SGP400 Fairchild Semiconductor, SGP400 Datasheet - Page 9

• Manufacturer Part Number: SGP400
• Description: Low-Power Green-Mode PWM Flyback Power Controller without Secondary Feedback
• Manufacturer: Fairchild Semiconductor

Low-Power Green-Mode PWM Flyback Power Controller without Secondary Feedback
OPERATION DESCRIPTION
SGP400 devices integrate many useful functions for
low-power switch-mode power supplies. The following
descriptions highlight key features of the SGP400.
Start-up Current
The required start-up current is only 8µA, which allows a
high-resistance, low-wattage start-up resistor to be used
to
1.5MΩ/0.25W start-up 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 SGP400 can easily meet
international restrictions regarding standby power
consumption.
Constant Voltage (CV), Constant
Current (CC) without Feedback
The SGP400 can tightly regulate the output voltage and
provide
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 1.0.1 (IAO33.0084.B0)
supply
over-current
the
DD
hold-up capacitance. A 10µF/25V V
controller’s
protection
start-up
without
power.
requiring
A
DD
- 9 -
Over-Temperature Protection (OTP)
The SGP400 has a built-in temperature sensing circuit to
shut down PWM output if the junction temperature
exceeds 140°C. While PWM output is shut down, the
V
of the internal circuits are shut down and V
starts increasing again. When V
internal circuits, including the temperature sensing
circuit, start operating normally. If the junction
temperature is still higher than 140°C, the PWM
controller shuts down immediately. This situation
continues until the temperature drops below 110°C. The
PWM output is then turned back on. The temperature
hysteresis window for the OTP circuit is 30°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.
Leading-Edge Blanking
Each time the power MOSFET switches on, a spike
occurs 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 the blanking period, the current-limit
comparator is disabled and cannot switch off the
gate drive.
DD
DD
DD
voltage gradually drops to the UVLO voltage. Some
over-voltage clamping is built-in to prevent damage
Over-Voltage Clamping
www.sg.com.tw • www.fairchildsemi.com
Product Specification
DD
reaches 17V, all the
September 24, 2007
www.DataSheet4U.com
DD
exceeds 22.7V,
DD
SGP400
gradually