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com TI Tech Note
Application Brief
Field Oriented Control (FOC) Made Easy for Brushless DC
(BLDC) Motors Using TI Smart Gate Drivers
Vashist Bist, Analog Motor Drives
Introduction can also allow motor to run above the nominal speed
using field weakening technique.
Brushless DC (BLDC) motors continue to grow in
popularity due to their high efficiency, high operating TI ± DRV8304 (Solution for FOC-BLDC)
Smart Gate Driver
speed, high flux density per unit volume, compact Gate Driver
size, low maintenance requirements and low electro-
magnetic interference (EMI) problems. For these
High Side VM
Charge-Pump High Side VDS Monitor
reasons, the BLDC motors are replacing the brushed
OCPHS +
+
± -
10V
DC (BDC) motors in a variety of applications such
RHS_SOURCE
VCP VM
DHS_BLOCK
as appliances, electric vehicles, medical applications, INHX
RHS_SINK FETHSA FETHSB FETHSC
heating ventilation and air conditioning (HVAC), RHS_PD
motion control and robotics, etc. The BLDC motor is a Low Side
Low Side VDS Monitor
BLDC Motor
three-phase synchronous motor with stator composed
Regulator
OCPLS +
+
of three-phase windings (concentrated windings for ±
10V RLS_SOURCE
-
VGSL
trapezoidal-BLDC motor and sinusoidally distributed RLS_SINK
DLS_BLOCK FETLSA FETLSB FETLSC
windings for sine-BLDC motor) and a rotor having
INLX
RLS_PD
permanent magnets (or vice versa in exterior rotor
PM motors). BLDC motors do not have mechanical
Current Sense Amplifiers with AUTOCAL
brushes and commutator assembly. Therefore, issues
RSENC
RSENA
RSENB
CSA-A
associated with BDC motors, such as wear and R1 R2 R3 R4
Gain
Settings
tear of the brushes, sparking concerns, and EMI
+
problems, are eliminated. This motor is also referred SOA
-
R9
R10
to as an electronically commutated motor, because +
- Gain
an electronic commutation based on the rotor position
R13 R12 Settings
R5 R6 R7 R8
VREF
is used rather than a mechanical commutation. The GND
rotor position of the BLDC motor is generally sensed SOB CSA-B
using the Hall-effect position sensors. SOC CSA-C
There have been numerous control algorithms
developed for controlling BLDC motors. The Figure 1. TI Smart Gate Driver for FOC
algorithms are typically classified based on the type Implementation
of BLDC motor (trapezoidal or sinusoidal), position
sensor requirements (sensored or sensorless) and The 3-phase BLDC motor needs a 3-phase voltage
speed and torque (current) control requirements. source inverter (VSI) to feed AC current to motor.
With the increased capacity of today's micro- The switches of this VSI are generally field effect
controllers, industry is expanding boundaries on the transistors (FETs) for low voltage applications (or
implementation of high-end control algorithms such Insulated Gate Bipolar Transistors - IGBTs for high
as field oriented control (FOC). FOC implementation power applications), which are driven by the gate
allows the BLDC motor to run more efficiently (high driver. Most gate drivers available today require
power factor and better light load efficiency), more external gate components (resistors and Zener
smoothly (lower torque ripples) with quick dynamic diodes) for operation and protection. However, TI's
response (better dynamic performance to load and Smart Gate Drive (SGD) technology eliminates
speed changes). FOC control makes the stator and external gate components as shown in Figure 1.
