Innovations Embedded Controlling DC Brush Motors with H-bridge Driver ICs White Paper ROHM MarketingUSA Presented by ROHM Semiconductor Controlling DC Brush Motors with H-bridge Driver ICs Advanced-design integrated circuits combine control and protection functions; offer upgrade path from legacy designs and selection of control strategies Introduction H-bridge Basics DC brush motors are increasingly required for a broad The H-bridge circuit derives its name from the full-bridge range of applications including robotics, portable circuit shown in Figure 1. The motor forms the cross- electronics, sporting equipment, appliances, medical piece in the “H.” Speed and direction are controlled as devices, automotive applications, power tools and many current flows through the motor in the direction deter- others. The motor itself is a preferred alternative because mined by the position of the switches in the bridge. In it is simple, reliable and low cost. Equally important, this example, with switches “A” and “D” closed, the advanced, fully-integrated “H-bridge” driver ICs are avail- motor will operate in a clockwise (CW) direction. With able to control the motor’s direction, speed and braking. “B” and “C” closed, the motor will operate in the coun- This paper will explore the basics of H-bridge drivers terclockwise (CCW) direction. and discuss the advancement of the technology from discrete solutions to highly-integrated ICs. It will compare linear motor speed control with more advanced, higher-efficiency pulse-width modulation (PWM) techniques. The reader will be introduced to ROHM’s unique product family which incorporates numerous advanced features including high-efficiency PWM outputs, integrated timing and control circuitry as well as the unique capability of handling either analog or digital (PWM) speed control inputs. The paper will also describe the benefits of these Figure 1. Simplified H-bridge Schematic advanced motor driver ICs particularly in terms of their exceptional efficiency, integrated fault protection, small In the linear output control implementation, the motor package size, symmetrical pin configurations and pin- speed control is determined by the voltage applied compatibility with earlier (linear output) models. Finally, a across the motor. In the PWM implementation, the summary of the range of H-bridge ICs offered by ROHM speed is controlled by the width of series of pulses of including devices specified with 7 V, 18 V and 36 V equal voltage. In either case, motor direction is con- VCC, as well single packages containing two selected trolled via separate logic inputs. (matched) drivers is presented. ROHM Semiconductor H-bridge Driver ICs 1 While the concept is simple, implementation is any- takes advantages of the strengths of bipolar and CMOS thing but simple if discrete components are employed. design providing high drive capability and low power dis- Controlling the operation of the switches and prevent- sipation. A comparison of the power dissipation char- ing simultaneous closure of the CW and CCW control acteristics of linear H-bridge drivers vs. the latest PWM outputs, particularly when reversing the direction of the output drivers is shown in Figure 2. motor or changing speed by dynamic braking requires an H-bridge controller. The H-bridge controller is then connected to four devices forming the legs of the bridge. In a discrete solution the designer must deal with voltage control levels, timing to prevent shoot-through and the proper selection of the semiconductor switches. The discrete solution also requires additional circuitry for functions including overvoltage, overcurrent, overtem- Ongoing improvements in power MOSFETs have increasingly shrunk the die size to handle a particular voltage and low on-resistance. Today, control circuitry and the four output drivers are offered in surface mount packages comparable to or only slightly larger than only one of the output switches required in a discrete implementation. perature and electrostatic discharge (ESD) protection. All of this translates to a fairly complex design process resulting in a higher component count, larger footprint, and less reliable design solution than a fully-integrated LSI solution. x H-bridge Driver Topology x x x x Integrated H-bridge drivers are constructed by combining a controller, output drivers and protection circuits into a single package. The first H-bridge drivers used bipolar power transistors and bipolar control circuitry. Figure 2. Comparison of linear vs. PWM implementation. In the linear implementation, at anything but full speed, the voltage drop across the control transistors results in significant power dissipation. The bipolar outputs were typically operated in the linear mode to provide speed control. Simple IC processing In summary, the H-bridge motor driver IC provides a made the circuit practical even though die sizes were monolithic solution to the control and output functions large to optimize power dissipation. A limitation of the required to control the direction and speed of DC brush bipolar output devices was higher power dissipation, motors. We will