• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 48 subscribers
  • Views 169 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

INA592: The output voltage isn't the voltage I want

zhongfei zhao
Prodigy 111 points
Part Number: INA592


Tool/software:

I built the following circuit using INA592. The voltage measured across R164 doesn't match my expected value. Theoretically it should be (V / R147) * R164. Where could the issue lie?

Additionally, I measured the voltage on the left side of R147 with a DMM: 4.85788V, and the right side: 1.7493V. But when I directly measured the voltage across R147 terminals, it was 2.99992V. This value doesn't match the result obtained by subtracting the individual measurements. What could be causing this discrepancy?

  • 0
    TI__Mastermind 33583 points

    Hello Zhongfei,

    In this configuration, the transfer function will be the following:

    Vout = (Vref-Vsense)*2 + Vin+

    Vin+ is going to be Vout*(620.5k/1.6235MEG) (voltage divider formula) This term simplifies to 0.38219

    This now gives us the transfer function of

    Vout = (Vref-Vsense)*2 + Vout*(0.38219)

    Rearranging to get everything in terms of Vout

    Vout - Vout*(0.38219) = (Vref-Vsense)*2

    Vout(1-0.38219) = (Vref-Vsense)*2

    Vout = (Vref-Vsense)*2/(0.617801)

    or

    Vout = (Vref-Vsense)*3.237288

    In this case, your output voltage is going to be (1.49996-0)*3.237288 or 4.8558027

    From the measurements you provided, if there is a 1.7495V potential on the right side of R147 and a 2.99992V drop across R147, your output voltage is 4.74942

    Is the difference you are seeing this 100mV between ideal and measured?

    Best,
    Gerasimos

  • 0 in reply to Gerasimos Madalvanos
    TI__Mastermind 33583 points

    Zhongfei,

    Additionally, I see that C156 is marked as NC, but this component is not recommended for amplifiers. The following article describes the negative impact of a capacitor between inputs on discrete difference amplifiers but is applicable to other amplifier applications as well.

    https://www.planetanalog.com/a-closer-look-at-discrete-difference-amplifier-implementation/

    Best,
    Gerasimos

  • 0 in reply to Gerasimos Madalvanos
    Prodigy 111 points

    Yes, I want to understand how this 100mV difference arises. It seems that 2.991uA of current flows through R147, and all this current passes through R164. Therefore, the voltage generated across R164 should be 2.991uA * 620.5K = 1.856V. However, the measured voltage of R164 is over 100mV lower than this.

  • 0 in reply to zhongfei zhao
    TI__Genius 16400 points

    Hi Zhongfei, 

    When you are measuring the load output voltage, are you measuring the voltage across R164? Also, can you confirm what the output of U24 is? 

    Regards,
    Ashley