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high side current amplifiers were built in integrators?



Jan 1, 1970
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.



Jan Panteltje

Jan 1, 1970
On a sunny day (26 Apr 2007 07:46:46 -0700) it happened Michael
<[email protected]>:

I would personally see if I could get a trigger on a PIC comparator
input, say 20mV should be possible.
then use a PIC with more then one comparator and do the timing and math
in software, serial out of whatever.
Or use a PIC with AD and input mux.
One or 2 chip solution for all three motors.

I know people here have demanded that when recommending a PIC one should
also publish the asm code...
But I ain't going to do that for nopes.