DRV8308_15 Datasheet, PDF (43/60 Pages) Texas Instruments – DRV8308 Brushless DC Motor Controller

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Application Information (continued)
DRV8308
SLVSCF7A – FEBRUARY 2014 – REVISED OCTOBER 2014
INP
OUTN Hall
Sensor
INN
OUTP
Optional
VREG
xHP
xHN
+
Hall
Amp
-
Figure 26. Hall Sensor Connections
Since the amplitude of the Hall sensor output signal is very low, often capacitors are placed across the Hall
inputs to help reject noise coupled from the motor PWM. Typically capacitors from 1 to 100 nF are used.
Some motors use digital Hall sensors with open-drain outputs. These sensors can also be used with the
DRV8308 device, with the addition of a few resistors:
All Resistors 1 to 4.7 k
VREG
VCC
Hall
Sensor
GND
OUT
To Other
xHN Inputs
xHP
xHN
+
Hall
Amp
-
Figure 27. Hall Resistors
The negative (xHN) inputs are biased to 2.5 V by a pair of resistors between VREG and ground. For open-
collector Hall sensors, an additional pullup resistor to VREG is needed on the positive (xHP) input. Again, the
VREG output can usually be used to supply power to the Hall sensors.
9.1.3 FG Amplifier Configurations and Connections
To improve speed control by providing a higher bandwidth speed feedback, often a magnetic pickup coil,
commonly referred to as an FG generator, is used. This is typically implemented as a serpentine PCB trace on
the motor PCB. This generates a low-level sine wave signal whose amplitude and frequency is proportional to
the speed of the motor.
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