ROHM Knowledge Center
Resistive Touchscreens
Given the recent proliferation of touchscreens in everyday consumer and commercial devices, it seems surprising to learn that the first touchscreen was invented sometime between 1965-1967 by E. A. Johnson at the Royal Radar Establishment - a capacitive type designed for air traffic control. It wasn't until a few years later that the first resistive touchscreen was invented. Since then a number of other touchscreen technologies have surfaced, including infrared, acoustic wave, and optical.
Resistive Touchscreens (continued)
However, resistive touch remains the technology of choice for many applications, particularly industrial and commercial equipment due to its greater reliability, accuracy, and lower costs. One disadvantage inherent with previous resistive touchscreens was the inability to support multitouch (using two or more fingers) operation. This is no longer the case as some suppliers now offer resistive touchscreens and touchscreen controllers that provide multitouch capability, including gesture recognition similar to capacitive touchscreen products.
Although there are a variety of resistive touchscreen systems, all of them share common design elements. They are composed of two flexible sheets coated with a resistive material separated by a narrow gap. Touching the top sheet with an object such as a finger or stylus connects the two layers, which sends signals to the controller that converts the voltages to determine the precise location of the touch.
Several resistive touch technologies exist, including 4-wire, 5-wire, 8-wire, and digital matrix types. The simplest, 4-wire, is probably the most common due to its relatively low cost and time-tested design. As its name implies, it uses 4 wires, two each attached to the top and bottom sheets. A voltage gradient is then applied horizontally and vertically, one at a time, in order to determine the x and y coordinates. However, this method is restricted to displays less than 11 inches. 5-wire and 8-wire technologies are typically used with larger screens, although they entail greater costs. 8-wire in particular is gaining acceptance, since it provides greater versatility than 4-wire while providing greater (long-term) stability and accuracy than 5-wire types. Digital matrix technology is relatively more expensive, though it typically does not require a controller, making it easier to use, is completely customizable, and does not require recalibration.
In summary, while there are many types of touchscreen technologies available, each with drawbacks and advantages, resistive types continue to command the most market share, due in large part to an ideal balance between cost, durability, reliability, and precision. Plus, manufacturers are continually making refinements, breakthroughs, and innovations that are addressing many of the concerns of resistive touchscreens.
In the end, it is the responsibility of the designer to precisely define application requirements and carefully consider the pros and cons of each touchscreen technology in order to select the optimum solution to fit set needs.
ROHM Introduces Industry's First Multi-Touch Controller for Resistive Touchscreens
Less expensive than conventional capacitive touchscreen control; internal CPU supports dual-touch gesture sensing without external resistors; built-in compensation circuits facilitate volume manufacturing.
The new BU21023/BU21024 series of high-speed, high noise immunity, low-voltage resistive touchscreen controllers is now available from ROHM Semiconductor. These new controllers are the industry's first to enable multi-touch (two-point) operation and intuitive gesture control, including pinching, spreading and rotating – previously possible only with more expensive capacitive touch systems.
Block Diagram: BU21023GUL Multi-Touch Controller for Resistive Touchscreens
LED Driver Topologies
Regardless of type or application, all LEDs are current-driven devices whose brightness is proportional to their forward current. And although LEDs can be powered using a voltage source and a ballast resistor, the preferred way consists of a constant current source, such as an LED driver. This is because even small changes in forward voltage can result in a large change in forward current and, subsequently, brightness. Also, depending on the input voltage, power dissipation due to voltage drop across the ballast resistor wastes power and reduces battery life.
LED Driver Topologies (continued)
Unlike standard power supply ICs that provide constant voltage over a range of currents, LED drivers provide a constant current, which eliminates changes in current due to variations in forward voltage, ensuring constant brightness. Typical features include dimming capability (i.e. PWM) and protection circuits such as overvoltage/current and thermal shutdown.
