MCT8317A datasheet(43/161 Pages) TI1

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Phase

PHASE VOLTAGE

PHASE CURRENT

15 deg

30 deg

15 deg

Commuta on point

Back-EMF zero crossings

Figure 8-29. 150o commutation

Note

Different modulation modes are supported only with 120o commutation; variable commutation uses

mixed modulation mode only.

8.3.10.3 Lead Angle Control

To achieve the best efficiency, it is often desirable to control the drive state of the motor so that the motor

phase current is aligned with the motor BEMF voltage. MCT8317A provides the option to advance or delay the

phase voltage from the commutation point by adjusting the lead angle. The lead angle can be adjusted to obtain

optimal efficiency. This can be accomplished by operating the motor at constant speed and load conditions and

adjusting the lead angle (LD_ANGLE) until the minimum current is achieved. The MCT8317A has the capability

to apply both positive and negative lead angle (by configuring LD_ANGLE_POLARITY) as shown in Figure 8-30

Lead angle can be calculated by {LD_ANGLE x 0.12}o; for example, if the LD_ANGLE is 0x1E and

LD_ANGLE_POLARITY is 1b, then a lead angle of +3.6o(advance) is applied. If LD_ANGLE_POLARITY is

0b, then a lead angle of -3.6o(delay) is applied.

Note

For 120o commutation, the negative lead angle is limited to -20o; any lead angle lower than that will be

clamped to -20o.

For variable commutation, negative lead angle is not supported and positive lead angle is limited

to +15o. Anything configured higher than +15o or lower than 00 will be clamped to 15o and 0o

respectively.

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MCT8317A

SLLSFQ2 – JANUARY 2023

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