MCT8316Z datasheet(82/100 Pages) TI

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9.3 Typical Applications

9.3.1 Three-Phase Brushless-DC Motor Control With Current Limit

In this application, the MCT8316Z-Q1 is used to drive a brushless-DC motor with current limit up to 100% duty

cycle. The following design procedure can be used to configure the MCT8316Z-Q1 in current limit mode.

9.3.1.1 Detailed Design Procedure

Table 9-1 lists the example input parameters for the system design.

Table 9-1. Design Parameters

DESIGN PARAMETERS

REFERENCE

EXAMPLE VALUE

Supply voltage

VVM

24 V

Motor peak current

IPEAK

2 A

PWM Frequency

fPWM

50 kHz

Slew Rate Setting

200 V/µs

Buck regulator output voltage

VBK

3.3 V

9.3.1.1.1 Motor Voltage

Brushless-DC motors are typically rated for a certain voltage (for example 12 V or 24 V). Operating a motor at a

higher voltage corresponds to a lower drive current to obtain the same motor power. Operating at lower voltages

generally allows for more accurate control of phase currents. The MCT8316Z-Q1 functions down to a supply of

4.5V. A higher operating voltage also corresponds to a higher obtainable rpm. The MCT8316Z-Q1 allows for a

range of possible operating voltages because of a maximum VM rating of 40 V.

9.3.1.1.2 Using Active Demagnetization

Active demagnetization reduces power losses in the device by turning on the MOSFETs automatically when the

body diode starts conducting to reduce diode conduction losses. It is used in trapezoidal commutation when

switching commutation states (turning a high-side MOSFET off and another high-side MOSFET on while keeping

a low-side MOSFET on). Active demagnetization is enabled when EN_ASR and EN_AAR bits are set in the SPI

variant or MODE pin is set to Mode 5, Mode 6, or Mode 7 in the H/W variant.

When switching commutation states with active demagnetization disabled, dead time is inserted and the low-side

MOSFET’s body diode conducts while turning another high-side MOSFET on to continue sourcing current

through the motor. This conduction period causes higher power losses due to the forward-bias voltage of

the diode and slower dissipation of current. Figure 9-7 shows the body diode conducting when switching

commutation states.

MCT8316Z-Q1

SLVSGO3 – DECEMBER 2021

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