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MC33926 disconnected IN pin

#1

Hey,
I am wondering why a disconnected IN1 or IN2 pin results in a HIGH on the OUTPUT? This is critical because when uploading a new sketch to the mcu the motor will turn full speed.

Thx

#2

Hello,

Can you tell me which specific product of ours you are using? What microcontroller are you using and how are you connecting it to the motor driver? Some pictures of your setup might be helpful.

-Dan

#3

Thanks for the reply,
I am using a MC33926 with a Teensy 3.5.
Connections:
MC33926 Teensy
GND ->GND
VDD-> 3.3V
IN2 -> PWM-pin
IN1 -> GND
D2->3.3V
D1->GND
EN ->DIO-pin
INV ->DIO-pin
So when driving the motor I use the INV to set direction. The problem is: whenever I upload a new sketch, the motor spins fullspeed for short time. I already tried a pulldown resistor on the EN line, without succes. If I unplug the microcontroller it does happen.
Looking at the truth table of the datasheet the only thing thats odd to me is that if the IN pins are floating it puts the outputs into high.

Any suggestions?
Thanks

#4

Hello,

Can you try connecting D2 to an IO pin and only toggling it high when you want the board to run?

If you still have problems, can you clarify which version of our MC33926 carrier you are using; we carry a few of them:

-Derrill

#5

Hey,
I tried using D2. So I pull down D2 with an IO and then use the D1 pin to drive pwm.
Same behaviour when uploading a new sketch.
I am using the single Motor Driver Carrier.

#6

And one additon: it doesnt happen every time, like 1 out of 3 uploads.

#7

The intermittent nature of the issue sounds like it might be due to some unreliable state the Teensy is in while programming. Can you post your sketch and pictures of your setup showing all connections?

-Derrill

#8

Hey,
I checked both IN lines with the Oszi.


Blue line is the IN line with is driven with the pwm. The yellow line is the other IN line. The moment pwm of the blue line stops is when I upload the new sketch. And depending on the last pwm state it either holds the IN line for a couple ms high or low. This explains why it happens every second or third time. So I guess it is the problem of the teensy.

#9

I checked the pwm pin without connected to the MC33926. The teensy pulls it always directly low when new sketch is uploaded. Only when connected with the MC it has the strange behaviour to keep the last pwm state and then pulling high.

#10

Hi.

The IN pins are both pulled high on the MC33926, so it makes sense that they would go high when your Teensy is not controlling them. That is why Derrill suggested using the D2 pin to disable the motor outputs while the driver is not being actively controlled. The D2 pin is pulled low by the MC33926 which disables the motor, so if you connect it to an I/O pin on your Teensy rather than directly to 3.3V, it will disable the outputs when the Teensy resets. Then you can use the Teensy to send it a high signal when you want to control the motor from your program.

-Claire

#11

Hey Claire,
thanks for that, I tried using the D2 as you suggested. But the problem remains.

#12

Can you post pictures of your setup that show how everything is connected when you are using D2? Can you use your scope to look at the voltage on the D2 pin when uploading a program?

-Claire