Several LED driver topologies exist, each with advantages and drawbacks. The simplest solution for step-down (input voltage>LED voltage) operation utilizes a linear regulator, which has the additional benefits of low parts count and low EMI (Electromagnetic Interference). However, disadvantages include tight voltage requirements and relatively low efficiency – especially at higher currents – requiring impractical thermal countermeasures.
The more efficient option is through switching regulators, which operate by interrupting the power flow and control the conversion duty cycle in order to achieve a particular output current. Energy is stored in inductors or capacitors, ensuring high conversion efficiency across a wide input/output range. In addition, unlike linear regulators, different configurations exist, depending on the operation desired, such as boost (step-up), buck (step-down), and boost-buck. A couple of drawbacks exist, however, including relatively higher costs and lower reliability due to increased complexity as well as switching noise.
For applications where the input voltage always exceeds the LED voltage, a buck regulator is the preferred choice, since it features high reliability and performance with minimum component count, supports different dimming techniques, and provides high efficiency, eliminating the need for a heat sink.
For applications where the minimum forward voltage of all LEDs in a string exceed the maximum input voltage a boost (step-up) topology is required. Boost regulators are more difficult to design than buck regulators and require careful review of the specifications to ensure that internal current limits are never exceeded. In addition, unlike buck regulators boost configurations require an output capacitor to maintain constant current.
Finally, for applications where the input/output voltages overlap the buck-boost type is often used (although other topologies exist, such as SEPEC, Cuk, and Zeta). Parts count is similar to buck and boost systems, making it cost-effective. However, like their boost counterparts a capacitor is required for continuous output current and dimming is not as efficient as with buck systems. Another disadvantage is that Vo is inverted with respect to Vin, necessitating level shifting or polarity inversion.
As we can see, many types of LED drivers exist, each with different advantages and drawbacks. Several key factors must be taken into account when selecting the ideal solution for a particular application in order to maximize efficiency and performance, including the power source (i.e. AC mains, battery, low-voltage DC), input/output voltage ranges, dimming/isolation requirements, cost effectiveness, and power demands.
ROHM LED Driver Targets Automotive Headlamp Cluster Functions
ROHM Semiconductor's BD8381EFV-M is a high-brightness LED driver for automotive forward illumination applications. With this new flexible IC, designers can now specify the same driver for use in high-beam, low-beam and daytime running light (DRL) circuits.
The BD8381EFV-M current-mode buck/boost controller provides stable operation over a wide input voltage (5-30V) and removes constraints on the number of LEDs in series connection. Integrated protection monitors voltage, current and temperature. LED open and short circuit detection is also provided. The BD8381EFV-M has an internal PWM controller so dimming functions can be implemented with a simple external CR circuit. This same circuit can be implemented to limit output current in case of LED overtemperature detection.
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Distribution Spotlight
High Power Isolated Constant Current LED Driver for Illumination
Developed using energy saving technologies adopted from AC/DC converter designs, the BP5843A constant current LED driver seamlessly integrates all control circuits, switching elements, transformers, and constant current circuits required for LED drive into a compact, isolated SIP form factor.
Key Features:
- Wide input voltage range
- Constant current output optimized for driving LEDs
- Superior power conversion efficiency
- Compact SIP11 package with built-in switching transformer reduces the number of external parts
- Minimal output current fluctuation over a wide range of ambient temperatures
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Ultra -Low Ohmic Chip Resistors
Unique trimless design ensures greater current detection accuracy These products feature a resistive element comprised of a metallic substrate with superior electrical characteristics. An original structure is utilized for low resistance values (1mΩ to 10mΩ).
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Block diagram: BD8112EFV-M Can Drive 150mA through Two LED Lines & Requires a Minimal Number of External Components
ROHM Silicon Carbide Schottky Diodes Push the Performance Envelope
ROHM Semiconductor announces the availability of the SCS1xxAGC series of high-performance silicon carbide (SiC) Schottky barrier diodes (SBD). This new class of SiC diodes offers industry-leading low forward voltage and fast recovery time, leading to improved power conversion efficiency in applications such as PFC/power supplies, solar panel inverters, uninterruptible power supplies, air conditioners and others.
