[Technology Report]
Controller ICs Energize Power-Supply Design
New "do-it-yourself" controller and driver ICs give systems builders options to tackle the difficult task of providing power supplies for today's demanding equipment.
Two of the latest controller ICs to hit the market are International Rectifier's iP1201/1202 from the company's iPOWIR family. Called "Two-Phase dc-dc Power Blocks," the devices are synchronous buck converters intended for non-isolated POL applications (Fig. 2). Each can deliver a 30-A single output or two 15-A dual outputs at output voltages that span the low-voltage range requirements of many microprocessors, ASICs, and other high-performance digital devices in today's systems. The iP1201 provides outputs from 0.8 to 2.5 V with a 3.3-V input and 0.8 to 3.3 V for a 5-V input. The iP1202 covers 0.8 to 5 V for a 12-V input and 0.8 to 3.3 V for an input below 6 V.
According to Carl Smith, marketing manager for network and communications products, dc-dc sector, "If you try to lay out discrete devices and passives on a pc board, it becomes quite involved. With the iP1201/1202, you get guaranteed power losses which encompass all of the effects of switching and conduction losses, including the driver losses and second-order losses associated with the layout." This allows such controllers to operate at efficiencies of greater than 90%, an important consideration to limit dissipation in the power system.
"Whether you want to build or buy, we believe we have an appropriate solution," says Tony Armstrong, product marketing manager, Power Business Unit, Linear Technology Corp. The company offers a full array of power management products that run the gamut from a wide variety of switching regulators to hot-swap controllers to dc-dc converters to power controllers. "In particular," Armstrong notes, "the breadth of our PolyPhase products addresses numerous applications."
A pair of Maxim step-down buck controller ICs, the MAX5033/5035, includes an internal low-RDS(ON), high-voltage DMOS transistor to provide high efficiency and reduced system cost. "Putting the switches inside the controller IC gives you simplicity and cost savings and reduces layout problems," says Nitin Kalje, corporate applications engineer.
Built-in FETs are generally for lower-power applications up to around 3 A: The MAX5033 is rated for 500 mA of output current. The MAX5035 is a 1-A output controller. Both can handle inputs from 7.5 to 76 V and use just 350 mA of quiescent current at no-load conditions. Employing pulse-width modulation (PWM), the converters operate at a fixed 125-kHz switching frequency at heavy loads. However, they automatically switch to a pulse-skipping mode at light loads to reduce the quiescent current and improve efficiency. Both come in fixed output voltage (3.3, 5, and 12 V) and adjustable (1.25 to 13.2 V) output versions.
Analog Devices' entry for do-it-yourselfers is the ADP3050, a 200-kHz step-down switching-regulator controller that integrates a 1-A power switch and all of the control, logic, and protection functions necessary for standalone operation. The controller accepts input voltages from 3.6 to 30 V and offers two output options—adjustable and fixed at 3.3 and 5 V. A 2.5-V on-chip regulator provides the internal operating current to enhance efficiency. The internal compensation scheme allows the use of any type of output capacitor—tantalum, ceramic, or electrolytic—and equivalent-series-resistance (ESR) value. A complete regulator design requires only a few external components that can be standard off-the-shelf devices.
Control features include a shutdown input that puts the controller in a low-power mode, reducing the supply current to under 20 mA. Thermal shutdown and cycle-by-cycle current limiting for the power-switch supply complete device protection under fault conditions.
BIG-LOAD DRIVERS For high-current POL applications, a multiphase converter is needed, such as Fairchild Semiconductor's FAN5019, a two- to four-phase synchronous buck controller. "To get high current," explains Madhu Rayabhari, "you need multiple units of power conversion connected in parallel. Each unit is called a phase. To get 90-A capability, for example, you need a three-phase dc-dc converter with each phase supplying 30 A."
Such a three-phase arrangement uses the FAN5019 driving three FAN5009 synchronous dc-dc MOSFET drivers (Drill Deeper: See a schematic of this arrangement online at www.elecdesign.com.) Intended for powering high-current, low-voltage CPU cores, the circuit's output voltage ranges from 0.8375 to 1.6 V and can supply 74 A dc, 93 A peak. Because of the high current capability, all of the parts are individual components mounted on a pc board. In such high-current, multiphase applications, the drivers generate so much heat, they must be external to the controller and the MOSFETs.
One advantage of a multiphase design is that the output's ripple voltage rides at a much higher frequency than in a single-phase converter. For example, if each phase operates at 1 MHz, the ripple is around 3 MHz, and its magnitude is reduced. This makes it easier to filter, resulting in fewer and smaller filter components, lower component cost, reduced power consumption, and less area occupied on a pc board.
Please refresh the page if you have trouble reading this text.
Search Electronic Design
Email Newsletter
Sponsored By:
The Find Power Products monthly newsletter brings you the most important new developments within the world of power design. The newsletter includes exerpts from industry leader Sam Davis's exclusive blog, as well as overviews of the latest new products.
Enter Email to Subscribe
Web Seminar
Sponsored By:
Title: Exploring How Good GUIs Drive Adoption in the Digital Power Management Space
Reprints
