I got the results expected.  I tested 2 INA210 and got similar results.  I think there is something if your setup that may be pulling current that you are not expecting.  I have attached my data below.

    Device Vs (V) VCM (V) Vsense(mV) IB+ (µA) IB- (µA) Vout (V)
    1 5 5 0 22.4 22.4 0.0023
    1 5 5 1 23.8 22.8 0.1991
    1 5 5 20 50.3 30.7 3.998
    1 5 5 50 92 47.9 5
    1 5 5 100 161.8 78.3 5
    1 5 12 0 29.1 29.1 0.00316
    1 5 12 1 30.5 29.6 0.1994
    1 5 12 20 57 37.5 3.998
    1 5 12 50 98.7 54.7 5
    1 5 12 100 168.5 85 5
    1 5 24 0 40.9 40.9 0.00496
    1 5 24 1 42.3 41.4 0.19999
    1 5 24 20 68.8 49.3 3.998
    1 5 24 50 110.6 66.5 5
    1 5 24 100 180.4 96.9 5
    2 5 5 0 23.4 23.4 0.00256
    2 5 5 1 24.8 23.8 0.1993
    2 5 5 20 51.5 31.4 3.9979
    2 5 5 50 93.6 48.3 5
    2 5 5 100 163.9 78.1 5
    2 5 12 0 30.4 30.4 0.0034
    2 5 12 1 31.7 30.7 0.1994
    2 5 12 20 58.4 38.4 3.998
    2 5 12 50 100.5 55.3 5
    2 5 12 100 170.8 85.1 5
    2 5 24 0 42.6 42.6 0.0053
    2 5 24 1 44.1 43 0.1996
    2 5 24 20 70.7 50.7 3.9981
    2 5 24 50 112.9 67.6 5
    2 5 24 100 183.1 97.4 5
  • Hello Javier,

    Thank you very much for your data  and engagement.

    It is puzzling, as from the schematic you see there are not many things which could pull the current.

    The only explanantion i can come up with is the sequence of power supply.

    In my case I am, getting Vin+=12V , then Vin-=12V , then Vs =5V.

    Is there a chance to see if in this situation the currents will be similar.

    Thanks

    Sebastian

  • Hi Sebatsian,

    do you get proper results, if you power up the INA210 first?

    Kai

  • Hello Kai,

    Unfortunatelly I am not able to power up INA210 first , I have relied on teh data sheet saying teh voltage order does not matter so it should work but thi sis the only place I can pinpoint to .

    Sebastoan

  • Sebastian,

    I can attempt this but it will be a day or two delay as I am not going into the office as regular due to current conditions.  I will verify the data but I do not think I will see a difference.

  • Hello Javier,

    Literally now I had some more news on the subject.I have received two more boards from production and both working fine!

    approx 25uA bias current.

    Can the issue be due to temp profile of the chip being not observed?

    Is there a chance for wrong part batch?

    What do you think.

    Certainly voltage order will not be involved as the two I have on my desk are fine.

    What do you think?

  • Sebastian,

    This is hard to say.  In order to find the root cause you would need to do a swap of devices.  Unless your thermal profile is so much different than normal I would not think that would be an issue.  Not saying the device is bad but in my experience I have seen more error in the build of the PCB board or the assembly process that causes a leakage path.  I would attempt to clean the boards that failed.  That is the easiest and quickest way to determine if it is flux on the board.  Depending on the solder used I think the preferred cleaning is differ net.  Next I would replace or reinstall the devices.  Checking the voltage drop without the INA210 installed could tell you if something on the board leaking.

  • Hello Javier,

    I have cleaned the board - no improvements.

    I agree with you that the next stage is to repalce the IC. This is quite difficult at the moment and knowing that 2 out of 4 boards work fine and I have an option to isolate ina210 I will have to accept it.

    Thank you very much for your help , the measurements and the comitment , the results you provided  me with are very helpful and reassure me that the circuit is correct and fault is in assembly process.

    Thank you very much

    Sebastian

  • Hi Sebastian,

    I still think that the INA210 got damaged by ESD or EOS. I would add TVS to the inputs as discussed in section 7.4.4 of datasheet.

    Kai

  • Yes, after all I do not know what caused these parts to fail, so adding ESD protection is on my list and I willconsider using it in new versions of this circuit.

    Thanks

    Sebastian

  • Good luck :-)

    Kai