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INA129-HT: REF pin Input range

Marvn Arcangel
Genius 16830 points

Part Number: INA129-HT

Hi Experts,

I couldn't find one information in datasheet related to the valid input range of the REF Pin in INA129-HT. Please help to understand the valid input range to this pin.

Thanks!

Marvin

  • 0
    TI__Mastermind 31400 points

    Hi Marvin,

    Thank you for pointing this out. I hadn't noticed that it was not included in the datasheet. They definitely focused on REF = 0V applications. 

    Do you know what the customer's needs are? Such as: 

    • Desired output voltage range? 
    • Supply voltages?
    • Input common mode range? 
    • Gain? 

    The more information provided the better I can help determine a valid reference voltage. 

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    TI__Genius 16830 points

    Hi Robert,

    The project involves replacing an existing HTOP01 op-amp with an OPA2333HT or INA129HT to interface with a Kulite sensor at a gain of 29. A key requirement is adding a 1–50mV offset adjustment for temperature calibration while keeping the hardware changes minimal and the firmware identical.

    Regards,

    Marvin

  • 0 in reply to Marvn Arcangel
    TI__Mastermind 31400 points

    Hi Marvin,

    Thanks for the background. 

    I could verify the input range of the REF pin by tying the inputs to mid-supply and then applying a sinusoidal signal to the REF pin. I don't have any devices on me, so I'll need to order some to make the tests. Might take a while to get here. 

    Those two have very different pinouts. It would look like a board spin would be needed if you went with either device. 

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    TI__Genius 16830 points

    Hi Robert,

    Thank you for checking. I will wait for the result of your test.

    Regards,

    Marvin

  • 0 in reply to Marvn Arcangel
    TI__Mastermind 31400 points

    Hi Marvin,

    I have ordered the parts. I'm hoping to get them early next week, but I'll keep you in the loop as things progress! 

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    TI__Genius 16830 points

    Hi Robert,

    Thank you. But for now, could you please confirm if the pin is capable of sensing from 0.00V to 100mV?

    Regard,

    Marvin

  • 0 in reply to Marvn Arcangel
    TI__Mastermind 31400 points

    Hi Marvin,

    Could you share with me:

    • What are your supply voltages?
    • What are your input voltages?
    • What gain are you in?

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    TI__Genius 16830 points

    Hi Robert,

    As shown in the previously attached screenshot, the supply voltage is 4V5, the gain is 29, VCM is to be 2.25V( ideally) and max deviation is 100mV.

    Thanks!

    Marvin

  • 0 in reply to Marvn Arcangel
    TI__Mastermind 31400 points

    Hi Marvin,

    I'm so sorry for asking what you had already provided. 

    I still can't do anything till I get some devices in to test. 

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    TI__Mastermind 31400 points

    Hi Marvin,

    The parts came in and I got to testing as quickly as I could. 

    What I did was I put +/-10V supplies, grounded the inputs and put a sine wave on the reference pin that was centered at zero. When I did that I saw that the device's reference voltage can get about 0.7V from the supply rails before any clipping was present on the output. 

    Let me know if there's anything else you need! 

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    TI__Genius 16830 points

    Hi Robert,

    Thank you.

    Regarding the minimum voltage to the ref pin, does the pin support 0.00V to 0.1V (0-100mV input range)? The customer would be injecting the reference/correction voltage in the range of 0-50mV range.

    Could you please specify the Voltage input Range to this pins? Whether it is rail to rail input? or minimum 0.7V needed to operate?

    Thanks!

    Marvin

  • 0 in reply to Marvn Arcangel
    TI__Mastermind 31400 points

    Hi Marvin, 

    Marvn Arcangel said:
    Could you please specify the Voltage input Range to this pins? Whether it is rail to rail input? or minimum 0.7V needed to operate?

    Of course! Also I realized that I made a mistake. The range isn't symmetrical. It's actually (V-) + 0.1 <=VREF<= (V+) - 0.7V. 

    Marvn Arcangel said:
    Regarding the minimum voltage to the ref pin, does the pin support 0.00V to 0.1V (0-100mV input range)? The customer would be injecting the reference/correction voltage in the range of 0-50mV range.

    Let's take a look at the customer's schematic, where the supplies are 0V and 4.5V. That would mean that the input range for the reference pin is 0.1V <=VREF<= 3.8V. This shows that the ref pin doesn't support 0-0.1V range with the current supplies. I'd recommend adjusting the supplies to support a lower reference voltage or changing the reference voltage that's being injected in it. 

    Best Regards,

    Robert Clifton