DRV10987 Datasheet, PDF (38/69 Pages) Texas Instruments – DRV10987 12- to 24-V, Three-Phase, Sensorless BLDC Motor Driver

DRV10987
SLVSE89 – AUGUST 2017
www.ti.com
S1
S3
S5
V_CC
M
S2
S4
S6
S1
S3
S5
V_CC
M
S2
S4
S6
Driving
AVS State
Figure 37. Inductive AVS
In this example, current is applied to the motor through the high-side driver on phase U (S1) and returned
through the low-side driver on phase W (S6). The high-side driver on phase U is turned off and after a period of
time (to allow the inductive energy in the resulting LR circuit to decay) the low-side driver on phase W is turned
off. If BrkDoneThr[2:0] = 000, no brake is applied and the device does not protect from inductive energy even
with the inductive AVS feature enabled.
8.4.10 PWM Output
The DRV10987 device has 32 options for PWM dead time. These options can be used to configure the time
between one of the bridge FETs turning off and the complementary FET turning on. Deadtime[4:0] can be used
to configure dead times between 40 and 1280 ns. Take care that the dead time is long enough to prevent the
bridge FETs from shooting through.
The DRV10987 device offers two options for PWM switching frequency. When the configuration bit PWMFreq is
set to 0, the output PWM frequency is 25 kHz, and when PWMFreq is set to 1, the output PWM frequency is 50
kHz.
8.4.11 FG Customized Configuration
The DRV10987 device provides information about the motor speed through the frequency generate (FG) pin. FG
also provides information about the driving state of the DRV10987 device.
8.4.11.1 FG Output Frequency
The FG output frequency can be configured by FGcycle[3:0]. The default FG toggles once every electrical cycle
(FGcycle = 0000). Many applications configure the FG output so that it provides two pulses for every mechanical
rotation of the motor. The configuration bits provided in the DRV10987 device can accomplish this for 2-pole, 4-
pole, 6-pole, and 8-pole motors up to 32-pole motors. This is illustrated in Figure 38 for 2, 4, 6, and 8-pole
motors.
Figure 38 shows the DRV10987 device has been configured to provide FG pulses once every electrical cycle (4
poles), twice every three electrical cycles (6 poles), once every two electrical cycles (8 poles), and once every
three electrical cycles (12 poles). [Text says 4, 6, 8, 12 poles. Figure says 2, 4, 6, 8 poles.]
Note that when it is set to two FG pulses every three electrical cycles, the FG output is not 50% duty cycle. Motor
speed is able to be measured by monitoring the rising edge of the FG output.
38
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