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).
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.