DRV8308_15 Datasheet, PDF (12/60 Pages) Texas Instruments – DRV8308 Brushless DC Motor Controller

DRV8308
SLVSCF7A – FEBRUARY 2014 – REVISED OCTOBER 2014
8 Detailed Description
www.ti.com
8.1 Overview
The DRV8308 device controls 3-phase brushless DC motors using a speed and direction input interface and Hall
signals from the motor. The device drives N-channel MOSFETs with 10-V V_GS, and a configurable gate drive
current of 10 to 130 mA.
There are three modes of speed input: clock frequency, clock duty cycle (pulse-width modulation), and an
internal register that specifies duty cycle. In the Clock Frequency Mode, the device’s digital speed control system
matches motor speed with the input clock’s frequency. Motor speed is either determined from the Halls sensors
or signal on the FG input, which can be generated from a board trace underneath the motor that senses
magnetic reluctance. The speed control system offers digital tuning of pole and zero frequencies and integrator
gain. When properly tuned, the DRV8308 can drive motors with < 0.1% cycle jitter and fast torque compensation
for varying loads. The duty cycle speed modes operate in open-loop without speed control.
When the DRV8308 device powers up, the configuration registers are set from either the one-time programmable
(OTP) non-volatile memory, or from an external EEPROM (depending on the SMODE terminal). After power-up,
registers can be set in realtime over SPI, and the OTP memory can be permanently written once.
When the DRV8308 device begins spinning a motor, it initially uses all three Hall sensor phases to commutate.
After a constant speed is reached, the LOCKn terminal is pulled low and only one Hall sensor becomes used;
this feature reduces jitter by eliminating the error caused by non-ideal Hall device placement and matching. Also
at this time, commutation transitions to sine wave current drive (if enabled), which minimizes acoustic noise and
torque ripple. Commutation timing can be tuned using the ADVANCE register for optimal performance and power
efficiency.
Numerous protection circuits prevent system components from being damaged during adverse conditions.
Monitored aspects include motor voltage and current, gate drive voltage and current, device temperature, and
rotor lockup. When a fault occurs, the DRV8308 device stops driving and pulls FAULTn low, in order to prevent
FET damage and motor overheating.
The DRV8308 device is packaged in a compact 6 × 6-mm, 40-terminal QFN with a 0.5-mm terminal pitch, and
operates through an industrial ambient temperature range of –40°C to 85°C.
12
Submit Documentation Feedback
Product Folder Links: DRV8308
Copyright © 2014, Texas Instruments Incorporated