Date: /20/06

SP7653 Wide Input Voltage Range, .3MHz, Buck Regulator

© Copyright 2006 Sipex Corporation

4

Date: 2/17/06

SP7653 Wide Input Voltage Range, 1.3MHz, Buck Regulator

© Copyright 2006 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,

permits 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 startup, 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 cycle 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 operate properly. Other protection fea-

PIN DESCRIPTION

Pin #

Pin Name

Description

1-3

Ground connection for the synchronous rectifier

4,8,19-21

GND

Ground Pin. The control circuitry of the IC and lower power driver are

referenced to this pin. Return separately from other ground traces to the (-)

5

Feedback Voltage and Short Circuit Detection pin. It is the inverting input of

the Error Amplifier and serves as the output voltage feedback point for the

Buck Converter. The output voltage is sensed and can be adjusted through

an external resistor divider. Whenever V

reference, a short circuit fault is detected and the IC enters hiccup mode.

6

COMP

Output of the Error Amplifier. It is internally connected to the inverting input of

the PWM comparator. An optimal filter combination is chosen and connected

7

UVIN

to set minimum operating voltage.

9

SS

Soft Start. Connect an external capacitor between SS and GND to set the

soft start rate based on the 10µA source current. The SS pin is held low via a

1mA (min) current during all fault conditions.

10-13

Input connection to the high side N-channel MOSFET. Place a decoupling

capacitor between this pin and PGND.

14-16,23-26

LX

17

NC

No Connect

18

BST

High side driver supply pin. Connect BST to the external boost diode and

capacitor as shown in the Typical Application Circuit on page 1. High side

driver is connected between BST pin and SWN pin.

22

Vcc

Input for external 5V bias supply