5

Rev: C Date: 2/3/04

SP6134H Dual Supply, Synchronous Buck Controller

© Copyright 2004 Sipex Corporation

General Overview

The SP6134H is a fixed frequency, voltage

mode, synchronous PWM controller optimized

for high efficiency. The part has been designed

to be especially attractive for split plane applica-

tions utilizing 5V to power the controller and 3V

to 12V for step down conversion.

The heart of the SP6134H 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 oscil-

lator that accurately sets the PWM frequency to

600kHz.

FUNCTIONAL DIAGRAM

THEORY OF OPERATION

The SP6134H 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

NFET from pulling down the output until the

high side NFET has attempted to turn on. Sec-

ond, a 100% duty cycle timeout ensures that the

low side NFET is periodically enhanced during

extended periods at 100% duty cycle. This guar-

antees the synchronized refreshing of the BST

capacitor during very large duty ratios.

The SP6134H also contains a number of valu-

able protection features. A programmable input

at which the conversion voltage is at a safe point

UVLO ensures that the controller itself has

enough voltage to properly operate. Other pro-

1.7 V

1.7 V

COMPARATOR

ASYNC. STARTUP

0.4 V

FAULT

CLR

COUNT 20

CLOCK

PULSES

600 kHZ

CLK

CLOCK PULSE GENERATOR

SS

GL HOLD OFF

100% Protection Logic

Q

R

S

RESET

DOMINANT

QPWM

CLK

SYNCHRONOUS

DRIVER

GND

3

2 GL

PWM LOOP

5 COMP

POS REF

FAULT

1

7

0.8V

CORE

REFERENCE

V

CC

FAULT

SOFTSTART INPUT

RAMP = 1.1V

VFBINT

VPOS

Gm

Gm ERROR AMPLIFIER

9 GH

8 SWN

10 BST

VFB

SS

10 µA

VCC

VCC

VCC

FAULT

REF OK

FAULT

POWER FAULT

HICCUP FAULT

REF OK

VIN UVLO

VCC UVLO

2.50 VON

2.20 V OFF

6

UVIN

4.25 V ON

4.05 V OFF

Q

VCC

REF OK

200ms Delay

COUNTER

CLR

CLK

R

SET

DOMINANT

S

+

-

THERMAL

SHUTDOWN

145 ˚C ON

135 ˚C OFF

SHORT CIRCUIT

DETECTION

VFBINT

+ -

VPOS

0.25 V

THERMAL AND SHORT CIRCUIT PROTECTION

UVLO COMPARATORS

+

-

+

-