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INA194 Large V-out offset

ROBERT ENGHOLM
Prodigy 10 points
Other Parts Discussed in Thread: INA194, INA210, INA213

I have five high side inductive current monitor circuits each driving hydraulic solenoids. The INA194 is used to measure the current and the inductive flyback. The specs are: 0.62 ohms sense resistor, Vs = +5V. When the high side FET driver is off the common mode voltage to the INA194 is zero. Under this condition I normally measure 0.008 volts to 0.030 volts as the offset error due to common mode voltage being lower than Vs. On the last lot of production assy's, I have measured 0.116 to 0.123 volts on specific devices. The devices in question is replaced and now in spec. If I energize the high side driver to raise the CM voltage to +12V and Vdif = 0, the offset voltage will drop by half. What is happening and any solution?

Regards, R.Engholm

  • 0
    TI__Expert 6930 points

    Hi,

    The INA194 is designed to operate accurately with input differential voltage from 20mV and higher...in your case my understanding is at times the input voltage is less than 20mV and this is where you see offset issues...and while not particularly desireable this is a known behaviour of the device and described on page 8 of the data sheet...if you are not familiar with this range of operation please have a look at the information on page 8 as I believe this applies to your situation.  If you require better offset with small input voltages (<20mV) then we will move you to another product...from what I read I see that you have a 12V common mode voltage with 5V power supply...we have several current shunt monitors that will operate over those conditions...INA210 family comes to mind...I suspect though that you mat have addiotnal requirements so please have a look at page 8 and if you cannot use the iNA194 you can post back to the forum with any additional device requirements should the INA210 family not work out for some other unforseen reason...the INA213 has the same gain as INA194...