PWM Controller Enables Digital Control

Sep 1, 2004 12:00 PM
By David Morrison, Editor, Power Electronics Technology

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A pulse width modulator (PWM) controller from Microchip Technology allows the introduction of digital control into analog power-supply designs while providing high-speed PWM operation. Designed for use with a microcontroller, the MCP1630 PWM enables precision control, digital communications and programmability for initial settings or on-the-fly adjustment or calibration. The chip's fast operation is indicated by a current sense-to-output delay of 12 ns typ. or 25 ns max. In contrast, comparable existing devices may specify delays that are two or more times that of the Microchip part.

The chip consists of a high-speed comparator with a high-performance error amplifier and a PWM latch to perform the analog PWM function. The controller allows an external microcontroller to adjust output voltage or current, switching frequency, maximum duty cycle and other features. Capable of supporting all switched-mode power-supply topologies, the MCP1630 is best suited to applications requiring medium to high levels of intelligence and operation at frequencies ranging from 200 kHz to 1 MHz. Typical applications include battery chargers for Li-ion and NiMH chemistries, intelligent power systems, isolated dc-dc converters (bricks), ac power factor correction, multi-output supplies and multiphase supplies (see the figure).

With its MCU-adaptable features, the MCP1630 is designed to overcome the limitations of existing components developed for digital power-supply control. Some past solutions for digital control have involved piecing together analog PWMs, logic circuits and specialty analog circuits. Although other products have provided integrated off-the-shelf solutions, some of these may have limited flexibility or feature sets.

The short-current sense-to-output delay of the MCP1630 enables tight control of the maximum switch current over a wide range of input voltages. This fast operation reflects the speed of the PWM controller's internal comparator, which, as might be expected, is obtained with some tradeoff in the device's operating current. However, it's difficult to make direct comparisons between the 2.8-mA typ. I_q of the MCP1630 and the I_q values of comparable devices from other vendors because of variations in functionality among the similar devices.

The MCP1630 also integrates protection features, such as undervoltage lockout, output short circuit and overtemperature protection. Other specifications include rise and fall times of 5.9 ns and 6.2 ns, respectively, and a peak-current limit of ±5%.

To aid product development using the MCP1630, Microchip is offering a battery charger demo board that implements a SEPIC-style constant-current converter. Available now in an 8-pin MSOP, the chip is priced at $0.98 each in quantities of 1000. For more information, visit www.microchip.com/mcp1630.

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