For a white paper, product selection guide and data sheets click here.
Next-Generation Compound Semiconductors
SiC, or silicon carbide, also known as carborundum – named from the combination of carbon and corundum (the natural form of alumina) – was first discovered by the American inventor Edward G. Acheson in 1891 while attempting to create artificial diamonds by mixing alumina and carbon. At around the same time Henri Moissan of France found a small sample in a meteorite in Arizona. Naturally occurring moissanite is extremely rare on Earth (but common in space) and is found only in minute quantities. As a result, virtually all silicon carbide sold, including moissanite jewelry, is manmade.
SiC first saw widespread use as an abrasive due to its extreme hardness (9 on the Mohs scale), durability, and low cost. Additional properties include low density, high strength, low thermal expansion, and high thermal conductivity. As such, it is utilized in a wide variety of applications, such as high performance brakes, bulletproof vests, turbine components, nuclear fuel particles, mirrors for telescopes, printmaking, and even jewelry (it is similar in appearance and hardness to a diamond).
Remarkably, the first LED was created using SiC in 1907 and the first commercially available LEDs were based on SiC. However, production has since been reduced dramatically due to the emergence of GaN (Gallium Nitride), which exhibits significantly brighter emission characteristics. SiC remains viable for use as a substrate for GaN active layer epitaxy, although sapphire has been proven a more attractive alternative and high quality bulk (free-standing) GaN wafers is becoming more readily available.
The wide bandgap properties of both SiC and GaN make them especially suited not only for optoelectronics, but high power, high frequency devices as well. Both GaN and SiC offer substantially higher electron mobility than Si, allowing for higher frequency operation. Thermal conductivity is also superior to silicon, meaning that GaN and SiC devices can theoretically operate at higher power densities. In addition, the high critical electric field allows operation at higher voltages and lower leak currents.
However, production hurdles must be overcome in order to realize semiconductor devices utilizing these two materials – in particular GaN, which requires either an SiC or Si substrate for wafers larger than 2". This heteroepitaxial (different substrate) structure limits GaN to lateral device fabrication and restricts its use to optoelectronics and HEMTs (High Mobility Electron Transistors). In contrast, homoepitaxial (same substrate) SiC is possible and allows for vertical topologies, enabling the development of MOSFETs and similar devices such as BJTs and JFETs [although there has been progress developing GaN MOSFETs grown on sapphire via MOCVD (Metal-Organic Chemical Vapor Deposition) using SiO2 as a gate dielectric].
In summary, both materials are promising successors to silicon and are expected to see wide use in next-generation semiconductor devices, with GaN ideal for high frequency applications and SiC better suited for power devices.
Infrared Technology for Sensing and Remote Control Applications
Breakthrough IR wavelength emitter technology has resulted in the development of IR emitters that operate near 850nm. This is much closer to the 800nm peak sensitivity of phototransistors, resulting in higher output efficiency and 66% less energy consumption than conventional emitters that operate at around 950nm.
More Info.DMOSFETs Deliver a Breakdown Voltage of 600V and an ON-Resistance of 0.4 Ω
ROHM's new DMOSFETs, developed utilizing SiC, offer 10 times lower ON-resistance than equivalent silicon DMOSFETs. Switching times are also reduced by more than 5 times compared with silicon IGBTs. This results in dramatically lower loss and enables smaller components to be used, minimizing board size.
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Stepper Motor Drivers for Optimum Performance
ROHM high-reliability Stepper Motor Drivers (BD638xx/BD642x/BD6290 series) offer exceptional performance features for printers and copiers, scanners, security cameras, robotics, sewing machines, factory automation and other precision motor control applications.
These full- to sixteenth-step Stepper Drivers operate from a single 36V supply and are available in an ultra-thin, compact package featuring a bottom side heat sink and adjacent pin short protection. A unique Ghost Supply Prevention function is also included that prevents malfunctions, along with voltage, current, and thermal protection for greater reliability.
