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Op-Amp Selection

Chris Rhodin
Prodigy 40 points
Other Parts Discussed in Thread: LM3S617, OPA365

I need an op-amp suitable for current sensing on a switch-mode H-bridge stepper motor driver.  I plan to place a current sensing resistor in each of the ground legs and feed the signals into a simple differential amplifier.  The output from this amplifier will feed into the ADC on a Stellaris LM3S617.  The question is, Which of the 600+ available op-amps is right for this application?  My criteria is pretty broad; single supply, fast enough to recover from the switching glitches, high CMRR, enough precision for a 10-bit ADC.  Right now I'm leaning toward the OPA365 but don't know if I've missed something.

Thanks,

 

Chris Rhodin

 

  • 0
    Genius 5430 points

    Chris;

    Trying to build your own differential amplifier with an op amp and a handful of 1% resistors is a recipe for disaster. To get decent common-mode rejection in a diff amp, you will need resistors with at least 0.01% accuracy and matching temperature coefficients. Buy one from TI or ADI, etc-- those internal laser-trimmed resistors are far more accurate than you will find in a parts bin-- actually, an IC diff amp will be cheaper than what the accurate parts will cost you.

    Regards, Neil P. Albaugh   ex-Burr-Brown