I am making a BLDC motor controller , so can you tell me the use of pullup resistor connected in the feedback of hall sensor.And is HO is equal to VB voltage when driver circuit operates ? Please explain the value of phase output voltage coming ( Explain any phase voltage).enter image description here

  • 2
    \$\begingroup\$ How can we read the datasheet to tell you the pull-up value if you don't tell us which part it is? \$\endgroup\$
    – Justme
    Oct 28, 2020 at 16:40
  • \$\begingroup\$ I only want to know the use of this pullup resistor \$\endgroup\$ Oct 28, 2020 at 16:51
  • 6
    \$\begingroup\$ Maybe the outputs are open collector? Hard to say without a datasheet! \$\endgroup\$
    – Aaron
    Oct 28, 2020 at 17:05

1 Answer 1


Circuits with pullups generally pull down the voltage sharply to ground then let go, relying on the pullup resistor R to pull the voltage high. How quickly it can pull the voltage up is a function of R and any capacitance on the line.

If the sensor signal is changing so quickly that the pullup doesn’t have time to pull the voltage up between transitions then you have a problem. This limits the upper bound of R.

The lower bound of R is dictated by how much current the sensor driver can sink, which is a function of its output impedance.

Lacking any specifications of your sensor device, R=1K is a good place to start.

  • \$\begingroup\$ Lower limit of R is also dependent on the supply current available for it. \$\endgroup\$
    – TonyM
    Oct 29, 2020 at 5:56

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