Document
SG6741A — Highly Integrated Green-Mode PWM Controller
April 2008
SG6741A — Highly Integrated Green-Mode PWM Controller
Features
High-voltage Startup Low Operating Current: 4mA Linearly Decreasing PWM Frequency to 18kHz Frequency Hopping to Reduce EMI Emissions Peak-current-mode Control Cycle-by-cycle Current Limiting Leading-edge Blanking (LEB) 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)
Description
The highly integrated SG6741A 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 18KHz. This green-mode function enables the power supply to meet international power conservation requirements. With the internal high-voltage startup circuitry, the power loss due to bleeding resistors is eliminated. To further reduce power consumption, SG6741A is manufactured using the BiCMOS process, which allows an operating current of only 4mA. SG6741A integrates a frequency-hopping function internally to reduce EMI emission of a power supply with minimum line filters. A built-in synchronized slope compensation achieves stable peak-current-mode control. The proprietary internal line compensation ensures constant output power limit over a wide AC input voltages, from 90VAC to 264VAC. SG6741A 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 VDD drops below the UVLO lower limit, when the controller starts up again. As long as VDD exceeds ~26V, the internal OVP circuit is triggered. SG6741A is available in an 8-pin SOP package.
Applications
General-purpose www.DataSheet4U.com switch-mode power supplies and flyback power converters, including:
Power Adapters Open-Frame SMPS
Ordering Information
Part Number
SG6741ASZ
Operating Temperature Range
-20 to +85°C
Package
8-Lead Small Outline Package (SOP)
Packing Method
Tape and Reel
All packages are lead free per JEDEC: J-STD-020B standard.
© 2008 Fairchild Semiconductor Corporation SG6741A • Rev. 1.0.0
www.fairchildsemi.com
SG6741A — Highly Integrated Green-Mode PWM Controller
Application Diagram
Figure 1. Typical Application
Block Diagram
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Figure 2. Block Diagram
© 2008 Fairchild Semiconductor Corporation SG6741A • Rev. 1.0.0
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SG6741A — Highly Integrated Green-Mode PWM Controller
Marking Information
T: S = SOP P: Z =Lead Free Null=regular package XXXXXXXX: Wafer Lot Y: Year; WW: Week V: Assembly Location
SG6741ATP XXXXXXXXYWWV
Figure 3. Top Mark
Pin Configuration
GND FB NC HV GATE VDD SENSE
RI
Figure 4. Pin Configuration
www.DataSheet4U.com Pin Definitions
Pin #
1 2 3 4
Name
GND FB NC HV
Description
Ground. Feedback. 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 SENSE pin. No Connection. Start-up Input. For start-up, this pin is pulled HIGH to the line input or bulk capacitor via resistors. Reference Setting. A resistor connected from the RI pin to GND pin provides a constant current source, which determines the center PWM frequency. Increasing the resistance reduces PWM frequency. Using a 26KΩ resistor for RI results in a 65kHz center PWM frequency. 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 PWM output as long as VDD exceeds the OVP trigger point. Driver Output. The totem-pole output driver. Soft driving waveform is implemented for improved EMI.
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5
RI
6 7 8
SENSE VDD GATE
© 2008 Fairchild Semiconductor Corporation SG6741A • Rev. 1.0.0
SG6741A — Highly Integrated Green-Mode PWM Controller
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. All voltage values, except differential voltages, are given with respect to the ground pin.
Symbol
VDD VHV VL PD ΘJA TJ TSTG TL ESD Supply Voltage
Parameter
Input Voltage to HV Pin Input Voltage to FB, SENSE, Pin Power Dissipation, TA < 50°C Thermal Resistance (Junction-to Air) Op.