INA146: Vin+ Internal Resistor Tolerance

Hi David,

We don't provide minimum and maximum values for the INA146 internal resistors because their initial values are as processed values and their final values aren't especially important to the overall operation of the amplifier.

The resistors, R1 through R4, are laser trimmed at wafer probe to achieve maximum common-mode rejection (CMRR) and to minimize gain error (Ge). Therefore, what is critical are the resistor ratio matchings and not the actual resistor values. As an estimate the final value of the resistors is likely within +/-15 % of the typical value, but no assurances are provided that will be the case because the resistances are specified as "typical."

R5 is trimmed for a 10 kilohm value with 1 % tolerance and it is the one exception. That is done so that the as the datasheet explains "This provides bias current cancellation (in combination with internal R5) to assure specified offset voltage performance."

Once the resistors are trimmed for maximized CMRR and minimized Ge performances what then becomes important is not to throw things off by driving Vin- and Vin+ with unbalanced source resistances. It only takes fractions of an Ohm in one path or the other to severely degrade the amplifier's high performances.

Regards, Thomas

Precision Amplifiers Applications Engineering