SLVSCF7B – FEBRUARY 2014 – REVISED NOVEMBER 2017
Application Information (continued)
Figure 25. 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
Figure 26. 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.
8.1.3 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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