now discuss the latest ROHM imple- especially in the speed control mode. mentation that allows designers to utilize a variety of The use of power MOSFETs for the output devices was control strategies, both analog and digital, while provid- a natural transition for H-bridge drivers. In addition to ing the precision and efficiency of PWM control. the lower losses for a given voltage rating and smaller die size, voltage-controlled MOSFETs are easier to drive than the current-driven bipolar switches, facilitating efficient PWM control. In addition to higher efficiency, PWM provides tighter motor speed control as well as faster response. BiCMOS design for the control portion ROHM Semiconductor H-bridge Driver ICs 2 The Ideal H-bridge Driver high side switches common in many integrated H-bridge With BiCMOS control and power MOSFET technology, the latest generation of ROHM devices represent the ideal integrated H-bridge driver. Figure 3 shows a block drivers. Rugged recovery diodes built into the structure eliminate the need for additional external recovery diodes. diagram of the functional elements. To handle either Combined bipolar and CMOS processing in a single chip analog or digital inputs, the unit provides dual-mode design achieves less than 1 µA current in standby mode. speed control. VREF provides the analog input. The chip This is an important consideration for portable, battery- converts the linear input at VREF into efficient speed con- powered applications. trol using its internal PWM conversion circuitry. FIN and To protect the motor and the driver, protective circuitry RIN are used with a microcontroller (MCU) or other digital includes: logic inputs to control direction and speed. Overvoltage protection (OVP) The control logic takes input from the analog and digi- Undervoltage lockout (UVLO) tal source and efficiently controls the forward / reverse Overcurrent protection (OCP) directions, speed and braking of the motor by switching Thermal shutdown (TSD) the appropriate integrated power MOSFETs. ROHM’s Overlap (shoot-through) protection P-Channel / N-Channel high-power CMOS output pro- High ESD protection (4 kV) vides low on-resistance without requiring a charge pump and the associated external capacitors needed for the N-Channel MOSFETs in the Figure 3. The ideal H-bridge driver includes flexibility for analog or digital operation and extensive protection circuitry. ROHM Semiconductor H-bridge Driver ICs 3 proper voltage operating range. OCP limits the current PWM Speed Control Techniques Using ROHM H-bridge Drivers draw and essentially shuts the device down by forcing all The latest ROHM H-bridge drivers provide PWM speed driver outputs into a high impedance state in the event control through a variety of techniques to address the of a short circuit or other excessive current event such requirements of different applications. Over- and undervoltage circuits keep the IC within its as a locked rotor. TSD protection can provide longer term protection when the chip is operating within its current capability but some other fault has occurred, such as an extremely high operating temperature environment or loss of adequate cooling in an enclosure or a MCU Control With an MCU or other digital logic providing the PWM input, a circuit like the one in Figure 4 would be appropriate. The pulse train applied to the FIN and RIN lines controls the direction and the speed digitally from the A) Regulated power supply deteriorated heatsink path. MCU. Table 1 shows the logic for implementing PWM in VREF From a timing standpoint, OCP is fast response protection and TSD is slower. For example, TSD provides back-up protection for faults that OCP cannot detect such as a soft short that is within the current limit but still causes an excessive temperature rise. OCP protects the MOSFET outputs and TSD protects the die. If the B) Unstable power supply VREF-PWM conversion circuit TSD OCP OVP UVLO VREF-PWM conversion circuit VREF TSD OCP OVP UVLO VCC VCC the forward and reverse directions as well as brake and FIN Controller RIN FIN CTRL LOGIC Controller CTRL LOGIC RIN GND GND idle values. To complete the application, the VREF is tied OUT1 M OUT1 OUT2 VREF setting by the resistance divider M OUT2 VREF setting by the zener diode to VCC and two external decoupling capacitors are conD) VREF setting by a D/A converter C) Soft start nected from VCC to motor and IC ground. VREF VREF-PWM conversion circuit TSD OCP OVP UVLO DAC Analog Voltage Control VREF-PWM conversion circuit VREF TSD OCP OVP UVLO VCC FIN Controller RIN VCC FIN CTRL LOGIC Controller CTRL LOGIC RIN GND GND die temperature exceeds a predetermined limit, such as With directional inputs provided through the FIN and RIN 175 ºC, the IC will shut off. pins according to Table 2, the VREF input can be used to For every H-bridge application, overlap timing circuitry is required to prevent shoot-through current spikes OUT1 OUT2 OUT1 M M OUT2 VREF setting by CR constant control the DC motor’s speed. 