DRV8308EVM: closed loop at slow speed, running problem

Michael Moskalenko

Prodigy 60 points

Part Number: DRV8308EVM
Other Parts Discussed in Thread: DRV8308

Hi,

i want spin my motor with closed loop. Speed range is 100 - 1400 rpm.

Start always with load at 100rpm.

The low starting speed is my problem.

The lowest start speed with closed loop i can realize is ~500rpm.

The Motor does not react if i choose a speed below 500rpm

My Motor: (4 Poles-Motor)

I use your TI development tool run the motor

this are the register-settings:

Speed change over a external CLK from function generator.

Is it possible to run such kind of motor at closed loop with 100rpm with the DRV8308 at all?

Can you check the Registers... maybe i missed something.

Best Regards

Michael M.

over 6 years ago

0 Adam Sidelsky over 6 years ago

TI__Guru 65190 points

Michael,

Closed loop operation is only guaranteed down to 50Hz. With an 8 pole motor, this equates to about 500 RPM. With a 4-pole motor, this is doubled to 1000 RPM. The motor can be run from PWM input at any speed, have you tried this? This is independent of the internal 50 Hz lower limit.

I also notice you are using a very very old GUI, Please use the new one here: dev.ti.com/.../DRV8308

Regards,

-Adam

0 Michael Moskalenko over 6 years ago in reply to Adam Sidelsky

Prodigy 60 points

Hello Adam,

thank you for the reply.

I tryed to run the motor with the PWM-Input. I can reach the 100rpm with about ~10% PWM.

But i need additional Hardware-performance from my µC to close the control loop. I can not use it this way.

Anyway i understood from your reply, that i can not run my motor with such low speed with the DRV8308.

You know any kind of device/ IC i can use instead of DRV8308?

Best Regards

Michael

0 Adam Sidelsky over 6 years ago in reply to Michael Moskalenko

TI__Guru 65190 points

Michael,

The internal speed loop has a minimum electrical frequency specification of 50Hz. If you need slower then you will need to go to a higher pole count motor.

Let me ask my colleagues.

Regards,

-Adam

0 Adam Sidelsky over 6 years ago in reply to Adam Sidelsky

TI__Guru 65190 points

Michael,

Typically for low speed operation, hall sensor operation is required. Does your motor have hall sensors or can you add them?

The DRV8308 accepts hall inputs directly.

At 100 RPM with your motor, you would need electrical frequency of around 3Hz which none of our parts can handle.

Regards,

-Adam

0 Adam Sidelsky over 6 years ago in reply to Adam Sidelsky

TI__Guru 65190 points

Michael,

I will close this thread due to inactivity, please post again if you have further questions.

Regards,

-Adam

Motor drivers

Motor drivers forum

DRV8308EVM: closed loop at slow speed, running problem