SG3843G Ver la hoja de datos (PDF) - Unspecified

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SG3843G

BiCMOS Green-Mode PWM Controllers

Unspecified 

BiCMOS Green-Mode PWM Controllers

Product Specification

SG3842G/ SG3843G

FEATURES

384x series pin-to-pin compatible

Linearly decreasing PWM frequency

Burst-mode at low/zero load

5uA start-up current

5mA operating current

Vcc over voltage protection

Cycle-by-cycle current limiting

Zero cross-conduction

Slew rate controlled high current totem pole output

Fast current sense propagation delay

Under voltage lockout (UVLO) with hysteresis

APPLICATIONS

Switching mode power supplies

Power converters

DESCRIPTION

The SG348xG series of current-mode PWM

controllers combines high performance with Green-mode

power saving features. SG348xG controllers are fully

pin-to-pin compatible with bipolar UC384x devices, but

they have improved features and functionality. SG384xG

series controllers are compatible with the BiCMOS

fabrication process, enabling the use of low start-up

current and operating currents. This feature further

improves power conversion efficiency. The minimal

start-up current has been reduced to 5uA, and the

minimum operating current has been reduced to 5mA.

Each SG384xG has a slew rate controlled high current

totem pole output, ideally suited for driving a power

MOSFET while keeping EMI low.

The current-sense propagation delay is typically

50ns, resulting in significantly more effective constant

power protection. During normal operation, a SG384xG

controller acts as a fixed frequency PWM controller. The

PWM frequency can be easily programmed by changing

external RT and CT values. The SG384xG includes two

Green-mode functions that dramatically reduce power

usage, helping the power supply comply with the latest

international power saving guidelines. To cut power

consumption under light load conditions, the controller’s

Green-mode function will linearly decrease the PWM

frequency in response to decreases in the output load.

Under ultra light-load/zero-load conditions, the RT/CT

PWM oscillator periodically shuts down, and enters into

Burst-mode. This causes the IC’s supply voltage to begin

gradually dropping. Just before the supply voltage drops

below the UVLO voltage threshold, the RT/CT PWM

oscillator turns back on, to prevent the supply voltage

from going below the UVLO voltage.

SG384xG controllers also come with Over Voltage

Protection (OVP). This shuts down PWM output if the

supply voltage ever exceeds 27V. The SG384xG series

comes in 8-pin DIP and SOP packages.

TYPICAL APPLICATION

From bridge rectifier

120~ 380VDC

RIN

1.5M

VCC

COMP

Rac

OUTPUT

10k

VREF

C21

RT

0.1u SG384x

10k

SENSE

CT

RT/CT

3.3n

VFB

GND

From auxiliary winding

CIN

10u

R41

100

R42

1k

C25 RS

100p 0.3

Green-mode Operation

Oscillator Frequency vs. COMP

Oscillator Frequency (Fosc) vs COMP Voltage

60

50

40

30

20

10

0

1

1.5

2

2.5

3

COMP VOLTAGE (V)

© System General Corp.

-1-

Version 1.4 ( IRO33.0007.B3)

www.sg.com.tw

Jun.28,2004

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