MCF8316C-Q1: Increase speed command resolution to achieve stable 14400RPM

Tony Lee98

Part Number: MCF8316C-Q1
Other Parts Discussed in Thread: MOTORSTUDIO

Tool/software:

Hi,

My customer is using the MCF8316C to run the motor PLL spin at 14,400 RPM to control a BLDC motor, and we have concerns about speed command resolution.

When validating speed command resolution using the GUI I2C interface, we found that the actual usable speed command is only 8-bit. Additionally, the PWM-based speed command from the MCU (10 kHz) also confirms that the speed command resolution is 8-bit. Based on previous experiments, an 8-bit speed command resolution cannot achieve stable motor index PLL control at 14,400 RPM.

Questions:
1. Does MCF8316C have other methods to increase speed command resolution?
2. Are there other TI's BLDC motor drivers that support higher resolution?

1 month ago

0 Venkatadri Shantaram84961 1 month ago

TI__Mastermind 26012 points

Hi Tony Lee

What is the speed command mode? Is this PWM?

Please refer to the table below for effective number bits

Also, please note with internal oscillator mode we may see up to 2.5% speed error across temperature range,

With external clock we can improve the accuracy to 1%.

Thanks and Best regards

Venkatadri S

0 JS Chuang 1 month ago in reply to Venkatadri Shantaram84961

Prodigy 40 points

Hello, Venkatadri
Please focus on I2C mode first. PWM mode is used to double-check the resolution of the "Speed_Ctrl" register. When I use MotorStudio to set the speed according to the "Speed_Ctrl" register value shown in the table above, I find that the lower bits (bits 0-6) of Speed_Ctrl are different(6C7F/6C40/6C01/6C00), but SPEED_REF remains unchanged. Therefore, the effective number of bits in Speed_Ctrl is 8.
Is this correct?

0 Venkatadri Shantaram84961 1 month ago in reply to JS Chuang

TI__Mastermind 26012 points

Hi JS,

Is this using REF_PROFILE? What is the mode of REF_PROFILE?

Can you share me the JSON?

In REF_PROFILE mode Duty and Speed are 8 bit.

Thanks and Best regards

Venkatadri S

0 JS Chuang 1 month ago in reply to Venkatadri Shantaram84961

Prodigy 40 points

The "Ref Profile Config" is set to "Linear Profile" and the config file is attached file.

How can I set config to use higher bit than 8bit.

register_New1001_0951.csv

0 Venkatadri Shantaram84961 1 month ago in reply to JS Chuang

TI__Mastermind 26012 points

Hi JS,

Change the REF_PROFILE_CONFIG to Reference/Equation mode. Any other mode will use the REF_PROFILE registers, which have an 8-bit width.

Thanks and Best regards

Venkatadri S

0 Venkatadri Shantaram84961 24 days ago in reply to Venkatadri Shantaram84961

TI__Mastermind 26012 points

Hi JS,

Any update on this?

Thanks and Best regards

Venkatadri S

0 JS Chuang 24 days ago in reply to Venkatadri Shantaram84961

Prodigy 40 points

Hello, Venkatadri

After the setting changes to Reference/Equation mode, the motor can now lock the phase stably

0 Venkatadri Shantaram84961 23 days ago in reply to JS Chuang

TI__Mastermind 26012 points

Hi JS,

Thanks for the confirmation, please can we close this thread?

Thanks and Best regards

Venkatadri S

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MCF8316C-Q1: Increase speed command resolution to achieve stable 14400RPM