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INA149 + External ADC - individual cell voltage monitoring in stacked voltage system

William W
Prodigy 20 points
Other Parts Discussed in Thread: INA149, LMP92064, INA220, AMC1200

Dear friends,

I want to use INA149 with external ADC for measuring individual voltage cell in stacked voltage system.

The maximum voltage of the system is 800V.

Can I use isolated modules of INA149 as shown below?

What supplies should I use to power the difference amplifiers?

Any better solution?

Thanks,

William

  • 0
    TI__Guru* 92715 points
    William,


    I'm going to split this off into its own post. Since it really addresses an amplifier question, I'll move it over to the Precision Amplifier Forum.


    Joseph Wu


    I'll note that the original post from which this was split off came from here:

    e2e.ti.com/.../197128
  • 0
    TI__Mastermind 25775 points
    Hello William,

    The common-mode voltage range of the INA149 is +/-275V given +/-15V supplies. The typical relationship between supply voltage and common-mode voltage is given by Figure 3 in the INA149 data sheet. As you will see, even with a single 36V supply the common-mode voltage does not extend to 800V, therefore you will need isolation. Depending on the voltage of each cell, you likely won't need isolation for Module #1 (and perhaps a few more of the Modules at the bottom of the stack). However, as the common-mode voltage (or bus voltage) increases you will need to derive the INA supply voltages (and ADC) from the bus voltage and the isolate on the digital side. The idea is shown by Figure 23 in the LMP92064 data sheet and Figure 23 in the INA220 data sheet.
  • 0 in reply to Pete%20Semig
    Prodigy 20 points

    Hi Pete,

    Thank you for your reply.
    I have a new problem in my design. There are 33KOhm resistors in series with each cell test point as shown below, and I think I will lose accuracy in cell voltage
    measurement.


    The voltage of each cell is between 0-5V, and the current that can be sunk from each cell is limited to 100uA.
    Can I use isolation amplifier instead of INA149?
    Which isolation amplifier would you recommend me to use?  (e.g. AD202, ISO103)
    Do you have any better solution?

    Regards,
    William

  • 0 in reply to William W
    TI__Mastermind 25775 points
    Hello William,

    Yes, you will definitely introduce error by placing external resistors in series with the inputs of a differential amplifier. That is because the resistors inside a difference amplifier are laser trimmed for accuracy and drift. The error due to external resistors (both accuracy and drift) will be greater than that of the internal resistors.

    The AD202 is not a Texas Instruments device. While the ISO103 is a TI device, it is not recommended for new designs (NRND).

    Correct me if I'm wrong, but I believe you can't (or don't want to) power the INA and ADC with the common-mode mode voltage.

    Therefore, the only other device that I can think of is the AMC1200. However, it has a fixed gain (8V/V) and therefore fixed input voltage range (+/-250mV). Perhaps you could place shunt resistors in series with the batteries (though this will of course dissipate power). If you have further questions about the AMC1200, please note that it is supported via the Precision Data Converters forum.

    I hope this helps!