5

Date: 2/16/06

SP6134 Dual Supply, Synchronous Buck Controller

© Copyright 2006 Sipex Corporation

General Overview

The SP6134 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 applications

utilizing 5V to power the controller and 3V to

12V for step down conversion.

The heart of the SP6134 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 SP6134 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 SP6134 also contains a number of valuable

UVLO allows a user to set the exact value at

which the conversion voltage is at a safe point to

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

+

-

+

-