4

Rev F: /0/06

SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator

© Copyright 2006 Sipex Corporation

General Overview

The SP7652 is a fixed frequency, voltage

mode, synchronous PWM regulator opti-

mized for high efficiency. The part has been

designed to be especially attractive for split

plane applications utilizing 5V to power

the controller and 3V to 20V for step down

conversion.

The heart of the SP7652 is a wide bandwidth

transconductance amplifier designed to ac-

commodate Type II and Type III compensa-

tion schemes. A precision 0.8V reference,

present on the positive terminal of the error

amplifier, permits the programming of the

The output of the error amplifier, COMP,

which is compared to a .V 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 frequency to

600kHz.

THEORY OF OPERATION

The SP7652 contains two unique control

features that are very powerful in distributed

applications.First,asynchronousdrivercon-

trol is enabled during start up, to prohibit the

low side NFET from pulling down the output

until the high side NFET has attempted to

turn on. Second, a 100% duty cycle timeout

ensuresthatthelowsideNFETisperiodically

enhanced during extended periods at 100%

dutycycle.Thisguaranteesthesynchronized

refreshing of the BST capacitor during very

large duty cycle ratios.

The SP7652 also contains a number of

valuableprotectionfeatures.Programmable

value at which the conversion voltage can

safely begin down conversion, and an inter-

itselfhasenoughvoltagetooperateproperly.

Other protection features include thermal

shutdown and short-circuit detection. In the

event that either a thermal, short-circuit, or

PIN DESCRIPTION

Pin #

Pin Name

Description

-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

5

Feedback Voltage and Short Circuit Detection pin. 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 VFB drops 0.25V below the positive reference, a short circuit

fault is detected and the IC enters hiccup mode.

6

COMP

Output of the Error Amplifier. Internally connected to the inverting input of the

PWM comparator. An optimal filter combination is chosen and connected to this

pin and either ground or VFB to stabilize the voltage mode loop.

7

UVIN

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 0µA source current. The SS pin is held low via a mA

(min.) current during all fault conditions.

0-3

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

tor between this pin and PGND.

4-6,23-

26

LX

7

NC

No Connect.

8

BST

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

tor as shown in the Typical Application Circuit on page one. High-side driver is

connected between BST and SWN pin.

22

Input for external 5V bias supply.