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INA600: Close but no cigar.

Ian Benton
Prodigy 230 points
Part Number: INA600
Other Parts Discussed in Thread: INA187, INA181

Just spotted the INA600 with a gain of 1/24. How perfectly ideal for getting the cell voltage of a floating 24-cell battery to my processor's A/D. But wait! Maximum negative common mode voltage (or is that maximum negative input voltage) is -40V. A 24V cell battery can be charging at 58.8V, and what happens if B+ gets shorted to ground?  So what could I measure with the INA600 and its 1/24 gain?

  • 0
    TI__Mastermind 33271 points

    Hello Ian!

    Thanks for posting on E2E! Just wanted to make sure I am understanding the scenario you are describing. In an overvoltage condition, current into IN+ and IN- would have to be limited to less than 10mA. Additionally you can add some external protection components to protect the INA600 from miswiring damage. I can help give some suggestions, but would probably need a little bit more information. Do you have an equivalent schematic of the scenario you are describing? 

    Best,
    Gerasimos

  • 0 in reply to Gerasimos Madalvanos
    Prodigy 230 points

    I have a 48V Lead-acid battery, which is "floating" (not completely isolated) and my control circuitry is grounded.

    To be honest I came across the INA600  by accident looking for something like an INA181 that could stand more negative voltage (found the INA187), but I found the INA600, and thought "fantastic divide by 24 - perfect for measuring the voltage of a floating 24-cell battery", and then I thought "but what happens if the floating battery floats to the positive supply, not quite so perfect any more because it has exceeded the input voltage range. 

  • 0 in reply to Ian Benton
    TI__Mastermind 33271 points

    Ian,

    Understood, if the battery is floating in relation to the INA supply rails, that is where the key limitation is for absolute maximum rating. It sounds like your best bet would be to use an isolated amplifier, unless I have misunderstood your system. Where the INA600 fits best is for monitoring voltage rails on a similar reference, or at least one that is not floating relative to the INA supply rails. This is a little different in architecture than the INA181/187 which are shunt references, and in the INA187's case it is powered off of the input voltage.

    The INA600 is an attenuating difference amplifier, and works similarly to a discrete difference amplifier you would build with a few well-matched resistors and your favorite op amp of choice. The main differentiators here are that we internally compensate the common-mode voltage range to remove the need for some of the VCM range math, integrated the resistors on die to give excellent relative matching/drift performance, and the input ESD structure allows for powered inputs while the device is unpowered. 

    Best,
    Gerasimos