2) Direct PWM drive including replacement from low saturation type when switching direction or applying dynamic breaking. VREF-PWM ROHM H-bridge drivers control this internally. If an MCU VREF is used to directly control the output devices, a program must be written to ensure proper timing to avoid shoot- PWM Controller through problems. A thorough design includes ruggedness to handle unexpected occurrences damaging the driver such as ESD. L FIN RIN TSD OCP conversion VREF input control OVP UVLO circuit Input FIN RIN HCTRL L LOGIC Output VCC Forward L H Reverse H H Brake OUT1 GND M OUT2 L such L as an Idle Figure 4. A digital controller, MCU, can directly drive the control logic circuitry in the H-bridge driver. ROHM H-bridge ICs are specified to handle ESD volt- Direct PWM control Input FIN RIN PWM L ages as high as 4 KV. Output Forward L PWM Reverse H H Brake L L Idle Table 1. This table shows the application of the PWM pulse train and logic inputs to control speed, direction, and brake and idle status. ROHM Semiconductor H-bridge Driver ICs 4 diode in the lower leg of the voltage divider as shown in variable voltage source to the internal PWM circuitry. Figure 6. In spite of line voltage fluctuations, the motor This voltage could also be supplied from a variable volt- will be controlled at the same speed. A) Regulated power supply VREF-PWM conversion circuit VREF TSD OCP OVP UVLO B) Unstable power supply VREF-PWM conversion circuit VREF age source (potentiometer, resistor array) that allows for TSD OCP OVP UVLO VCC VCC operator control of the motor speed. This design works FIN Controller Simplified Digital Speed Control FIN CTRL LOGIC RIN Controller CTRL LOGIC RIN best with a regulated power supply. Note: a microcon- The output of a digital to analog converter (DAC) could troller is not required for this approach; the FIN and RIN drive the VREF providing the analog control voltage to the GND OUT1 inputs could come from two switches. GND OUT1 OUT2 M B) Unstable power supply Figure 7. D) VREF setting by a D/A converter C) Soft start VREF-PWM conversion circuit VREF FIN Controller OCP OVP UVLO TSD OCP OVP UVLO VCC DAC VCC Controller FIN OUT1 M Controller OUT2 Controller LOGIC RIN L VREF setting by CR constant VREF-PWM conversion circuit VREF DAC VREF Controller VREF setting by the zener diode M VREF-PWM conversion circuit TSD OCP OVP UVLO TSD OCP FIN RIN FIN Controller Idle OVP UVLO V VCC F Controller VCC CTRL LOGIC M RIN GND OUT1 conversion circuit VREF setting VREF Output M OUT2 GND VREF setting byOUT2 the resistance divider M OUT1 its target speed. Direct PWM control UVLO by CR constant Forward L PWM With the resistor divider inputReverse tied to VCC, if the line voltL PWM FIN Brake H H age changes, the motor speed will change. A CTRL fixed L Controller RIN 2) Direct PWM drive including replacement fromLOGIC low saturation Idle L L VREF-PWM conversion circuit VREF PWM speed can be accurately established with a Zener D) VREF settin C)OCP Soft start TSD OVP RIN Fixed Speed From FIN an Unregulated Supply FIN Controller TSD OCP OVP UVLO DAC VCC type F Controller GND OUT1 OUT2 M GND VREF-PWM conversion circuit TSD OCP OVP UVLO VREF VCC FIN Controller PWM Controller VCC TSD OCP OVP UVLO OUT1 OUT2 M VREF setting by CR constant CTRL LOGIC RIN GND VREF-PWM conversion circuit L VCC Figure 8. Adding a soft-start function simply requires adding a capacitor and two diodes. GND FIN OUT1 RIN M OUT2 CTRL LOGIC VREF setting by the zener diode 2) Direct PWM drive including replacement from low saturation type Figure 6. A Zener diode provides a reference for constant speed operation. D) VREF setting by a D/A converter DAC VCC VREF VREF-PWM conversion circuit ROHM Semiconductor FIN Controller RIN TSD OCP OVP UVLO VCC CTRL LOGIC GND OUT1 M OUT2 VREF H-bridge Driver ICs VREF-PWM conversion circuit TSD OCP OVP UVLO 5 PWM VR VCC CTRL LOGIC RIN B) Unstable power supply VREF R the full input. The motor starts slow and slowly reaches OUT2 Table 2. Truth table for the control of direction, brake and idle VREF-PWM status. Input B) Unstable p capacitor and two diodes so the voltage builds slowly to GND L OUT2 CTRL LOGIC 2) Direct PWM drive including Brakereplacement from low saturation type H H L GND The soft-start technique shown in Figure 8 uses a Reverse OUT1 OUT2 M Soft-Start Control with Analog Input VCC Forward H GND Figure 7. With a DAC, a digital voltage converted to analog can provide a input. D/A converter D) VREF setting the by VREF C) Soft start Output VCC OUT1 A) Regulated power supply Figure 5. Simple analog speed control using a voltage divider input. FIN RIN OUT1 M VREF setting by the resistance divider Input FIN RIN H L CTRL OCP UVLO VCC OUT2 TSD OCP VREF V-PWM REF input control conversion OVP UVLO circuit TSD OVP CTRL LOGIC GND OUT1 VREF OCP UVLO CTRL LOGIC RIN GND TSD OVP VREF-PWM conversion circuit VREF FIN CTRL LOGIC RIN VREF-PWM conversion circuit VREF CTRL LOGIC FIN Controller TSD VREF-PWM conversion circuit VREF RIN M OUT2 driver converting the signal intoVREF a PWM output in setting by the zenershown diode VREF setting by the resistance divider A) Regulated power supply stance divider Figure 5 shows a simple voltage divider providing the FIN R 7 V DC Low Voltage, Battery-powered 18 V DC Power supply and battery-powered 36 