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INA826: Unbalanced bipolar power supply

user5163865
Genius 3325 points
Part Number: INA826

Hi,

Our customer is evaluating INA826 at +12V / -5V power supply.
Is there a problem with this method?

I think no problem at general IN AMPs.

But, they are complaining that the power supply malfunctions when using the LTC1983-5 negative charge pump for the AD8221.

In this case, LTC1983-5 output dropped from -5V(nomal) to +0.5V.
They think AD8221 can't use unbalanced power supply.

This is a question that ADI should check, but it is an opportunity to replace it with INA826. I think that there is only INA826 because it is MSOP.
In the simple evaluation by the customer, the operation of the INA826 and the power supply IC is normal.

Is there a problem with INA826 with the following circuit and unbalanced power supply?

Because the temperature change of the forward drop voltage (VF) of the Schottky diode (RoHM / RB 060 MM - 60 TR) is unacceptable, the circuit that acquires and cancels the forward voltage with the instrumentation amplifier (G = 1)  made up.

Therefore, the anode is connected to the noninverting input terminal (+) of the instrumentation amplifier and the cathode is connected to the inverting input terminal (-).
The problem occurs at power up, so the actual VF is nearly 0V.

I'm sorry for my strange question.

Best regards,
Hiroshi

  • 0
    Guru 140200 points
    Hi Hiroshi,

    can you show us a schematic of the Schottky diode issue?

    The INA826 can easily be powered by +12V/-5V. There's no problem.

    Kai
  • 0
    TI__Guru 60570 points

    Hiroshi-san,

    There should be no problem with using INA826 with asymmetric supplies for as long as the input common-mode and the output voltage stays within its linear range as defined with respect to supplies:

    Since the valid input/output voltage ranges of instrumentation amplifiers are function of not only supplies but also gain and Vref, in order to assure linear operation please download the VCM vs Vout Calculator using link below:

  • 0 in reply to Marek Lis
    Genius 3325 points
    Hi, all

    Since I do not have a detailed circuit, I plan to visit customers.
    The unbalanced power source problem has been solved, we will close this issue once.

    Thank you for your quick response.

    I think the essential problem is as follows.
    1) Power supply sequence
    2) Charge pump output via AD8221 input ESD protection diode

    If it is correct, I believe the overvoltage protection of INA 826 is a great benefit.

    When asking again, I will post a new one.

    Best regards,
    Hiroshi