9

Feb2-07 Rev O

SP7663 Wide Input Voltage Range 6A, 600kHz Buck Regulator

© 2007 Sipex Corporation

theamplifier’scurrentlimited(+/-150µA)

transconductance, there are many ways to

compensatethevoltagelooportocontrolthe

COMPpinexternally.Ifasimple,single-pole,

single-zero response is desired, then com-

pensation can be as simple as an RC circuit

toGround.Ifamorecomplexcompensation

isrequired,thentheamplifierhasenough

bandwidth(45°at4MHz),andenoughgain

(60dB)torunTypeIIIcompensationschemes

with adequate gain and phase margins at

crossover frequencies greater than 50kHz.

The common mode output of the error am-

plifieris0.9Vto2.2V.Therefore,thePWM

voltageramphasbeensetbetween.Vand

2.2V to ensure proper0% to 00% dutycycle

capability. The voltage loop also includes

two other very important features. One is a

nonsynchronousstartupmode.Basically,the

synchronousrectifiercannotturnonunless

the high side switch has attempted to turn

on or the SS pin has exceeded .7V. This

featurepreventsthecontrollerfrom“dragging

down” the output voltage during startup or

in fault modes.

GH

Voltage

GL

Voltage

V(VIN)

0V

-0V

-V(Diode) V

V(VIN)+V(VCC)

BST

Voltage

V(VCC)

TIME

SWN

Voltage

VBST

VSWN

V(VCC)

The second feature is a 00% duty cycle

timeout that ensures synchronized refresh-

ing of the BST capacitor at very high duty

ratios. In the event that the high side NFET

is on for 20 continuous clock cycles, a reset

isgiventothePWMflipflophalfwaythrough

cycle, in turn refreshing the BST capacitor.

The boost capacitor is used to generate a

high voltage drive supply for the high side

Power MOSFETs

TheSP7663containsapairofintegratedlow

resistance N-channel switches designed to

drive up to 6Aof output current. Care should

be taken to de-rate the output current based

on the thermal conditions in the system such

as ambient temperature, airflow and heat

sinking.Maximumoutputcurrentcouldbe

limited by thermal limitations of a particular

application by taking advantage of the inte-

grated-over-temperature protective scheme

employed in the SP7663. The SP7663 incor-

porates a built-in overtemperature protection

to prevent internal overheating.

Setting Output Voltages

The SP7663 can be set to different output

voltages. The relationship in the following

formula is based on a voltage divider from

set to an internal reference voltage of 0.80V.

Standard1%metalfilmresistorsofsurface

mount size 0603 are recommended.

R2 = R /

setting, simply remove R2 from the board.

Furthermore, one could select the value of

the R and R2 combination to meetthe exact

output voltage setting by restricting the R

resistance range such that 10KΩ < R1 <

100KΩforoverallsystemloopstability.

APPLICATIONS INFORMATION