SP6137HCUSLASHTR datasheet(4/13 Pages) SIPEX

4 / 13 page

Date: 5/25/04

SP6137HV Dual Supply, Synchronous Buck Controller

General Overview

The SP6137HV 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 SP6137HV 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

down to 0.8V via the VFB pin. The output of the

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 SP6137HV contains two unique control

features that are very powerful in distributed

applications. 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 SP6137HV also contains a number of valu-

able protection features. A programmable input

(VIN) UVLO allows a user to set the exact value

at which the conversion voltage is at a safe point

to begin down conversion, and an internal VCC

UVLO ensures that the controller itself has

enough voltage to properly operate. Other pro-

1.7 V

COMPARATOR

ASYNC. STARTUP

0.4 V

FAULT

CLR

COUNT 20

CLOCK

PULSES

900 kHZ

CLK

CLOCK PULSE GENERATOR

GL HOLD OFF

100% Protection Logic

RESET

DOMINANT

QPWM

CLK

SYNCHRONOUS

DRIVER

GND

2 GL

PWM LOOP

5 COMP

POS REF

FAULT

0.8V

CORE

REFERENCE

FAULT

SOFTSTART INPUT

RAMP = 1.1V

VFBINT

VPOS

Gm ERROR AMPLIFIER

9 GH

8 SWN

10 BST

VFB

10 µA

VCC

FAULT

REF OK

FAULT

POWER FAULT

HICCUP FAULT

REF OK

VIN UVLO

VCC UVLO

2.50 VON

2.20 V OFF

UVIN

4.25 V ON

4.05 V OFF

VCC

REF OK

200ms Delay

COUNTER

CLR

CLK

SET

DOMINANT

THERMAL

SHUTDOWN

145 ˚C ON

135 ˚C OFF

SHORT CIRCUIT

DETECTION

VFBINT

+ -

VPOS

0.25 V

THERMAL AND SHORT CIRCUIT PROTECTION

UVLO COMPARATORS

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