I'm currently using a demo-board from sparkfun for quick prototyping of a hall-effect sensor application. The specific chip I'm using is the ACS723-5AB, a Hall-Effect sensor that can measure between -5A and +5A.

Now that I'm done using the demo-board from sparkfun I'm looking to just directly use the sensor chip in my final circuit design.

One of the improvements I wanted to make was to add a low-pass filter on the sensor output for smoothing the signal a bit by adding a simple RC filter, but when I look at the circuit-design of the SparkFun board, they don't use an RC filter but just a capacitor to ground on the output line.

I can't imagine anything drawing current from the sensor output, so decoupling doesn't seem likely. It doesn't really create a filter without a resistor (as far as I know?)

My question is: What is the purpose of capacitor C2 on Viout?

enter image description here link to circuit diagram of daughterboard

Link to sensor datasheet


1 Answer 1


It doesn't really create a filter without a resistor (as far as I know?)

It probably does because it's likely that the output amplifier will have some output resistance that isn't trivially small. The data sheet tell us two things here: -

  • Output Resistive Load from VIOUT to GND is 4.7 kΩ minimum
  • Output Capacitance Load from VIOUT to GND is 10 nF maximum

This fairly convinces me that the output impedance is not insignificant else why have such a high minimum load AND why have such a high limit for output capacitance; most op-amps would probably go unstable with a load capacitance as high as 10 nF so, I expect that there is an internal output resistor.

What is the purpose of capacitor C2 on Viout?

An extra means of reducing high frequency output noise.

  • \$\begingroup\$ Thanks for the answer! So if I understand correctly there is an internal resistor and by adding just a cap to the output you basically create an RC filter? If so, what kind of output-cap value range should I be thinking of? (sorry for the probably basic question, quite new to analog electronics) \$\endgroup\$ Jan 9, 2020 at 11:38
  • 1
    \$\begingroup\$ The maximum allowable is 10 nF (according to the data sheet). Unfortunately the DS gives no clue as to what sort of pass band this will give. \$\endgroup\$
    – Andy aka
    Jan 9, 2020 at 11:39
  • \$\begingroup\$ Alright, again, thanks a lot for your time and answer :) \$\endgroup\$ Jan 9, 2020 at 11:40

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