ATtiny 26 and Freescale MC3887

[sballs]

Hello,
I am using an ATtiny26 to control a Freescale MC33887 H-bridge with current feedback. The data sheet for the h-bridge states that the current feedback is 1/375 of the measured load current, and the resistance range for the linear operation of the FB terminal is 100 < RFB < 200 ?.

My motor has a maximum current draw of 500mA and I am using a feedback resistor of 200? => The maximum voltage to the ADC will be (500mA/375)*200 = 266mV. I would like to shut the motor off at 350mA or 186mV.

What is the best way to go about measuring this accurately? Should I use a differential input with 20x gain (ADC2 to FB signal and ADC1 to GND)?

Do I need to add filtering to the ADC?

Thank you!

 

[itsmoked]

I'd just go with a non inverting single ended amp. (After) I made sure that the 266mV range was too small for the ATtiny.

And yes you want to use some RC filtering on the Freescale side, since there could be some current noise translated to FB voltage noise. Noise will drive you cazy on a closed loop.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com