DRV8308: Motor Rise and Fall Time while changing speed

Ahmed Hussein

Part Number: DRV8308

Currently we are using DRV8308 to control Blower "Brushless DC Motor" to control air flow the motor is working smoothly and transitions is smooth

our main problem now is Rise and Fall time while changing speed we are using Driver register to control motor speed and it takes about 600 ms to change speed from 0.2 to 0.8 of full speed

we tried to modify driver registers and adjust settings but without any success time transition still the same

is there any configuration or settings to reduce that time we need it to be less than 100 ms?

over 2 years ago

0 Joshua Horlander Cruz over 2 years ago

TI__Mastermind 24570 points

Hi Ahmed,

I will aim to get you a response by next Wednesday.

Regards,

Joshua

0 Ahmed Hussein over 2 years ago in reply to Joshua Horlander Cruz

Prodigy 10 points

Hi Joshua,

ok thanks, waiting for it.

best Regards,
Ahmed

0 Joshua Horlander Cruz over 2 years ago in reply to Ahmed Hussein

TI__Mastermind 24570 points

Hi Ahmed,

I recommend tuning the LOOPGAIN and AUTOGAIN register values, if you have not already, to try and achieve a faster rise and fall time. To help with tuning these register values please refer to section 4.2 of the DRV8308 User Guide.

You could also try adjusting the IDRIVE strength to try and get a faster MOSFET rise/fall time, for assistance on tuning IDRIVE this please see this FAQ.

Regards,

Joshua

0 Ahmed Hussein over 2 years ago in reply to Joshua Horlander Cruz

Prodigy 10 points

Dear Joshua,

thanks for your reply

I made tuning again and increased IDRIVE but still have the same results around 600 ms to reach 0.8 of full speed.
currently we are using DRV8308EVM board to control the motor to avoid any hardware that might cause this problem

My question is that normal to have that much time?

any other recommendation would be appreciated

thanks

0 Ahmed Hussein over 2 years ago in reply to Ahmed Hussein

Prodigy 10 points

Dear Joshua,

I don't know if this screenshot would help but this the view of time transition

0 Joshua Horlander Cruz over 2 years ago in reply to Ahmed Hussein

TI__Mastermind 24570 points

Hi Ahmed,

Does the motor break quickly or is it as slow as when it is accelerating?

Could you provide a capture of your phase current when the motor is accelerating?

Could you also provide your systems nominal voltage and peak current?

Regards,

Joshua

0 Ahmed Hussein over 2 years ago in reply to Joshua Horlander Cruz

Prodigy 10 points

Hi Joshua,

1- for the motor break it takes around half the time of acceleration as attached pic
2- I will try to afford capture for phase current but currently I don't have the required tools to get a graph
3- System nominal Voltage 24V - Peak Current 1.8A

here are some of motor parameters that might help
Rated speed 33000rpm
Rated current ≤1.8A
inductor 200-260uH
pole pairs 2
Maximum speed 50000rpm

0 Ahmed Hussein over 2 years ago in reply to Joshua Horlander Cruz

Prodigy 10 points

Dear Joshua,

was wondering if we can directly modify driver PID control gains ?

thanks

0 Joshua Horlander Cruz over 2 years ago in reply to Ahmed Hussein

TI__Mastermind 24570 points

Hi Ahmed,

There are two adjustable gains in the DRV8308 are the LOOPGAIN and the SPEEDGAIN. For more information on these and what they affect please see the answers in this E2E. For some other general guidance on tuning parameters and their affects please refer to this E2E.

Just to mention, the speed loop on this device is only enabled when using the CLKIN control method.

Regards,

Joshua

0 Ahmed Hussein over 2 years ago in reply to Joshua Horlander Cruz

Prodigy 10 points

Dear Joshua,

After many trials and modifying mentioned parameters we still couldn't get faster time than we have

Is there any other method or trial we can try?
would you recommend changing the driver to another one which directly control rise time? if so any specific part number?

0 Joshua Horlander Cruz over 2 years ago in reply to Ahmed Hussein

TI__Mastermind 24570 points

Hi Ahmed,

We have many drivers in our MCx profile which are simpler to tune and offer a greater degree of control over the rise time.

I would recommend taking a look at the MCx8315 devices based on your required voltage and power level. The MCT8315A uses a trapezoidal algorithm and the MCF8315A uses a FOC algorithm.

Regards,

Joshua

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DRV8308: Motor Rise and Fall Time while changing speed