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INA118: INA118: a question about the Gian of INA118

user5872523
Prodigy 30 points
Part Number: INA118

Hello Oliver Ou: Raymond:

This is questions from Jabil Shang Hai. Please support reply.. 

Can TI provide the allowable gain error for the gain of 5000?

How low or high the gain error of the components if the gain is set to 5000?

  • 0
    TI__Guru 61601 points

    Hi ,

    Q: Can TI provide the allowable gain error for the gain of 5000? How low or high the gain error of the components if the gain is set to 5000?
     
    Here is more gain information about INA118. 
    TI does not characterize the part with Gains >1000, though theoretically it should work with Gain =5000.  Therefore, the datasheet recommends to operate below gains <= 1000. Here are the reasons.
    1. Parasitics in Rg connection may cause significant errors
    2. With Gain=5000, the Aol of the input op amp stages start to play a role, and it can creep up the gain errors.
    3. With Gain = 5000, you may need to use max. supply voltage (+/- 18V). If the max. output voltage is set at 15Vdc, the input voltage ranges is only approx.  +/- 15V/5000 = +/- 3mV (At Vout=17.5V, the input range  has to be less than +/- 3.5mV. Therefore, you can not have more than 0.5mV variations at the INA118's input, if the input signal is close to 3mV) This means that you need to monitor the input source errors and stability of the reference pin (if Vref or pin5 pin is not connected to ground).  Slightly variations in the source errors, it will affect the INA118's output voltage greatly.  
    4. At Gain=1000, typical gain errors are approx. from 0.5% to 1%.  With Gain=5000, the gain errors will be higher.
    If you are able to control the above parameters precisely in your application, then you will likely manage the gain errors within a few percent (I do not have a number, may be < 5%) with Gains=5000. In other words, you will need to monitor above parameters carefully in your system. The sums of unwanted errors can result large variations at the INA118's output. For these reasons, we do not recommend to operate the part with gains >1000. 
    Please let me know if you have additional questions. I hope that this answered your questions. 
    Best,
    Raymond