Reduced board space in brushed DC motor driver designs

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Low cost and simplicity of control make brushed DC motors suitable for use in automotive applications such as window regulators, sunroof controls, locks, latches and motor valves. However, designing swept DC motor drivers imposes several challenges, including size constraints and the ability to respond appropriately to fault conditions. Additionally, you’ll want to pursue design-reuse strategies to reduce development time.

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Integrated small package

To optimize your design, start with a device such as the DRV8243-Q1 Automotive 40V, 12A H-Bridge Driver from Texas Instruments. (Fig. 1). The device incorporates built-in current regulation and a current feedback pin, eliminating the need for external current sense resistors, reducing board space and reducing costs.

Available in a lead-free flat quad HotRod automotive package as small as 3×4.5mm, the DRV8243-Q1 features built-in field-effect transistors (FETs), helping you save board space by eliminating the need for external FETs and gate drivers. The device is available in two interface options: the hardware (HW) version uses fixed-configuration jumper resistors, while the Serial Peripheral Interface (SPI) version offers more flexibility in configuration and observability at the using an external microcontroller.

The DRV8243-Q1 includes several diagnostic and protection features to help you design a system that can handle various fault conditions. For example, it provides open-load detection and short-circuit protection in both on and off states, using a network of passive resistors to identify system problems before activating the FETs. (Fig.2). The SPI option provides detailed diagnostic information to help identify the type of fault and its location, saving you time and money when troubleshooting.

All DRV8243-Q1 family members share similar package firmware, features, and pinouts to facilitate design reuse across a range of current levels and load types, including relays and solenoids as well as engines, all of which can exist in an automotive subsystem. When used in independent mode, one DRV8243-Q1 can drive two unidirectional brushed DC motors, two solenoids, or two relays, saving space by eliminating the need for two separate half-bridge drivers .

Evaluation module

To help you get started with designs based on the DRV8243-Q1, TI offers the DRV8243H-Q1EVM evaluation module (Fig.3) plus software written in TI GUI Composer to control the module. You can run a cloud-based version of the software directly from a Chrome-based browser or download a version that can be installed on your computer. In addition to the DRV8243-Q1 motor driver, the module includes an MSP430G2553 microcontroller to control the driver and an MSP430F5528 microcontroller that handles UART and JTAG communications via USB.

The module has several connectors. A micro-USB connection serves as the primary communication interface between the module and your PC and allows for microcontroller firmware updates. A supply voltage ranging from 4.5 to 36 Vdc from a battery or DC power supply connects to a screw terminal block. (The module provides fuse protection and reverse polarity protection.)

Bi-directional brushed DC motors connect to the banana jacks labeled OUT1 and OUT2. High-side or low-side switched loads (for example, unidirectional brushed DC motors or solenoids) can connect to banana jacks labeled Ground and VM.

Gate Drivers and Motor Drivers

In addition to the DRV8243-Q1 40V, 12A H-bridge driver, TI offers a full line of other motor drivers as well as gate drivers. In the latter category, the DRV8701 47-V H-bridge smart gate driver can drive four external N-channel FETs (Fig.4). It has built-in PWM current regulation and can limit motor inrush current.

Additionally, the gate driver offers a low-power sleep mode and incorporates two LDO voltage regulators to power external components. Protection features include power supply undervoltage lockout, charge pump undervoltage lockout, and overcurrent protection (OCP).

Additional H-bridge motor drivers with built-in FETs include the DRV8251A 50V, 4.1A; the 40V, 21A DRV8244-Q1; and the 35V, 3.7A DRV8231, which like the DRV8243-Q1 all have built-in current sensing and feedback. The 50V, 4.1A DRV8251 also has built-in current sense and feedback, but adds a latched OCP function.

All of these devices help you reduce system complexity and board size through innovative packaging and high levels of integration. Features such as low conductor activation resistance (RDS(ON)) and ultra-low standby current modes help you increase efficiency and extend battery life. In addition, accurate current sensing provides precise position and torque control. Finally, built-in protection features provide robust protection for your motor systems and intelligently diagnose fault conditions.

Technical resources

TI offers many resources to ensure design success. TI Precision Labs’ comprehensive online classroom, for example, offers a variety of sessions, starting with an introduction to its comprehensive engine driving program. The program includes a course that describes the construction of brushed DC motors, explains how mechanical commutation works, and examines how brushed DC motors compare to stepper motors and brushless DC motors.

Another session describes the H-bridge circuit, which takes its name from its resemblance to the letter H (Fig.5). The session instructor explains how the H-bridge can control the flow of current to a load and drive a motor back and forth. He notes that NMOS FETs are often used for switches because, for a given size, they have a lower RDS(ON) value compared to PMOS FETs. However, NMOS FETs require a higher gate drive voltage.

Still other sessions cover topics ranging from the importance of back EMF to the use of pulse width modulation, providing a comprehensive overview of brushed DC motor control.

Conclusion

System size, diagnostic and protection features, and design reusability are key factors to keep in mind when choosing motor drivers. TI offers a full line of motor control products to optimize your application, and the company’s evaluation modules and comprehensive technical support help you achieve design goals quickly and accurately.

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