I am using the Hall-effect sensor OPTEK 3075S to ensure every step commanded to a stepper motor is executed. In the datasheet, they recommend connecting a 100nF capacitor across he input pins for "stable operation". I have been successfully using this sensor without cap with short supply wires for months, and now that I am planning on using this sensor after a few tens of meters I wonder if this is required.
I know it is easy enough to add the cap anyway (although I would need to build another PCB), but I do not like to add components without understanding their added value:
- how would the current source of the Hall element (which apparently is a voltage regulator across a constant resistance) be less stable without cap, given that there is nearly no load, and that the power supply rejection is not so important (since this is a digital sensor)?
- Certainly the opamp is the one which may become unstable? Is it possible that stability would only result in unstable transients but the output would not be affected after the step has been made?
- Is there a way to quantify/estimate the gain in stability margins by adding the cap in (with respect to what? Supply variations? Hall element output?)?
Note: the sensor state transitions are located dead-on between two steps (45° per step) for stable output for every motor positions, and the motor step rate is 5 steps per second.