4

Date: 03/25/05

SP7653 Wide Input Voltage Range, 1.3MHz, Buck Regulator

© Copyright 2005 Sipex Corporation

General Overview

The SP7653 is a fixed frequency, voltage mode,

synchronous PWM regulator optimized for high

efficiency. The part has been designed to be

especially attractive for high input voltages of

2.5V to 20V.

The heart of the SP7653 is a wide bandwidth

transconductance amplifier designed to accom-

modate Type II and Type III compensation

schemes. A precision 0.8V reference, present on

the positive terminal of the error amplifier per-

mits the programming of the output voltage

error amplifier, COMP, compared to a 1.1V

peak-to-peak ramp is responsible for trailing

edge PWM control. This voltage ramp, and

PWM control logic are governed by the internal

oscillator that accurately sets the PWM fre-

quency to 1.3MHz.

THEORY OF OPERATION

The SP7653 contains two unique control fea-

tures that are very powerful in distributed appli-

cations. First, asynchronous driver control is

enabled during start up, to prohibit the low side

switch from pulling down the output until the

high side switch has attempted to turn on. Sec-

ond, a 100% duty cycle timeout ensures that the

low side switch is periodically enhanced during

extended periods at 100% duty cycle. This guar-

antees the synchronized refreshing of the Boost

capacitor during very large duty ratios.

The SP7653 also contains a number of valuable

allows the user to set the exact value at which the

conversion voltage can safely begin down con-

sures that the controller itself has enough volt-

age to properly operate. Other protection fea-

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