I looked around on here, and used google, and couldn't find a direct answer to this question. Please forgive me if I overlooked something.

I am working on a board to control a BLDC motor (BLWS231D-24V-2000) which has a set of integrated Hall effect sensors that I will be using in conjunction with an external capacitive encoder (AMT102-V). I will be powering the sensor with +5V coming from the Driver IC (TI DRV8323SR) I am using. Through conversations with an application engineer at the motor manufacturer, I learned that when the Hall effect sensors (open collector output) are floating, I "should" read about 6.3 V, if I were to hook them up to a scope. The MCU (XMEGA128A4U) I am planning to use operates on 3.3 V logic. Before learning about the approximate voltage from the Hall sensors in their floating state, I was planning on using a pull-up resistor to the 3.3 V supply line that will be coming from a separate linear regulator to drive the floating voltage to the logic voltage for my chip.

Planned pull-up scheme

My question:

Should I set up a resistor divider circuit so that the floating voltage from my Hall sensors is forced to be at or near 3.3 V, or will using the pull-up scheme shown above work? Or should I be looking for a different solution to the voltage issue all together? Or is there an issue? I don't want to damage any pins on my MCU and have to completely re-design the board. This is my first experiment with hall sensors for motor control.


1 Answer 1


The spec says...

4.5V min for Hall sensor so you can use 5V and open collector may pull-up to your 3.3V. I don’t understand open collector and 6.3V floating. Unless that is simply stray leakage voltage from 24V Motor supply with 10M probe. Using 3.3mA to 3.3V with 1K will absorb any stray leakage and possibly 10K as well.

  • 1
    \$\begingroup\$ Thanks for the feedback! I was going to query the person I spoke with further regarding the voltage question, but I was on a break from work and ran out of time. The 6.3V reading didn't make sense to me either, so I'm glad I'm not the only person who thought that sounded odd. Without knowing how they did their testing I can only speculate, but your idea re: a 10M probe makes sense to me. Thanks again. \$\endgroup\$
    – Nate
    Oct 11, 2018 at 4:03
  • \$\begingroup\$ You’re welcome , I wish more experts would agree as well. (But they are shy ) \$\endgroup\$ Oct 11, 2018 at 17:38
  • \$\begingroup\$ These Hall sensors are open drain outputs, any voltage seen on the outputs on the off state is just from leakage. Your supply/pull-up scheme is the standard arrangement for a 3.3V controller. \$\endgroup\$
    – Phil G
    Oct 11, 2018 at 19:04
  • \$\begingroup\$ Thanks @PhilG. How did you determine that they were OD rather than OC? From experience, or am I misreading the spec sheet? The sheet indicates OC, is it incorrect? (This is why God made EEs to go with MEs. Which came first is a matter best left to scholars, I suspect). \$\endgroup\$
    – Nate
    Oct 12, 2018 at 2:39
  • \$\begingroup\$ I think @PhilG may have it wrong. Some motors may have open drain for analog amplification, but not these ones. There is only an open collector note, so 4.7k ought to work with a wide tolerance. \$\endgroup\$ Oct 12, 2018 at 6:21

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