rotor magnetic field orthogonal to each other to With its adjustable gate drive currents (gate slew-
achieve the maximum electromagnetic torque. It uses rate control), the SGD architecture provides flexibility
a decoupled control of flux and torque due to which it in reducing electromagnetic interference (EMI). The
SLVA939B – JANUARY 2018 – REVISED AUGUST 2018 Field Oriented Control (FOC) Made Easy for Brushless DC (BLDC) Motors 1
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SGD architecture optimizes the dead time for a better • High operating switching frequency for achieving
efficiency while fully protecting the FET's to avoid any better noise performance
shoot-through conditions. A strong-pulldown current is • Adjustable slew rates for optimized EMI
also added for prevention of any spurious dv/dt gate performance
turnon. • Very low dead time for higher switching efficiency
• Very low propagation delay for better pulse-control
The DRV8304 device is a three-phase gate driver
accuracy and better dynamic response
based on the TI's Smart Gate Drive (SGD)
• Highly integrated driver and small package size for
architecture. The operating maximum voltage of 38-V
reduced board area
of this device is fully optimized for the 12-V and 24-
• Advance on-chip protection features and
V BLDC motor FOC application. DRV8304 support
diagnostics
external N-channel high-side and low-side power
MOSFETs and can drive up to 150- mA source, 300- Alternate Device Recommendation
mA sink peak currents with a 15-mA average output
Depending on the necessary system requirement,
current. DRV8304 is a highly integrated device which
there are additional devices available that may
includes gate driver supplies (high side charge-pump
provide the required performance and functionality.
and low side linear regulator), three current sense
For applications requiring detailed diagnostics and
amplifiers (CSA) and a 3.3-V, 30-mA regulator which
limp-home mode support, DRV8305 is recommended.
can be used for powering up the external controller.
DRV832x is preferred in the applications requiring
The integrated current-sense amplifiers (CSA) in a higher operating voltage such as 36-V battery
DRV8304 are used for sensing three phase currents operation.
of BLDC motors for optimum FOC and current-control
Table 1. Alternative Device Recommendations
system implementation. An adjustable gain settings
Device Optimized Parameters Performance Trade-Off
of 5, 10, 20 and 40 V/V provides a flexibility to user
for choosing the optimum sense resistor suiting the 45-V Abs-max Voltage
Limp-Home Mode Higher CSA Input Offset
end-application. The CSA can also be configured to DRV8305
1-A / 1.25-A (Source / No AUTOCAL feature
sense the unidirectional current which can be used in Sink) Gate Drive
implementing the current limit control for trapezoidal 65-V Abs-max Voltage
BLDC motor. The CSA in DRV8304 includes an 1-A / 2-A (Source / Sink)
DRV832x Higher CSA Input Offset
AUTOCAL feature which automatically calibrates the Gate Drive
CSA offset error at power-up for accurate current Integrated Buck Option
sensing. DRV835x 100-V Abs-max Voltage Higher CSA Input Offset
1-A / 2-A (Source / Sink)
Various PWM modes are available in DRV8304 Gate Drive
which make it an easy-to-interface driver. User Integrated Buck Option
has the flexibility to choose 6x or 3x mode
for the FOC (or sinusoidal current control), 1x Table 2. Adjacent Tech Notes
SBOA174 Current Sensing in an H-Bridge
mode for trapezoidal current control with on-chip
block-commutation feature and independent mode Low-Drift, Low-Side Current Measurements for
SBOA161
Three-Phase Systems
for driving the solenoids relays. A high level of
protection feature-set makes this device invulnerable Bi-Directional, Low-Side Phase Current Sensing
SBOA171
with Integrated Over-Current Detection
in any operating scenarios. These features include
power-supply undervoltage lockout (UVLO), charge- Low-Drift, Precision, In-Line Motor Current
SBOA160
Measurements With Enhanced PWM Rejection
pump undervoltage lockout (CPUV), VDS overcurrent
monitoring (OCP), gate-driver short-circuit detection
(GDF), and overtempertaure shutdown (OTSD) and
fault events are indicated by the nFAULT pin. A
summary set of features which makes DRV8304 an
ideal for BLDC motor FOC application is as follows.
• Optimized driver absolute maximum voltage (40-V)
for 12-V and 24-V BLDC motors
• Triple CSA for three phase BLDC motor current
sensing with 4 settings of gain selection
• AUTOCAL feature for reduced CSA input offset
error which provides better motor rotation jitter
performance
2 Field Oriented Control (FOC) Made Easy for Brushless DC (BLDC) Motors SLVA939B – JANUARY 2018 – REVISED AUGUST 2018
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