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INA333-HT: Stability at 210 degC

Brandon Dyer1
Intellectual 500 points
Part Number: INA333-HT
Other Parts Discussed in Thread: INA129-HT, OPA2333-HT, INA128-HT

Hello,

I have a question concerning the stability of the INA333-HT at 210 degC.  The data states that if this device is going to be operated at 210 degC there must be an RC series network added at pin 1 and at pin 8 (the negative terminals of the input stage amplifiers) with both referenced to ground.  The recommended values are a 10nF capacitor and a 3.5kohm resistor.  I am limited to resistor values of 1k, 4.99k, and 10k  and capacitor values of 10nF and 33nF due to temperature ratings and package requirements.  This will be a rework to my current build to add these networks; so space is critical.  Options I am considering are:

  1. 10nF and 4.99kohm:  most desirable option if it will work
  2. 33nF and 1kohm:  possible if  the 33nF is not too large 
  3. 10nF and 3.33kohm (10k//4.99k): would like to avoid stacking resistors

How much tolerance is allowed in the RC network?  Also, can you take a look at the picture below to make sure I understand the placement of these networks:

Finally, my ideal gain is ~84V/V.  Will I need to increase this gain in addition to the RC networks for the INA to be stable at higher temperatures?  Also, is it possible for instability to cause the INA to have what looks like unity gain when the RC networks mentioned above are not connected and G=84V/V (given that all other requirements are met, such as DC return path is provided on inputs, common mode input range is not violated, Vref is from a low impedance source, etc.)?

Thank you,

Brandon

  • +1
    TI__Genius 10850 points

    Hi Brandon,

    Thanks for your post, I can help you.

    Page 14 of the datasheet mentions the following:

    "It is not recommended to use a gain < 100 for high temperature (210°C) applications. For gains > 100 in such applications, a compensation circuit is needed at pins 1 and 8. The circuit is needed at each pin and consists of a resistor in series with a capacitor referenced to ground. Recommended values for the resistor and capacitor are 3.5 kΩ and 10 nF respectively."

    The added passives provide stability/compensation to permit the use of high gains at high temperatures, but there is no guarantee the compensation will work under your specified low-gain conditions. If possible, I would recommend you increase your gain to above 100V/V. In regards to your question about the resistor and capacitor values, the best way to verify would be to test it. This is not a spec we can simulate. You may consider selecting components whose time constant is similar to 3.5 kΩ and 10 nF.

    Lastly, you have the resistor and capacitor correctly connected in your schematic. 

    You may also want to consider exploring other part options, such as the INA128-HT, INA129-HT, or even OPA2333-HT.

    Hope that helps.