DRV8308 Change the speed issues

Mickey Zhang

Genius 12080 points

Other Parts Discussed in Thread: DRV8308

Hi team,

The customer is using DRV8308 EVM. In the "PWM Modes" , he can change the speed of motor anytime. In the "Clock Frequency Mode" , he can change the speed of motor when the frequency increases from 100HZ to 2KHZ.

But there is no change for the speed of motor when the frequency decreases from 100HZ,even if he change the clock value.

In the "Clock Frequency Mode" , the speed register is set 4094.

What is the reason? How to solve the issue?

Thanks,

Best Regards,

over 9 years ago

0 Phil Beard over 9 years ago

TI__Expert 4650 points

Hi Mickey,

What is the MINSPD register setting?

The AA_SETPT and AG_SETPT register settings should be smaller than the target minimum speed, so less than 100 Hz for this use case.

Decreasing the SPEED register value can also help the driver run motors at lower speeds by minimizing speed overshoot.

0 Mickey Zhang over 9 years ago in reply to Phil Beard

TI__Genius 12080 points

Hi Phil,
The customer said the MINSPD register value is the default. And the customer's issue is the speed is no-changed not the motor is not running
when the frequency decreases from 100HZ. Even if the clock value is 0, the motor is still running and the speed is no-changed.

0 Mickey Zhang over 9 years ago in reply to Phil Beard

TI__Genius 12080 points

Hi Phil,
Can you see my reply? email: [redacted]

0 Phil Beard over 9 years ago in reply to Mickey Zhang

TI__Expert 4650 points

Hi Mickey,

The default register value for MINSPD is 98, so the speed loop will ignore any CLKIN commands below a certain point once the motor has reached a LOCK state, so lowering the CLKIN below the MINSPD value will cause the driver to ignore those commands, MINSPD should be changed to a value lower than the default to allow for slower speeds.

Also AA_SETPT and AG_SETPT should be adjusted to fit in the lowest speed range needed for motor operation.

0 Mickey Zhang over 9 years ago in reply to Phil Beard

TI__Genius 12080 points

Hi Phil,
Thnaks for your reply.
How much are AA_SETPT and AG_SETPT? increased or decreased?

0 Phil Beard over 9 years ago in reply to Mickey Zhang

TI__Expert 4650 points

Hi Mickey,

I would decrease these values from the default. What is the minimum speed needed in this application?

Thanks,

Motor drivers

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DRV8308 Change the speed issues