DRV10974: DRV10974 12-V, Three-Phase, Sensorless BLDC Motor Driver

Hi Michel,

  As per datasheet in pin description it is written that it is internal pull to 2.2V, we thought if we didn't connect anything motor will rotate at full speed. Is it ok if connect PWM pin to 3.3V instead of 1.8V to have 100% duty cycle.

for DRV10970 if  PWM pin is floating the motor is rotating at full speed.

Regards,

Sayali

Hey Sayali,

This is the part of the datasheet I was referring to. This is for the min/max voltage of the DRV10974 when configured for analog PWM. Can you check if the speed input is configured to analog mode?

Regards,

Michael

Hello Micheal,

          In DRV10970 evaluation board we had kept PWM pin (pin no 19) open ,that time motor was rotating at full speed i.e at 100% duty cycle.

Is same thing applicable to DRV10974 IC , if we didn't apply any input to PWM pin (pin no 4)  the motor will rotate at full speed?.

if not is it ok if we give 3.3V to this pin so that motor will rotate at full speed , earlier you said analog input range is up to 1.8V only.In datasheet in recommendation section the voltage range against pin is upto 5.5V.

we want to rotate motor at full speed ,we don't want any pwm or analog control for our application .we will control speed by varying input voltage.

please suggest what best thing we can do with pwm pin  to achieved this .

Regards,

Sayali

Hi,

We do not recommend applying 5.5V on the PWM pin as this is the ABS max voltage that can be applied to the pin. We also do not recommend applying 3.3V to this pin because 1.8V is the max recommended voltage on this pin.

Please try to pull the PWM pin to 1.8V. This will ensure that 100% duty cycle is applied at power up. 

Thanks,

Michael

Hi Michael,

I have following two questions.

  1. As you explain the motor will rotate at full speed at 1.8V so higher than this is not recommended.

but in datasheet it is mentioned that it is internally pull up 2.2V. Please see below picture.

2. Can we leave this pin not connected since it is already internally pull up.

Regards,

Sayali 

Hi Sayali,

It's a valid question, I will check this on the bench on Monday. I will follow up with you at that time.

Thanks,

Michael

Hi Sayali,

I just ran this experiment in the lab. I set up the EVM such that it was in PWM mode (not analog). PWM pin has 3V on it and motor spins when power is applied. So there is no need to apply additional voltage to this pin. Does this resolve your issue, or is there anything else I can assist with?

Regards,

Michael