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Texas Instruments Small Motors in Large Appliances Application notes
Small Motors in Large Appliances
Vashist Bist, Analog Motor Drives
Introduction
A recent trend has been seen in appliances (both
large-home and small-home appliances) for moving
from high-voltage (HV) motors to low-voltage (LV)
motors for low power application (<100-W). This
transition is due to availability of low power drivers
which have the following advantages over high voltage
systems.
• High Integration: Highly integrated motor drivers
with driver which include the power-stage,
regulators and controllers in a single package
• High Protection and Diagnostics: Integrated
protection features with detailed diagnostics
• Better Control: With low voltage application, the
current requirement increases which allows an
accurate sensing and control of motor currents
• Reduced Size / Low Form-Factor: LV drivers
have low creepage and clearance needs
• Reduced Design Time: Integration helps in plug
and play designs
• Low Cost: Reduced size saves on PCB, and no
high-voltage components are required which are
costlier than low voltage components
• Safety: Low voltage is safe for humans
Low voltage brushed DC and stepper motors are
increasingly being used in large-home appliances.
There are numerous applications requiring brushed
DC motors such as ice-makers and ice-crushers in
refrigerators, cleaning motors in air-conditioners, dryerfan motors, detergent dispensers and door-lock motors
in dish-washers / washers and dryers. The brushed
DC motors also finds applicability in self-cleaning
applications in cooking ranges and water valves in
residential water heaters. Moreover, the applications
which requires a precise control of position such as the
damper motor for refrigerant flow-control in
refrigerators or the louver motors in air-conditioners for
air-flow control uses stepper motors. A lot of lowvoltage brushed and stepper motor are also finding
applicability in small-home appliances such as the
coffee-machines, vacuum cleaners, fans, air-purifiers,
mixers, blenders and food processors. This Tech-Note
targets motor driver for these applications which
requires a low voltage (<20-V) and a low power motor
(<12-W).
SLVA977 – July 2018
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Internal
Regulators
Charge Pump
(Internal)
Power Supply
(UVLO)
VM
GND
MODE
VM
TRQ
OUT1
nSLEEP
IN1
IN2
Logic
+
Control
IN3
Gate
Drive
+
OCP
+
OLD
OUT2
OUT3
OUT4
IN4
nFAULT
Over
Temperarture
Current
Regulation - 34
ISEN34
Current
Regulation - 12
ISEN12
Figure 1. High Integration in Motor Drivers
A full bridge is required for bi-directional control of
brushed DC motor; whereas, two full bridges are
required to control of a bipolar stepper motor. The fullbridge enables the operation of brushed-DC motor in
either of four different modes such as the forwarddirection mode, reverse-direction mode, coastingmode (fast-decay) and brake-mode (slow-decay). The
motor (BDC or stepper) is expected to work in any of
these modes or the combination of these modes to
achieve current regulation.
The DRV8847 device is a highly-integrated dual fullbridge (H-bridge) motor driver with integrated FETs as
shown in Figure 1. This device supports a minimum
voltage of 2.7-V and maximum voltage of 18-V and
fully-optimized for the 12-V DC input voltage
applications. It consists of a fully-integrated chargepump to drive 8-NMOS FETs in two full bridges. The
charge-pump in DRV8847 doesn't require any external
capacitors, thus saving the BOM cost and design
complexity. This device consists of internal low onstate resistance (RDS(ON)) FETs which allows to drive 1A current per full-bridge.
The DRV8847 device has four interface options which
provides a flexibility to connect different type of loads.
Each of the four modes is optimized for the type of
load, performance requirements and the number of
controller GPIO resources. The interfaces are
classified based on the type of load as shown in
Table 1.
Small Motors in Large Appliances Vashist Bist, Analog Motor Drives
Copyright © 2018, Texas Instruments Incorporated
1
www.ti.com
Table 1. Type of Loads and Interface Options
Operation
Interface
GPIO
Requirements
Full-Step
2-Pin
2-Pins
Half-Step
4-Pin
4-Pins
2 Motors
Independent
4-Pin
4-Pins
1 Motor (High
Current)
Parallel
2-Pins
Independent
Half Bridges
Independent
1-Pin /
Solenoid
Motor Type
Stepper Motor
Brushed DC
Motor
Solenoids
Loads
Fast Decay
(All FETs in Hi-Z state)
ITRIP
Motor
Current
Driving Mode
(Forward /
Reverse)
Slow Decay
Both Low-Side
FETs ON
25%
tON
75%
tOFF
(Mixed Decay)
Time
VM
Figure 3. Current Limit Operation in DRV8847
OUT1
Bridge-12
IN1
IN2
To
Load
Control
+
Gate-Drive
OUT2
ISEN12
TRIP
±
Digital Noise Filter
Comparator
+
REF
(VTRIP)
Current Regulation - 12
Figure 2. Current Regulation in Full Bridge of
DRV8847
The device contains integrated protection features to
alert the system of any abnormal condition. These
protection features include power-supply undervoltage
lockout (UVLO), overcurrent protection (OCP) on each
FETs, open load detection (OLD) for detection of any
OUTx pin dis-continuity, and over-temperature
shutdown (OTSD) for protecting against high
temperatures. All the fault events are reported on the
nFAULT pin which can be monitored by external
controller.
The device also integrates the current regulation
feature for limiting the motor current. Figure 2 shows
the block diagram of the current regulator circuit
(single full-bridge) in DRV8847. As shown in this
figure, a sense-resistor connected on the source of the
low-side FETs is used to sense the bridge current.
This sense voltage is compared to an internal
reference trip-voltage (VTRIP) to control the bridge state.
Once, the current limit is hit, the bridge operates in
fast-decay (coast-mode), followed by a slow-decay
(brake-mode) to achieve current regulation as shown
in Figure 3. This current regulation features enables
the motor driver to limit the starting inrush current of
brushed DC motor and for achieving current limit for
stepper motor.
2
DRV8847 device also comes with a I2C interfacevariant (DRV8847S) which provides a detailed
diagnostics, high configurability and control of the
driver. In DRV8847S, many extra features are enabled
over I2C bus such as bridge control, bridge operation
selection in open-load / over current scenarios, current
decay settings, slew-rate configurability and detailed
diagnostics of the faults on registers. The DRV8847S
device also allows a multi-slave operation, by which
multiple devices can be controlled via a single I2C bus.
Such feature reduces the peripheral (GPIO)
requirements from the controller, reduces controller
cost and simplifies the driver boards design. With such
high level of integration, protection and configurability,
this device becomes a easy plug and play option for
the user driving variety of loads.
Alternate Device Recommendation
Depending on the necessary system requirement,
there are additional devices available that may provide
the required performance and functionality. For
applications requiring micro-stepping control of stepper
motor and adaptive current decay (AutoTune),
DRV8846 is recommended.
Table 2. Alternative Device Recommendations
Device
DRV8846
Optimized Parameters
Supports 1/32 Microstepping for Stepper
Motor
Supports Adaptive
Current Decay
(AutoTune) for Lower
Current Ripple
Performance Trade-Off
Brushed-DC motors and
Solenoid Loads are Not
Supported
Table 3. Related Documentation
SLVA504
Calculating Motor Driver Power Dissipation
TIDA-00297
Refrigerator Damper and Fan Motor Control
Solutions
Small Motors in Large Appliances Vashist Bist, Analog Motor Drives
Copyright © 2018, Texas Instruments Incorporated
SLVA977 – July 2018
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