TB6612FNG Vm and Vcc shorted?

hello, first time to post a topic here…

so i’ve hooked a TB6612FNG motor driver to a Arduino Nano, and have made a test code for functionality, connections are as follows (used to A channel only):

  • AIN1 to Nano pin 2
  • AIN2 to Nano pin 4
  • PWMA to Nano pin 3
  • A01 to motor + pin
  • A02 to motor - pin
  • VCC to Nano 5V
  • VM to Nano Vin pin to 7.6V (2x 18650 in series)

before i connect the USB cable to the PC to upload the test code, i removed the 18650 battery pack, leaving the VM pin connected to Vin pin, then i uploaded the code… after uploading the code, the motor runs, even though there should be no power to the VM pin… but when I remove the connection between the VM pin and the Vin pin, the motor stops

what do you think guys, was there a fault between the Vin pin and the 5V pin of the Nano? or somewhere else? Thanks in advance for your help :slight_smile:

Also, I tried to do the following to see where could be the culprit (Note: everything is under USB power)
*Vm to Vin disconnected, motor goes off
*Vm to Vin connected, motor runs
*Vcc to 5V connected or disconnected, nothing happens when Vm to Vin is disconnected
*Vcc to 5V connected, Vm to Vin connected, motor runs
*Vcc to 5v disconnected, Vm to Vin connected, motor runs (This part is where I am most confused, since there’s no Vcc for the TB6612FNG)

I’ll try to have voltage readings now.

Now i’ve measured the voltage across Vm and Gnd, with no voltage across vcc, and it says 3.6v… Now i dont know really what is the cause of this… Thanks in advance for the help


It sounds like you are noticing 5V USB power at VIN on your Arduino Nano, which is not surprising and fairly common behavior for the kinds of linear regulators used in this scale of electronics. If you do not want to see this behavior in your application, you can add a diode between VM and VIN (in a way that only allows current to flow from VM to VIN).

As for the motor running when VCC on the motor driver is disconnected, the motor driver could be getting its logic power from logic high signals on its input pins. By the way, sending logic signals to electronics while they are not powered (like you did by removing power to Vcc in your test) is not good and should be avoided.


I am also have same issue, but using external power, not USB power.

I wondering if I can use different voltage for VM… can I use diode between VM and VIn?

My battery voltage is 7.5V to VM pin and to fix 5V voltage regulator powering Arduino nano and TB6612FNG VCC.

When I disconnect VCC. No problem motor run forward and backward as expected.

When connect VCC to 5V (after regulator):

forward(leftMotor, rightMotor, 255);
back(leftMotor, rightMotor, -255); //my arduino some how reset it self at this point...

Hello, microvoice.

A diode might help in your situation, but it is difficult to be more certain without more specific details about your setup. Can you post a schematic that shows all of your connections? Can you also post a link to the datasheet or product page for your 5V regulator?

By the way. it sounds like you are saying that your motor driver is working fine when power is removed from VCC, which does not sound like a good state for the motor driver to be in. Like I mentioned earlier in this thread