DRV8308_15 Datasheet, PDF (19/60 Pages) Texas Instruments – DRV8308 Brushless DC Motor Controller

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DRV8308
SLVSCF7A – FEBRUARY 2014 – REVISED OCTOBER 2014
Standard 120° Commutation (DIR = 0)
State 1 2 3 4 5 6 1 2 3 4 5 6 1
Hall U
Hall V
Hall W
Phase U HS
Phase U LS
(1)
(1)
Phase V HS
Phase V LS (1)
(1)
(1)
Phase W HS
Phase W LS
(1)
(1)
(1) Low for Asynch Rectification, !PWM for Sync Rectification
Figure 8. Standard 120° Commutation (DIR = 0)
8.3.4.2 120° Single-Hall Commutation
To generate commutation timing for single-Hall commutation, a digital timer is used to create a clock that runs at
960× the Hall sensor frequency. Only one Hall sensor input, HALL_U, is used for commutation; this eliminates
any torque ripple caused by mechanical or electrical offsets of individual Hall sensors.
Single-Hall commutation is only enabled when the register BASIC = 0 and the motor is operating at a nearly
constant speed or speed-locked condition. To control this function, logic is used to determine when the speed is
constant and the speed control loop is locked. This logic generates the LOCK signal. The LOCK signal is also
output on the LOCKn terminal.
Except in PWM input modes, LOCK is also prevented from being signaled if the speed control loop integrator is
saturated (either at 0 or full-scale), which indicates that the speed control loop is not locked.
Until LOCK goes active (for example, at start-up, stop, or application of a sudden load that causes motor speed
to drop very quickly), standard 120° commutation is used. Because of this, three Hall sensors are required
regardless of which commutation method is used.
The commutation timer drives a counter that can be offset with a value programmed in the ADVANCE register.
This value allows the phase of commutation to be shifted relative to the actual Hall sensor transitions. Note that
the phase advance is not functional in standard 120° commutation. The phase advance also has an automatic
mode where the advance value is scaled according to motor speed (see Auto Gain and Advance Compensation).
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