MCT8317A datasheet(46/161 Pages) TI1

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POWER_REF

POWER_MEAS

OUT

POWER_PI_OUT

VMAX

VMIN

Switch Close

If VMIN<OUT <VMAX

MEASURED INPUT

DC VOLTAGE

ESTIMATED

INPUT DC

CURRENT

DUTY CMD

MAX_POWER

Figure 8-33. Power Regulation

8.3.13 Anti-Voltage Surge (AVS)

When a motor is driven, energy is transferred from the power supply into the motor. Some of this energy

is stored in the form of inductive and mechanical energy. If the speed command suddenly drops such that

the BEMF voltage generated by the motor is greater than the voltage that is applied to the motor, then the

mechanical energy of the motor is returned to the power supply and the VM voltage surges. The AVS feature

works to prevent this voltage surge on VM and can be enabled by setting AVS_EN to 1b. AVS can be disabled by

setting AVS_EN to 0b. When AVS is disabled, the deceleration rate is configured through CL_DEC_CONFIG

8.3.14 Output PWM Switching Frequency

MCT8317A provides the option to configure the output PWM switching frequency of the MOSFETs through

PWM_FREQ_OUT. PWM_FREQ_OUT has range of 5-100 kHz. In order to select optimal output PWM switching

frequency, user has to make tradeoff between the current ripple and the switching losses. Generally, motors

having lower L/R ratio require higher PWM switching frequency to reduce current ripple.

8.3.15 Fast Start-up (< 50 ms)

MCT8317A has the capability to accelerate a motor from 0 to 100% speed within 50 ms. This will only work

on low inertia motors which are capable of this level of acceleration. In order to achieve fast start-up, the

commutation instant detection needs to be configured to hybrid mode by setting INTEG_ZC_METHOD to 1b. In

the hybrid mode, the commutation instant is determined by using back-EMF integration at low-medium speeds

and by using built-in comparators (BEMF zero crossing) at higher speeds. MCT8317A automatically transitions

between back-EMF integration and comparator based commutation depending on the motor speed as shown

in Figure 8-34. The duty cycles for commutation method transition at lower speeds are directly configured by

INTEG_DUTY_THR_LOW and INTEG_DUTY_THR_HIGH and at higher speeds are indirectly configured by

INTEG_CYC_THR_LOW and INTEG_CYC_THR_HIGH. These duty cycles should be configured to provide a

sufficient hysteresis band to avoid repeated commutation method transitions near threshold duty cycles. The

BEMF threshold values used to determine the commutation instant in the back-EMF integration method are

configured by BEMF_THRESHOLD1 and BEMF_THRESHOLD2.

MCT8317A

SLLSFQ2 – JANUARY 2023

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