SG6849-100D ETC2 [List of Unclassifed Manufacturers], SG6849-100D Datasheet - Page 9

• Manufacturer Part Number: SG6849-100D
• Description: Low-Power Green-Mode PWM Flyback Power Controller without Secondary Feedback
• Manufacturer: ETC2 [List of Unclassifed Manufacturers]

Low-Power Green-Mode PWM Flyback Power Controller without Secondary Feedback
OPERATION DESCRIPTION
SG6849 devices integrate many useful functions for low
power switch mode power supplies. The following
descriptions highlight the key features of the SG6849.
Startup Current
The required startup current is only 5uA. This allows a
high-resistance, low-wattage startup resistor to be used to
supply the controller’s startup power. A 1.5 MΩ/0.25W
startup resistor can be used over a wide input range
(100V-240V AC) with very little power loss.
Operating Current
The operating current is normally 3.6mA. The low
operating current results in higher efficiency and reduces
the required V
hold-up capacitor can be used over a wide input range
(100V-240V AC) with very little power loss.
Green Mode Operation
The proprietary green-mode function provides off-time
modulation to linearly decrease the switching frequency
under light-load and zero-load conditions. The on-time is
limited to provide better protection against brownouts and
other abnormal conditions.
This green-mode function dramatically reduces power
consumption under light-load and zero-load conditions.
Power supplies using the SG6849 can easily meet
international
power-consumption.
Constant Voltage (CV) and Constant
Current (CC) without Feedback
The SG6849 can tightly regulate the output voltage and
provide over current protection without requiring
secondary-side feedback signals. For improved CV and
CC accuracy, the transformer leakage inductance should
be reduced as much as possible.
© System General Corp.
Version 1.0(IRO33.0002.B3)
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hold-up capacitance. A 10uF/25V V
restrictions
regarding
standby
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- 9 -
Over Temperature Protection (OTP)
The SG6849 has a built-in temperature sensing circuit to
shut down PWM output once the junction temperature
exceeds 150°C. While PWM output is shut down, the V
voltage will gradually drop to the UVLO voltage. Some of
the SG6849’s internal circuits will be shut down, and V
will gradually start increasing again. When V
17V, all the internal circuits, including the temperature
sensing circuit, will start operating normally. If the
junction temperature is still higher than 150°C, the PWM
controller will be shut down immediately. This situation
will continue until the temperature drops below 130°C.
The PWM output will then be turned back on. The
temperature hysteresis window for the OTP circuit is
20°C.
V
V
from over-voltage conditions. When V
PWM output is shut down. Over-voltage conditions may
be caused by an open photo-coupler loop or a short circuit
in the output.
Oscillator Operation
The oscillation frequency is fixed at 65kHz for the
SG6849-65, and at 100kHz for the SG6849-100.
Leading Edge Blanking
Each time the power MOSFET is switched on, a turn-on
spike will inevitably occur at the sense-resistor. To avoid
premature termination of the switching pulse, a 310ns
leading-edge blanking time is built in. Conventional RC
filtering is not necessary. During this blanking period, the
current-limit comparator is disabled, and it cannot switch
off the gate drive.
Constant Output Power Limit
When the SENSE voltage across the sense resistor R
reaches the threshold voltage (around 1.0V), the output
GATE drive will be turned off following a small
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over voltage clamping is built in to prevent damage
Over Voltage Clamping
Product Specification
www.sg.com.tw
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exceeds 22.7V,
Dec.29, 2003
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SG6849
reaches
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S