MCT8316A: Is it possible to change the control cycle of recognize the speed input?

Kenji

Part Number: MCT8316A

Hi Team

There is about 50ms of delay, from sending speed input until the motor actually start moving.
Below figure is the result of sending speed input via I2C. The delay time is same, in case send speed input via Analog or PWM.

Since the delay time is the same regardless of the speed input method, I think that delay is due to the control cycle of the device.

I want to know the control cycle of recognize the speed input (I think it is 20Hz from the result).
And I want to know if it possible to shorten the delay.

FYR, I'm using PMCT8316A for now.

over 3 years ago

0 Vishnu Balaraj over 3 years ago

TI__Mastermind 24415 points

Hi Kenji-san,

We would recommend to use MCT8316A (Production device) as we have fixed several bugs and made several improvements. Delay in production device should be less than 10 ms.

Regards,

Vishnu

0 Kenji over 3 years ago in reply to Vishnu Balaraj

Intellectual 530 points

Hi Vishnu Balaraj-san

I'm already trying to order at the TI store.
But, as you know, it is difficult to obtain parts now.

By the way, what is the cause of this delay?

0 Venkata Pavan Mahankali over 3 years ago in reply to Kenji

TI__Prodigy 530 points

Hi Kenji- San,

Can you check what is the (STARTUP_BRK_TIME) used in the ISD_CONFIG register. This configuration is used to brake the motor for a defined time at start-up. This ensures the motor is stationary before starting the motor with Align/IPD etc.. Apart from this there is a fixed startup delay of 15ms expected for device calibration.

0 Aaron Barrera over 3 years ago in reply to Venkata Pavan Mahankali

TI__Mastermind 26046 points

Hi Venkata,

Vishnu will get you a reply tomorrow.

THanks,
Aaron

0 Vishnu Balaraj over 3 years ago in reply to Aaron Barrera

TI__Mastermind 24415 points

Kenji-san,

Did you get a chance to check the recommendations from Venkata Pavan?

Regards,

Vishnu

0 Kenji over 3 years ago in reply to Vishnu Balaraj

Intellectual 530 points

Hi Vishnu Balaraj - san, Venkata Pavan Mahankali - san

50ms is setting.

I changed this value, but dead time will not be shortened.
Below is the result of START_UP_BRK_TIME=1ms.

Also, I tested with enable and disable STAT_BRK_EN, but dead time will not be shortened.

0 Vishnu Balaraj over 3 years ago in reply to Kenji

TI__Mastermind 24415 points

Kenji,

Looks like you are measuring the time between issuing I2C speed command and the open loop. Please note that before open loop operation, the device goes through startup mechanism to identify initial rotor position through IPD or align the rotor to a known position through Align/double align or slow first cycle.

What is the startup method you are using in your application? Using "Slow first cycle" as the startup method can get the motor to start spinning after the fixed startup delay.

Regards,

Vishnu

0 Kenji over 3 years ago in reply to Vishnu Balaraj

Intellectual 530 points

Hi Vishnu Balaraj -san

I'm testing step input under closed-loop control.
Acceleration of 2.5k rpm(10%) to 22.5krpm (90%) and deceleration of 22.5krpm to 2.5krpm.

So I think open loop and startup mechanisum is unrelated.
In additon, there is a about 50ms of dead time in deceleration too.

About startup method, my setting is "slow first cycle frequency".
By the way, there was no change in the dead time even if the setting was changed to "0Hz".