DRV10964 Datasheet, PDF (15/27 Pages) Texas Instruments – Three-Phase Sinusoidal Sensorless BLDC Motor Driver

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Device Functional Modes (continued)
60 degrees
DRV10964
SLDS227 – MARCH 2016
±
V
+
U
+
W
±
Figure 15. Initial Speed Detect Function
The motor speed is determined by measuring the time between two rising edges of either of the comparators.
If neither of the comparator outputs toggle for a given amount of time (80 ms), the condition is defined as
stationary and the Align state will begin. If the comparators are toggling at a speed that is greater than this
threshold then the DRV10964 will wait for the motor to slow down until the toggling is less than the threshold and
it can be treated as stationary.
7.4.1.4 Align
To align the rotor to the commutation logic the DRV10964 applies a 50% duty cycle on phases V and W while
holding phase U at GND. This condition is maintained for 0.64 seconds. In order to avoid a sudden change in
current that could result in undesirable acoustics the 50% duty cycle is applied gradually to the motor over 0.3
seconds.
7.4.1.5 Handoff and Closed Loop
When the motor accelerates to the velocity defined by the voltage applied to the CONFIG pin, commutation
control transitions from open loop mode to closed loop mode. The commutation drive sequence and timing is
determined by the internal control algorithm and the applied voltage is determined by the PWM commanded duty
cycle input.
The selection of handoff threshold can be determined by experimental testing. The goal is to choose a handoff
threshold that is as low as possible and allows the motor to smoothly and reliably transition between the open
loop acceleration and the closed loop acceleration. Normally higher speed motors (maximum speed) require a
higher handoff threshold because higher speed motors have lower Kt and as a result lower BEMF. Table 2
shows the configurable settings for the handoff threshold. Maximum speed in electrical hertz are shown as a
guide to assist in identifying the appropriate handoff speed for a particular application.
Table 2. Motor Handoff Speed Threshold Options
MAXIMUM SPEED (Hz)
350 to approximately 400
<100
100 to approximately 150
150 to approximately 200
200 to approximately 250
250 to approximately 300
300 to approximately 350
350 to approximately 400
400 to approximately 450
450 to approximately 500
Hand Off Frequency (Hz)
87.5
12.5
25
37.5
50
62.5
75
87.5
100
112.5
CONFIG[3:0]
0x0
0x1
0x2
0x3
0x4
0x5
0x6
0x7
0x8
0x9
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