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ROHM / LAPIS Semiconductor (Formerly OKI Semiconductor) Co-Develop a Dedicated Chipset for Intel® Atom™ Processor E6xx Series
ROHM and LAPIS Semiconductor (Formerly OKI Semiconductor) have developed a dedicated chipset for Intel®'s processor (the Atom™ E600 Series) consisting of a power management IC, clock generator IC, and input/output hub IC. It is a fully integrated System-on-a-Chip (SoC) solution utilizing the open standard PCI Express as the processor-to-chip interface, providing customers with the flexibility needed for a broad range of embedded applications.
Both companies have recently developed a reference board which includes a SATA, USB×2, audio, ethernet, and Micro-SD interface built-in, as well as a 5-inch LCD that is compatible with Linux OS (Fedora, v10), making evaluation possible by simply connecting to the peripheral circuitry. This development kit is available for purchase at Sophia Systems: Sophia Systems
Embedded Systems
As its name implies, embedded systems are microprocessor-based systems designed to control specific functions that are integrated within devices. The range of embedded systems spans to all aspects of modern life, from telecommunications systems and consumer electronics to transportation, medical, and automotive equipment. Virtually every electronic device manufactured today can be classified as an embedded system. In fact, it is estimated that of the billions of processors produced every year, less than 2% are used for the processors that go into PCs, Macs, and Unzix workstations. The overwhelming majority are implemented in devices to control only a few particular tasks – a key characteristic. This is in stark contrast to a general-purpose computer designed to perform a variety of functions.
Embedded systems offer several advantages over PC-type systems, including greater energy efficiency, security, and reliability. They are particularly suited for transportation, fire, safety, medical, and other life critical applications, since, they are often isolated from direct human intervention, providing better security. They also offer much greater reliability – there is often little to no margin for error so the software (firmware) is usually developed and tested more carefully than those for PCs and unreliable moving parts such as disk drives, switches, and buttons are avoided.
Embedded systems are controlled by one or more processing cores that are typically either microcontrollers or digital signal processors (DSPs). Microcontrollers are primarily used in interrupt-driven, control-oriented applications. They analyze input from switches, sensors, and other systems via software and output signals to actuators, relays, motors, and other driver systems. DSPs, on the other hand, are normally found in devices requiring fast processing of digitized analog signals. They are specifically designed to perform a large number of arithmetic operations repeatedly on a set of data in the smallest number of cycles. Although many standard microcontrollers can successfully execute DSP algorithms, they are often not suitable for smaller devices due to power and space constraints. DSPs, on the other hand, offer better performance, lower latency, lower costs, and require no specialized cooling or large batteries.
The versatility of embedded systems lends itself to countless uses, with new methods discovered every year in a variety of sectors. The dedicated nature provides several advantages, including lower overall costs and power consumption coupled with greater efficiency and performance. However, they do possess drawbacks. When problems develop on PCs the manufacturer can develop and release software patches or the hardware can be easily replaced. Problems with embedded systems, on the other hand, are often more difficult to fix, since they are not designed for human interaction and provide no easy method of updating their firmware or repairing hardware.
ECOMOS™ Series
Solutions in Handling Reduced Supply Voltages in Portables
ROHM's new ECOMOS™ series of n-channel and p-channel MOSFETs are designed to meet the prescribed operation at lower gate drive voltages that emerging generations of portable electronic devices require. ROHM's advanced proprietary processing has produced devices that exhibit RDS(ON) values as much as 90% lower than comparable devices when operated at ultra-low 1.5 V or 1.2 V gate drive (VGS) voltages. This improved electrical performance combined with ROHM's unique packaging design provides both high-efficiency, excellent power dissipation and small device footprint.
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Thin, High Brightness RGB LEDs: SMLW56 and SMLV56
ROHM offers two new RGB LEDs (smlw56rgb1w, smlv56rgb1w) featuring high brightness. Original package technology results in the thinnest form factor in the industry, making it possible to configure the LEDs a longer distance away from the object, resulting in uniform lighting and optimum color mixing.
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