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Use of ADuM4190 as current feedback on DC brush-type motor controller

Question asked by eoverton on Jan 13, 2017
Latest reply on Feb 8, 2017 by eoverton

Is there a good app note for using the ADuM4190 as a current shunt amplifier on the ground leg of a brush-type DC motor controller?  Specifically I'm looking to limit bandwidth (via the compensation pin, perhaps) to be able to interrupt a speed-controlling PWM pulse train to the motor when it's stalled and I need to current-limit it -- or detect the stall so the motor can back away from the obstruction.

The plan is to use a comparator (with some hysteresis) further downstream from the ADuM4190 to decide if this is the place to shut off the signals to the gates of the FET's on the motor's H-bridge circuit.  When current drops, the PWM train gets resumed.  It's a crude way to implement current limiting, I know.  But for a mechanical system, it's probably good enough.

 

Inrush currents on the motors we have to support can be quite high (tens of amperes), but steady state currents under load generally run to about 250mA to 0.5A.  Stall currents are typically in the 1A - 4A range.  Among the concerns is getting a current sense shunt resistor with a value high enough that the ADuM4190 has a decent signal to work with but low enough that it can be put in a physically small package and where on current inrush the bottom of the motor (the "-" lead) doesn't float up to where V(gs) of the n-channel FET that routes current to ground doesn't shrink to where the FET turns back off.

 

Any thoughts?

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