MCT8316A: Current limit for startup and continuous operation

Tomer Cohen

Part Number: MCT8316A

Tool/software:

Hi ,

We are operating a motor using the MCT8316A driver. The nominal current consumption of the motor is ~200mA, and we would like to limit it to 800mA.

The default settings from the guided tuning ended with CSA_GAIN=0.15V/A, OL_ILIMIT=0.4V and CBC_ILIMIT= 0.2V (meaning ~2.7A limit at open loop and 1.33A limit at closed loop).

When trying to change the current limit to 0.8A, I have changed the CSA_GAIN to 0.6V/A, OL_ILIMIT to 0.6V and CBC_ILIMIT to 0.5V. After the change, the motor failed to start, although no high currents were detected. the LOCK_ILIMIT register is set to 0.9V.

Can you please guide me through the current limitation procedure? Is there an additional change I should make to adapt the driver to the new CSA_GAIN set?

Thanks

Tomer

2 months ago

0 Venkatadri Shantaram84961 2 months ago

TI__Mastermind 23682 points

Hi Tomer,

What is the LOCK_ILIMIT_DEG time? What is motor R, L values?

OILIMIT sets 1A, CBC_ILIMIT for 0.8A which is correct as per the configuration.

If LR is such that there can be current overshoot and deglitch is too low.

Can you capture waveform, set trigger on the phase current to view the width?

Thanks and Best regards

Venkatadri S

0 Tomer Cohen 2 months ago in reply to Venkatadri Shantaram84961

Prodigy 20 points

Hi Venkatadri,

The LOCK_ILIMIT_DEG time is 75 msec. R=5.7Ohm, L=4.8mH

I will try to increase it and update if it is resolved.

Tomer

0 Tomer Cohen 2 months ago in reply to Tomer Cohen

Prodigy 20 points

Hi Venkatadri,

I have changed the FAULT_CONFIG1 register to 0x1B7A58B4(ILIMIT = 1.5V, ILIMIT_DEG 2.5 seconds) and the motor still cannot start at medium torque.

Please advise,

Thanks,

Tomer

0 Venkatadri Shantaram84961 2 months ago in reply to Tomer Cohen

TI__Mastermind 23682 points

Hi Tomer,

I will provide more pointers, quick question are you still seeing ILOCK fault?

Thanks and Best regards

Venkatadri S

0 Venkatadri Shantaram84961 1 month ago in reply to Venkatadri Shantaram84961

TI__Mastermind 23682 points

Hi Tomer,

What is the PWM frequency, can you change PWM frequency to 20kHz?

The default frequency is 40kHz , sometimes TBLANK and TDEG may not be sufficient if there is ringing in the PWM, hence reduce to 20kHz which will also improve the torque.

Thanks and Best regards

Venkatadri S

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MCT8316A: Current limit for startup and continuous operation