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I'm working on a small project of mine and I need to implement a motor driver in order to control a 3 phase Brushless DC motor.

By googling, I've read that I need a High and Low side driver to control the couple of NMOS used the generate on of the phases.

Can I just connect the pins of my μC directly to the MOSFETs and just enable and disable it via software?

Could you explain me why do I need such a piece of hardware?

I've seen the L6234 Three phase motor driver from ST, and they use some logic ports to manage the enable/disable of the inputs.

Thank you in advance!

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  • \$\begingroup\$ DIY three-phase BLDC motor control is not a trivial task. Some resources to look at would be TI's InstaSPIN and InstaSPIN-FOC, which works for sizable motors. If you are small size/high speed, check the drone community's open-source hardware and software for SimonK-based controllers. Allegro makes chips tailored for BLDC control - their datasheets may help explain a lot. \$\endgroup\$
    – Smith
    Jun 27, 2016 at 22:06

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Couple of things. Your "brushless DC" motor is an AC induction motor and your three phase motor driver is what makes it appears as a DC motor to the outside world.

You need high and low side drivers to produce some sort of AC to the motor windings and especially to create a voltage difference between two adjacent windings.

Hypothetically, you might be able to pull off some kind of push-pull scheme with only low side transistors but since you can't interface your logic ports to the MOSFETs in the motor driver part of the motor driver, you are going to need gate drivers anyway and they in turn can be interfaced to normal 3.3 V logic (I assume 3.3 V on your behalf).

IR2113 is a good start. Datasheet here: IR2113. Or the L6234 if it's low voltage and you want everything integrated.

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  • \$\begingroup\$ Thank you for your answer! What do you think if I use these components in order to build the motor driver on my own: L6743D - High current MOSFET driver and STS4DNF60L - N-channel 60 V, SO-8 STripFET™ Power MOSFET? Could they make it? \$\endgroup\$
    – starScream
    Jun 27, 2016 at 15:41
  • \$\begingroup\$ You are welcome! What are your requirements. What is the DC bus voltage? How much power? \$\endgroup\$
    – winny
    Jun 28, 2016 at 7:14
  • \$\begingroup\$ I am using what I have in the lab, hence the requirements are a maximum current of 4 A and a maximum DC voltage of 20 V for the power MOSFTETs and reduced to 12 V for the drivers. I saw that there's an example of connection in the Application circuit section page 3, but I really don't know how to choose the passive elements (Resistances, Capacities etc) in order to connect the two chips. \$\endgroup\$
    – starScream
    Jun 28, 2016 at 9:54
  • \$\begingroup\$ If your knowledge is limited to choose the passives, you are better off with a fully integrated driver like the L6234 you suggested but as Brian pointed out, you are limited to useing the same drive voltage as logic voltage. Are you using 3.3 V logic levels? \$\endgroup\$
    – winny
    Jun 28, 2016 at 10:14
  • \$\begingroup\$ I haven't decided yet, I am fine with both of them \$\endgroup\$
    – starScream
    Jun 28, 2016 at 10:28
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The L6234 provides those high and low side drivers internally, they are the amplifiers (triangular blocks) running down the centre of the block diagram.

You will notice that the high side drivers have their own power supply (VBOOT) which is higher than the main supply, generated by a charge pump.

This arrangement allows both high and low side MOSFETs to be NMOS, which (for a given transistor size and cost) have a lover ON resistance and therefore switch more efficiently than PMOS transistors. (You can see them on the RHS of the block diagram).

You CAN make a BLDC motor controller without high and low side drivers - BUT
(a) the high side transistors must be PMOS, which are OFF when their input is VDD, and ON when it is 0V.
(b) the motor and the CPU must share the same VDD (probably 5V) so that the CPU output levels are the right voltage to turn both transistors on and off satisfactorily. This low voltage only allows relatively low power motors.

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