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INA826EVM: Output saturation

Marvn Arcangel
Genius 10645 points
Part Number: INA826EVM
Other Parts Discussed in Thread: INA826

Hi Team,

Can you help with the inquiry below?

"Previously, the evaluation board was working fine. The evaluation board is working on a dual supply. However, the V- pin was a little loosened, but I reconnected it to the board while the power was on (-15V). I checked all the connections and found out that there is no short connection. It's only that while reconnecting the V- terminal there was a bit of sparkle as the power supply was connected.

Here attached are the input and output of the board. Input is the sine and output is the saturated voltage. I am facing the same issue for 2/3 boards as there is a sudden misplacement and I tried connecting it while the power supply is on. "

Can you help diagnose the issue?

Thank you.

Regards,

Marvin

  • 0
    TI__Guru 57061 points

    Hi Marvin,

    Marvn Arcangel said:
    "Previously, the evaluation board was working fine. The evaluation board is working on a dual supply.

    What is the gain resistor settings at Rg? If Rg is open or no resistor is connected, then Gain = 1 V/V, your output should be follow the input with dual supply rails.

    Are you saying that the EVM is no longer working even you repeat the previous configuration? Please repeat the previous settings and let me know what the circuit is doing. 

    Marvn Arcangel said:
    Can you help diagnose the issue?

    I need more details about your setup. Based on the scope shot, it looks like that you are input 1Vpp @10kHz (blue trace). The green trace is measured approx -14Vdc. What is the green trace? On the upper right corner between a and b measured nodes, delta voltage is 19.90Vdc. Where is the measurement?

    You mentioned that there are 3 boards. Can you compare the voltage nodes between the working one vs.  non-working unit?

    Please feed me more measurement information and I will try to figure out what is going on. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    TI__Genius 10645 points

    Hi Raymond.

    Here is additonal information:

    Raymond Zhang1 said:
    What is the gain resistor settings at Rg? If Rg is open or no resistor is connected, then Gain = 1 V/V, your output should be follow the input with dual supply rails.

    The gain is 1 and there is no resistor for the RG. (Please ignore the value at the right upper corner.) Please see connection below:

    +15V to V+ from power supply 
    -15V to V- from power supply
    Ref is connected to GND
    No resistor for the RG 
    Raymond Zhang1 said:
    I need more details about your setup. Based on the scope shot, it looks like that you are input 1Vpp @10kHz (blue trace). The green trace is measured approx -14Vdc. What is the green trace? On the upper right corner between a and b measured nodes, delta voltage is 19.90Vdc. Where is the measurement?

    The output voltage(green curve) does not show any sinusoidal waveform. The input blue curve is sinusoidal waveform. The green curve is the output voltage from EVM (VO node). When the board was working, they got 1Vp-p sinusoidal waveform from Vo node. Now it is showing -14V. 
    The customer saw sparks when they reconnected the V- terminal while the power supply was on. It appears that the third board is also damaged due to the same action they made. Is there any solution to this? is replacing the  INA826 itself can solve the issue (or some busted Cap/Res)? or is it more logical to purchase a new EVM
    Thank you.
    Regards,
    Marvin
  • 0 in reply to Marvn Arcangel
    TI__Guru 57061 points

    Hi Marvin,

    Marvn Arcangel said:
    The customer saw sparks when they reconnected the V- terminal while the power supply was on

    Based on your description, I have a feeling that the INA826 is damaged somehow. You may measure the resistance between Vo to -V rail and see there is a short or low resistance. Please current limit the power supply rails to ±100mA or so at ±15Vdc, when you are trying to do the test on a bench. 

    I would replace the potential bad INA826 EVM with a fresh instrumentation amplifier. It is not difficult to replace the SOIC-8 package. All you need is a hot air gun and solder iron. If you do not have hot air gun, you may try to cut SOIC-8's leads (with care), clean the pad with a solder wick and resolder a new part on the INA826's pad.  Alternatively, you may get another INA826 EVM. 

    Enclosed is a sample of simulation. If the differential input is 2Vpp or similar, the output of Vout will follow the input with Gain = 1 V/V at 10kHz. 

    INA826 Gain-1 10312022.TSC

    If you have additional questions, please let me know. 

    Best,

    Raymond

  • +1 in reply to Raymond Zhang1
    TI__Guru 57061 points

    Hi Marvin, 

    I hope that your issues are resolved. 

    I am going to close this inquiry. If you have additional questions, please let us know. 

    Best, 

    Raymond