Fairchild SG6741SY, SG6741SZ, SG6741SY, SG6741SZ Schematic [ru]
SG6741
Highly Integrated Green-Mode PWM Controller
SG6741 — Highly Integrated Green-Mode PWM Controller
June 2011
Features
High-Voltage Startup
Low Operating Current: 4mA
Linearly Decreasing PWM Frequency to 22kHz
Frequency Hopping to Reduce EMI Emission
Peak-Current-Mode Control
Cycle-by-Cycle Current Limiting
Leading-Edge Blanking
Synchronized Slope Compensation
Gate Output Maximum Voltage Clamp: 18V
VDD Over-Voltage Protection (Auto Restart)
VDD Under-Voltage Lockout (UVLO)
Internal Open-Loop Protection
Constant Power Limit (Full AC Input Range)
Applications
General-purpose switch-mode power supplies and
flyback power converters, including:
Power Adapters
Open-Frame SMPS
Description
The highly integrated SG6741 PWM controller provides
several features to enhance the performance of flyback
converters.
The highly integrated SG6741 series of PWM
controllers provides several features to enhance the
performance of flyback converters.
To minimize standby power consumption, a proprietary
green-mode function provides off-time modulation to
linearly decrease the switching frequency at light-load
conditions. To avoid acoustic-noise problems, the
minimum PWM frequency is set above 22KHz. This
green-mode function enables the power supply to meet
international power conservation requirements. W ith the
internal high-voltage startup circuitry, the power loss
due to bleeding resistors is also eliminated. To further
reduce power consumption, SG6741 is manufactured
using the BiCMOS process, which allows an operating
current of only 4mA.
SG6741 integrates a frequency-hopping function that
helps reduce EMI emission of a power supply with
minimum line filters. Its built-in synchronized slope
compensation achieves stable peak-current-mode
control. The proprietary internal line compensation
ensures constant output power limit over a wide range
of AC input voltages, from 90V
SG6741 provides many protection functions. In addition
to cycle-by-cycle current limiting, the internal open-loop
protection circuit ensures safety when an open-loop or
output short-circuit failure occurs. PWM output is
disabled until V
then the controller starts again. As long as V
about 26V, the internal OVP circuit is triggered.
SG6741 is available in an 8-pin SOP package.
drops below the UVLO lower limit;
DD
to 264VAC.
AC
exceeds
DD
Ordering Information
Operating
Part Number
SG6741SZ -40 to +105°C 8-Lead Small Outline Package (SOP) Tape & Reel
SG6741SY -40 to +105°C 8-Lead Small Outline Package (SOP) Tape & Reel
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
SG6741 • Rev. 1.3.4 1
Temperature
Range
Package Packing Method
Application Diagram
SG6741 — Highly Integrated Green-Mode PWM Controller
Figure 1. Typical Application
Internal Block Diagram
Figure 2. Functional Block Diagram
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
SG6741 • Rev. 1.3.4 2
Marking Information
SG6741TP
XXXXXXXXYWWV
SG6741 — Highly Integrated Green-Mode PWM Controller
T: S = SOP
P: Z =Lead Free
Null=regular package
XXXXXXXX: Wafer Lot
Y: Year; WW: Week
V: Assembly Location
Marking for SG6741SZ
Marking for SG6741SY
Pin Configuration
ZXYTT
6741
TPM
GND
FB
NC
HV
F: Fairchild logo
Z: Plant code
X: 1 digit year code
Y: 1 digit week code
TT: 2 digits die run code
T: Package type (S = SOP)
P: Y=Green package
M: Manufacture flow code
Figure 3. Top Mark
GATE
VDD
SENSE
RI
Figure 4. Pin Configuration (Top View)
Pin Definitions
Pin # Name Description
1 GND Ground.
2 FB
3 NC No connection.
4 HV For startup, this pin is pulled high to the line input or bulk capacitor via resistors.
5 RI
6 SENSE
7 VDD
8 GATE The totem-pole output driver. Soft driving waveform is implemented for improved EMI.
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
SG6741 • Rev. 1.3.4 3
The signal from the external compensation circuit is fed into this pin. The PWM duty cycle is
determined in response to the signal on this pin and the current-sense signal on the SENSE pin.
A resistor connected from the RI pin to GND pin provides the SG6741 with a constant current
source. This determines the center PWM frequency. Increasing the resistance reduces PWM
frequency. Using a 26KΩ resistor (R
Current sense. The sensed voltage is used for peak-current-mode control and cycle-by-cycle
current limiting.
Power supply. The internal protection circuit disables PW M output as long as VDD exceeds the
OVP trigger point.
) results in a 65kHz center PWM frequency.
I
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