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MC33926 help needed, pinouts and DC supply questions


#1

I am having some difficulties understanding the MC33926 motor driver connections.

I’ll start with power. I am supplying Vin and Gnd from the large screw terminals. This is a 12v plug pack style 240v to 12v isolated (probably switchmode) powersupply. Beside the MC33926 is a Teensy that, in my prototype, is powered from USB and has its own 5vDC regulator.

If I supply Vdd on the MC33926 with a logical 5vDC from the MCU what happens with GND ? Does it matter that the GND for the MC33926 is supplied by the switchmode 12vDC supply ?

Next is the MC33926 control pinouts. If I hold IN1 HIGH and IN2 LOW I will get motor direction one way. Now from reading the data sheet for the MC33926 it seems I can hold the INV pin to change direction. Is this correct ? If so then I can control direction with one MCU pin and PWM with another MCU pin connected to D2.

What do I do with D1 ? Do I leave it in its default HIGH state or do I pull it LOW ? I don’t really understand the ‘tri-state’ logic.

The Pololu page says I can also supply PWM to IN1 or IN2 if both disable lines are ‘inactive’. How do I make D1/D2 inactive ?

Any help would be appreciated.


#2

Hello.

I am sorry you are having a difficult time using the MC33926; we understand the MC33926 has a complex control interface and try to make it easier to use by listing each pins’ function and default state as well as providing basic connection suggestions on their product pages. It sounds like you might be using the MC33926 Motor Driver Carrier.

In general, there should be a common ground shared between all components in your system, so you should connect GND from your Teensy board to the MC33926.

You might find looking at the pinout table under the “Pinout” heading on the MC33926’s product page (if you have not done so already) helpful in understanding the function of each pin on the board. Like it says in the table, INV can be used to invert the motor direction if IN1 and IN2 are set to different values.

D1 and !D2, are both active by default, so you need to pull them to their inactive states to enable the motor channel. Their default (or active) states are also defined in the pinout table.

Tri-state logic, also known as a three-state logic, uses a third state, high-impedance (floating/disconnected) state, in addition to logic high (1) and low (0). When a motor driver output is at high-impedance, the motor is coasting. You can find more information about the different output operations in the truth table on page 17 of the MC33926’s datasheet.

- Amanda


#3

Thanks for the reply. I got it all working. Now just having issues getting the DC train motors turning at anything less than 75% duty cycle.

I am trying to understand s-curve maths in an attempt to create a lookup table to implement a non-linear PWM output.