Hi there - I'm trying to monitor current going to a motor. The current going to it is in a square wave with a (fairly) constant magnitude, and a variable duty cycle. Right now I'm using a small shunt resistor combined with a high side current amplifier (Maxim MAX4372, amplifies voltage 100x) to monitor this current. But really, I mostly just have to watch for the rising and falling edges of this pulse, instead of the actual magnitude of the pulse. What would be really nice would be if I could just read in a single analog voltage that would be a sum of the current that has gone through the device since I last read it. I will be reading it at a constant frequency, about 75Hz. I was thinking that putting an op-amp integrator on the output of the high side current amplifier would make it work pretty well. Combine that with a fet on the capacitor that could discharge it after ever reading - and I think I'd have a decent setup. However - I'm really running out of space on my PCB - so three op-amps (I have three of these motors on the PCB) and three FETs would be really, really difficult to find space for. It might be doable, but I just wanted to see if anybody had any ideas for other options.
More specs about the board: motors consume about 2-400ma average. Duty cycle of current pulses ranges from about 0-100%. Everything is powered by 5V, except the motors which are 6V. An onboard microcontroller is running the show - and would be the one reading in the analog voltages with it's 10b ADC.
Any suggestions? Perhaps are there integrating high side current amplifiers? I haven't been able to find anything.
Thanks!
-Michael