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MCT8316A: Tuning steps

Marcel van den Heuvel
Prodigy 235 points
Part Number: MCT8316A

Hi All,

I am working on a battery powered device, and the battery voltage is directly fed to the MCT8316A. It's ranging from 17V to 12V. 

The motor that is connected has the following specifications:

Winding

25

x dia.

0.2

 

Supply voltage

14.8

[V]

 

EMFp-p

1.82

[Vrms p-p] bij 3000rpm

Rp-p

2015

[mOhm]

 

Lp-p

241

[uH]

 
Max RPM 17000 [RPM]
Magnet pairs 6

I have used the MCT8316A Tuning Guide to quick-start driving the motor. I've set the MAX SPEED to 25600 (resulting in a max RPM of 16000)

The settings in the MCT are:

REG_ISD_CONFIG 
0x6F04C100
REG_MOTOR_STARTUP1 0x3908D197
REG_MOTOR_STARTUP2 0x2110D590
REG_CLOSED_LOOP1 0x093F2200
REG_CLOSED_LOOP2 0x02A6E4B0
REG_CLOSED_LOOP3 0x4CC40101
REG_CLOSED_LOOP4 0x000CE944
REG_CONST_SPEED 0x00A00504
REG_CONST_PWR 0x320042C0
REG_DEG_TWO_PH_PROFILE 0x36DB6DA6
REG_DEG_THREE_PH_PROFILE 0x36DB6D80
REG_TRAP_CONFIG1 0x054BA105
REG_TRAP_CONFIG2 0x2A880000
REG_FAULT_CONFIG1 0x211042C0
REG_FAULT_CONFIG2 0x78F43025
REG_PIN_CONFIG1 0x2D720642
REG_PIN_CONFIG2 0x080C0000
REG_DEVICE_CONFIG 0x06720000
REG_GD_CONFIG1 0x1C440000
REG_GD_CONFIG2 0x14200000

When sending a low speed command, the following happens: 

The motor starts spinning open loop. When switiching to closed loop, it goes well. 

When increasing the speed command to higher values the motor starts speeding, but the current consumption increases and the motor is burning up. This while the ILIMIT value is set to 0.2V, and CSA_GAIN is set to 0.15 V/A. 

The maximum current should be around 1.3A, and the PSU is limited at 1.5A. (because 2 motors are burned already).

What can there be done to decrease the current? Higher modulation frequency? 

Thanks for any input!

Marcel

  • 0
    TI__Mastermind 24740 points

    Hi Marcel,

    Higher PWM switching frequencies will lead to greater losses by the internal FETs, I would recommend trying to use a PWM frequency such as 30 kHz to start.

    I also noticed that the CLOSED_LOOP_MODE is set to Disabled, in REG_CONST_SPEED, I would recommend trying to set this to Speed Loop or Power Loop to regulate the speed and/or current.

    Regards,

    Joshua