Product Specification
BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
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.
FEATURES
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384x series pin-to-pin compatible
Linearly decreasing PWM frequency
Burst-mode at low/zero load
5uA start-up current
5mA operating current
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.
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
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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
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
Green-mode Operation
Oscillator Frequency vs. COMP
From bridge rectifier
120~ 380VDC
From auxiliary winding
Oscillator Frequency (Fosc) vs COMP Voltage
CIN
RIN
60
10u
1.5M
50
40
30
20
10
0
VCC
R41
100
COMP
VREF
Rac
10k
OUTPUT
C21
0.1u
R42
1k
RT
SG384x
10k
SENSE
RS
C25
CT
3.3n
0.3
100p
VFB
1
1.5
2
2.5
3
GND
COMP VOLTAGE (V)
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
- 1 -
www.sg.com.tw
Jun.28,2004