V DC Power supply and high voltage, battery-powered Robotics Cordless power tools Marine pumps Toys and games Instrumentation Automotive pumps Handheld printers Home appliances Automotive fuel cells Camera Lenses Vacuum pumps Automotive actuators Navigation systems Encoders Aerospace actuators Fans Auto antenna Security actuators Instrumentation Actuators Diaphram pressure pumps Medical pumps Pumps Power tools and robotics Radio antennas Sprayer and washer systems Gearbox drivers Actuators Micro motors in appliances (refrigerator) Vending machines Security locks Gearbox drivers Sporting Equipment Copiers Printers Fans Table 3. Popular applications for H-bridge drivers. Selecting the Right H-bridge Driver for the Application Low-Profile Packaging Due to the variance of operating voltages, in order to (some as thin as 1.5 mm), which is especially important provide the ideal solution it is important to pick the cor- in portable products. rect H-bridge driver. Table 3 shows several popular applications and voltage selection criteria. Multiple Voltage and Current Configurations Optimize Performance The low-profile ROHM packages are all within 2.2 mm Dual-Channel Versions Offer Matched Performance For applications requiring more than a single independently operated motor, such as printers, robotics, toys and games, ROHM’s dual-channel H-bridge drivers offer independent control of each channel in space saving To meet the requirements of these applications, ROHM offers H-bridge drivers rated for maximum operating voltages of 7 V, 18 V and 36 V with 0.5 A, 1.0 A and 2.0 A current ratings in single and dual channel packages. Typically, individual applications have operating voltages ranging between 3-5 V, 6-15 V or 18-32 V. However each ROHM driver operate with any VCC below its maximum limit. The lower VCC max. devices provide higher efficiency since the output MOSFETs trade off higher voltage with higher on-resistance. So selecting the packages featuring symmetrical pin configuration. Flexible Control Strategies ROHM H-bridge drivers provide several options for controlling direction, speed, brake and idle, as described in detail on pages 4-5, above. ROHM drivers feature an internal VREF to PWM conversion circuit for simple analog speed control in addition to digital input control levels of 2.0-5.0 V TTL from an external MCU. appropriate VCC max. optimizes the power consumption and avoids added expense for a higher voltage rating. ROHM Semiconductor H-bridge Driver ICs 6 Migration from Linear Control to PWM Putting It All Together The latest generation of ROHM H-bridge This paper has presented the basics of H-bridge driver drivers are pin-compatible with earlier models. technology and the important benefits of ROHM’s prod- Applications using VREF linear control can easily migrate uct family including: to the latest design without any modifications to an High efficiency existing PCB layout and obtain the advantages of PWM Minimal external components functionality. Low power consumption Many of these advanced PWM H-bridge drivers are pin Low power dissipation compatible with ROHM’s existing linear output line-up, Internal shoot-through protection providing added efficiency and eliminating the potential ESD protection for board placement errors. Fast response time Built-in fault protection To get more details on the complete line of ROHM H-bridge driver ICs, visit: www.rohmsemiconductor.com/h-bridge.html At this site you will find a comprehensive product selection guide, product datasheets and additional application information. ROHM Semiconductor H-bridge Driver ICs 7 10145 Pacific Heights Blvd., Suite 1000 San Diego, CA 92121 www.rohmsemiconductor.com | 1.888.775.ROHM NOTE: For the most current product information, contact a ROHM sales representative in your area. ROHM assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representations that the circuits are free from patent infringement. Specifications subject to change without notice for the purpose of improvement. The products listed in this catalog are designed to be used with ordinary electronic equipment or devices (such as audio visual equipment, office-automation equipment, communications devices, electrical appliances and electronic toys). Should you intend to use these products with equipment or devices which require an extremely high level of reliability and the malfunction of which would directly endanger human life (such as medical instruments, transportation equipment, aerospace machinery, nuclear-reactor controllers, fuel controllers and other safety devices), please be sure to consult with our sales representative in advance. © 2009 ROHM Semiconductor USA, LLC. Although every effort has been made to ensure accuracy, ROHM accepts no responsibility for errors or omissions. Specifications and product availability may be revised without notice. No part of this document represents an offer or contract. Industry part numbers, where specified, are given as an approximate comparative guide to circuit function only. Consult ROHM prior to use of components in safety, health or life-critical systems. All trademarks acknowledged.