While lacking the glitz of so-called digitally-based systems (search www.eeProductCenter.com for article ID:163105176), traditional PWM-based controller ICs for today’s switching power supplies show a fair amount of innovation in their own right. A snapshot of the most recent products for the basic datacom, telecom, and portable areas shows activity split along two lines: Controllers suited for extending the functionality of the typical AC/DC supply, versus those for both general purpose and specialized DC/DC converters. Despite an advanced level of chip integration and performance unheard of just a few years ago, vendors hone in on three timeless and somewhat related themes: even lower (external) parts count, more efficient operation, and higher accuracy.
Taking integration to the limit at the supply’s front-end, ON Semiconductor’s (Phoenix) NCP1603 is a combination power-factor-correction and pulse-width-modulation (PFC/PWM) controller (search www.eeProductCenter.com for article ID:168601557). The integrated solution, versus separate PWM and PFC controllers, is designed to save up to 10 components for powering notebooks and LCDs.
Another chip widely associated with the front-end and AC/DC applications, the ASM8P18xx from Alliance Semiconductor (Santa Clara, Calif.), employs user-configurable spread spectrum modulation circuitry to reduce electromagnetic interference (search www.eeProductCenter.com for article ID:165701671). Billed as the industry’s first such PWM controller with EMI reduction, it delivers up to 1 amp for AC/DC and DC/AC (inverter) applications.
With the focus on saving power at every opportunity, National Semiconductor’s (Santa Clara, Calif.) LM5021 is suited to single-ended flyback and forward AC/DC converters for telecom, networking, and industrial and consumer power supplies (search eeProductCenter.com for article ID: 163702831). This chip, which integrates a high-frequency, current-mode topology (most typically used, generally applied to simplify loop compensation and improve transient response), includes skip-, burst-, and low-power bias circuitry to improve efficiency over a wide load range.
Equally at home in AC/DC or DC/DC applications, National’s LM5026 PWM controller is promoted as the industry’s most advanced type for forward converter topologies using an active-clamp/reset design (search www.eeProductCenter.com for article ID: 172300881). The 100-V device is designed to simplify loop compensation and reduce parts count while boosting overall efficiency compared to standard forward converters. The active-clamp technique allows operation at duty cycles greater than 50 percent to deliver a regulated output from supplies whose input voltage varies widely. Three versions are available: The single-channel current-mode LM5026, voltage-mode LM5025, and the dual-channel current-mode LM5034.
New DC/DC directions
Other flyback entries include Linear Technology’s (Milpitas, Calif.) LT3825, a synchronous DC/DC controller for isolated power supplies in telecom, medical, industrial, and instrumentation systems (search www.eeProductCenter.com for article ID: 175002526). The company, focusing their efforts on the growing 10-60 watt power supply area, touts this part for its superior thermal performance at high output currents. It also reportedly brings a 3 to 5 percent increase in power supply efficiency, and a much simpler approach compared to forward converters applied in a lower power design.
Also focusing in on tighter board installations, International Rectifier’s (El Segundo, Calif.) IR3094 is a three-phase PWM control IC with integrated drivers suited for 80-amp POL converters (nominal 12-volt input). The chip, with the company’s DirectFET MOSFET output stages, cuts parts count (from 13 to 7) and real-estate requirements by up to 40 percent (search www.eeProductCenter.com for article ID:174915046). In absolute terms, this solution occupies less than 2 square inches. Also in the high-accuracy stakes, International Rectifier offers its IR3637SPbF and IR3637ASPbF, which touts 1 percent accuracy for POL designs suited for powering DDR memory, FPGAs, and video graphics processors (search www.eeProductCenter.com for article ID: 171204032). The 400 kHz IR3637SPbF, working from a nominal 12-volt input, is designed for 15-amp applications. The 600 kHz IR3637APbF is suited for 7-amp applications and reportedly provides increased control loop bandwidth for improved transient response.
Multiphase controllers for high-accuracy applications also continue to advance. Intersil’s (Milpitas, Calif.) two-phase ISL6310 and three-phase ISL6308 are promoted as providing high accuracy of the kind typically reserved for processor core applications (search www.eeProducCenter.com for article ID: 168602104). Designed for (non-core) server and embedded system peripherals, they provide ±0.8 percent system accuracy over temperature for the 0.6- and 0.9-volt versions, and ±0.5 percent for the 1.2 and 1.5 volt versions. Users set output voltage using an on-chip DAC (two-bit code) or an external reference for 0.6, 0.9, 1.2, or 1.5 volts. These devices can be operated at up to 1.5 MHz per phase. The device’s on chip drivers (for external MOSFETs) can be programmed to deliver a 5 to 12 volt output to secure the optimum trade-off between switching and conduction losses associated with the upper and lower MOSFETs.
Other entries include Intersil’s ISL6232, a quad-output supply IC for notebook computers (search eeProductCenter.com for article ID: 166400939). The chip comprises two PWM controllers that each provide 0.8 to 5.5 volts or fixed 3.3 and 5-volt outputs. Another chip, the company’s ISL6440, is a dual PWM controller IC that’s optimized for converting wall adapter or intermediate bus inputs (4.5-24 volts) to the low-voltage output (down to 0.8 volts) required for a wide variety of telecom, datacom, and consumer products (search www.eeProductCenter.com for article ID: 160401189). Similarly, Maxim’s (Sunnyvale, Calif.) MAX8717 is a dual PWM controller for notebook computers and battery-powered equipment.
Focusing on micropower applications, Linear Technology’s (Milpitas, Calif.) LTC3827 two phase controller draws just 115 microamps, or 80 microamps when one channel is active (search eeProductCenter.com for article ID:175002508). It’s the first controller to break the 100 microamp barrier, according to the company. It’s particularly suited to supplies that power audio systems, tuners, and CD/DVD players in automotive applications.
Power to the core
Moving deeper into the high-accuracy stakes, i.e., voltage regulator modules (VRMs), Intersil says its ISL6316 is the industry’s most accurate multiphase core controller for maintaining a tightly regulated output voltage versus load current and temperature (search www.eeProductCenter.com for article ID: 170703044). This controller, which drives up to four synchronized buck regulator channels for VR10.x and EVRD10.x systems, is reportedly the only such controller with tracking over-current protection based on a single, external negative temperature coefficient thermistor. Another entry, Maxim’s MAX8760, is a dual-phase controller in the company’s Quick-PWM series for AMD 9G and AMD Hammer CPU core supplies.