MCF8316AEVM: How to control the SPEED of Motor Through the I2C Communication

Hi,

Anyone can Help here .?

Hi Ketan,

Thanks for your question on the Motor Drives E2E Forum. 

I will aim to provide an answer on this by the end of the week!

Best,

Robert

Hi Ketan, 

Please review section 7.3.8.3 I2C based Speed Control of the datasheet featured below:

Also check out the Register Field Descriptions here:

Best,

Robert

Hi Robert,

This I know, The Question is about calculating the DIGITAL_SPEED_CTRL Bits Value.

How to calculate the Value for DIGITAL_SPEED_CTRL Bits. 

Hi,

Thank you Noted.

We are able to control the motor speed with I2C Register, I feel that while writing to DIGITAL_SPEED_CTRL value it's fine, device operate the motor as soon as I write value into DIGITAL_SPEED_CTRL but when we write zero value into DIGITAL_SPEED_CTRL to stop the motor, it's taking much time, even it's not stopping the motor once DIGITAL_SPEED_CTRL update with zero value. I2C Operation is fine, able to read and write. 

We should apply the ACCESS KEY after the shadow Register Update. ? or MCF will read the shadow automatic and do the operation.? 

Hi Ketan,

If setting the speed command to zero is not slowing the motor down fast enough there is a BRAKE pin feature that I encourage you to look at (Section 7.3.16 - 7.3.19.6). You can also discover more about the braking methods here: https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1212192/faq-sensorless-bldc-trap-and-field-oriented-control-foc-motor-stop-options

However, it seems that you believe that setting DIGITAL_SPEED_CTRL to zero is taking time because of the I2C read and write operation. Let me investigate and get back to you beginning of next week.

Best,

Robert

Hi

Thank you for update..

I'll look into this article and try to understand the flow. Please let me know if any update on I2C side.

Can you confirm that while writing zero to DIGITAL_SPEED_CTRL bits, what should be the 31th bit of the Register. 

Hi Ketan,

The 31st register of the ALGO_CTRL1 register is an override bit used to control the SPD_CTRL bits. Are you wondering what to do specifically when writing zero to DIGITAL_SPEED_CTRL?

Please reference register field descriptions below:

Best,

Robert

Hi.

Yes I wondering that should I make it to zero because while writing non zero value to DIGITAL_SPEED_CTRL bits, I written with 1 on 31th bit. As per the datasheet, it's say that SPEED_ CMD= 0 for stand-by mode.

Hi Ketan,

You can leave bit 31 set to 1 and even when you apply SPEED_CMD = 0, it will just enter standby mode as you mentioned after tenSB:

Best,

Robert

Hi.

Okay Got it.

Then it's confirmed that it is taking much time after upading zero to DIGITAL_SPEED_CTRL bits.

Still we didn't apply Break-pin for stand-by mode so trying with only DIGITAL_SPEED_CTRL. Please let me know if any another method to enter in standby made.

It's Remote control FAN so that's is mandatory to enter to stand-by more after pressing the OFF Button on Remote side, It's doesn't make sense if OFF taking much time to switch off the FAN.

Hi Ketan,

Are you doing auto read fault status, auto read motor status, and auto read all registers during motor operation? This could be causing an I2C overload:

Is this issue still seen when using the speed pin in analog mode? Are you reading multiple I2C registers during the motor operation?

Best,

Robert

Hi,

No I am not doing any operation with I2C. I just Initialize the value to shadow register and apply the Access key at begging of the program. so that also once in while. i am writing to speed register only when OFF Button is pressed on Remote till that time there is no operation on I2C. 

Hi Ketan,

Thanks for the information. I will get back to you on this next week.

Best,

Robert

Hi Ketan,

I am still working on this debug please allow us until end of next week.

Best,

Robert

Hi Ketan,

When a 0% speed command is provided while motor is spinning, the device will utilize the motor stop option configured by MTR_STOP to stop the motor. This is different from the motor brake applied when the BRAKE pin is driven high, which can be configured to be either Low side braking or Align braking through BRAKE_PIN_MODE.

Could you please check what is your MTR_STOP option set to?

(Please note that there's an errata #7 in the MCF8316A where the Recirculation mode doesn't work properly.)

If you need faster motor stop (speed command set to 0 while motor is spinning), I would recommend selecting Low side or High side braking as the motor stop option.

Next, start by setting BRAKE_SPEED_THRESHOLD to 50%. If the stop time is too high, it is recommended to increase the threshold. However, setting speed threshold to higher speed would result in FETs carrying large current. So if there are any hotspots identified in the FETs, it is recommended to decrease the threshold.

The MTR_STOP_BRK_TIME can also be configured to control how long the low-side or high-side brake is applied.

Please refer to the datasheet section 7.3.19 Motor Stop Option for more details. Again, ignore the Recirculation Mode section due the the errata.

Regards,
Eric C.

Hi

Thank you for details explanation regarding motor operation. Let me investigation configuration one more time as you said, I will check the  MTR_STOP and BRAKE_SPEED_THRESHOLD option in configuration. I will update you by end of the week. We are busy for internal testing and training.

Thank you Eric C

Hi Ketan,

We will leave this thread open until you are able to confirm your investigation.

Best,

Robert

Hi,

Currently we moved to another project. you can close the thread for now. If any question is required I will reopen it. 

Thank you.

Hi Ketan,

Thanks for the update.

Best,

Robert