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| 型号： | SG6742MRSY |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 9/13页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR PWM GREEN CM OVP 8SOP |
| 标准包装： | 1 |
| 输出隔离： | 隔离 |
| 频率范围： | 62kHz ~ 68kHz |
| 输入电压： | 10.5 V ~ 22 V |
| 输出电压： | 18V |
| 功率（瓦特）： | 400mW |
| 工作温度： | -40°C ~ 105°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOP |
| 包装： | 标准包装 |
| 产品目录页面： | 1222 (CN2011-ZH PDF) |
| 其它名称： | SG6742MRSYDKR |
Functional Description
Startup Current
For startup, the HV pin is connected to the line input or
bulk capacitor through an external diode and resistor,
R HV , (1N4007 / 100K ? recommended). Typical startup
current drawn from the HV pin is 2.3mA and charges
the hold-up capacitor through the diode and resistor.
When the V DD capacitor level reaches V DD-ON , the
startup current switches off. At this moment, the V DD
capacitor only supplies the SG6742ML/MR to keep the
V DD before the auxiliary winding of the main transformer
provides the operating current.
Operating Current
Operating current is around 2.7mA. The low operating
current enables better efficiency and reduces the
requirement of V DD hold-up capacitance.
Green-Mode Operation
The proprietary green-mode function provides off-time
modulation to reduce the switching frequency in light-
load and no-load conditions. The on time is limited for
better abnormal or brownout protection. V FB , which is
derived from the voltage feedback loop, is taken as the
reference. Once V FB is lower than the threshold voltage,
switching frequency is continuously decreased to the
minimum green-mode frequency of around 22KHz.
Current Sensing / PWM Current Limiting
Peak-current-mode control is utilized to regulate output
voltage and provide pulse-by-pulse current limiting. The
switch current is detected by a sense resistor into the
SENSE pin. The PWM duty cycle is determined by this
current-sense signal and V FB , the feedback voltage.
When the voltage on SENSE pin reaches around
V COMP =(V FB –0.6)/4, the switch cycle is terminated
immediately. V COMP is internally clamped to a variable
voltage around 0.85V for output power limit.
Leading-Edge Blanking (LEB)
Each time the power MOSFET is switched on, a turn-on
spike occurs on the sense-resistor. To avoid premature
termination of the switching pulse, a leading-edge
blanking time is built in. During this blanking period, the
current-limit comparator is disabled and cannot switch
off the gate driver.
Under-Voltage Lockout (UVLO)
The turn-on and turn-off thresholds are fixed internally
at 15.5V and 9.5V. During startup, the hold-up capacitor
must be charged to 15.5V through the startup resistor to
enable the IC. The hold-up capacitor continues to
supply V DD before the energy can be delivered from
auxiliary winding of the main transformer. V DD must not
drop below 9.5V during startup. This UVLO hysteresis
window ensures that hold-up capacitor is adequate to
supply V DD during startup.
? 2008 Fairchild Semiconductor Corporation
SG6742ML/MR ? Rev. 1.0.4
9
Gate Output / Soft Driving
The BiCMOS output stage is a fast totem-pole gate
driver. Cross conduction has been avoided to minimize
heat dissipation, increase efficiency, and enhance
reliability. The output driver is clamped by an internal
18V Zener diode to protect power MOSFET transistors
against undesirable gate over voltage. A soft driving
waveform is implemented to minimize EMI.
Soft-Start
For many applications, it is necessary to minimize the
inrush current at startup. The built-in 5ms soft-start
circuit significantly reduces the startup current spike
and output voltage overshoot.
Built-in Slope Compensation
The sensed voltage across the current-sense resistor is
used for peak-current-mode control and pulse-by-pulse
current limiting. Built-in slope compensation improves
stability and prevents sub-harmonic oscillation.
SG6742ML/MR inserts a synchronized, positive-going,
ramp at every switching cycle.
Constant Output Power Limit
When the SENSE voltage across sense resistor R S
reaches the threshold voltage, around 0.9V, the output
GATE drive is turned off after a small delay, t PD . This
delay introduces an additional current proportional to t PD
? V IN / L P . Since the delay is nearly constant regardless
of the input voltage V IN , higher input voltage results in a
larger additional current and the output power limit is
higher than under low input line voltage. To compensate
this variation for a wide AC input range, a sawtooth
power-limiter is designed to solve the unequal power-
limit problem. The power limiter is designed as a
positive ramp signal fed to the inverting input of the
OCP comparator. This results in a lower current limit at
high-line inputs than at low-line inputs.
V DD Over-Voltage Protection (OVP)
V DD over-voltage protection is built in to prevent
damage due to abnormal conditions. If the V DD voltage
is over the over-voltage protection voltage (V DD-OVP ) and
lasts for t D-VDDOVP , the PWM pulses are disabled until
the V DD voltage drops below the UVLO, then starts
again. Over-voltage conditions are usually caused by
open feedback loops.
Thermal Protection
An NTC thermistor, R NTC , in series with resistor R A , can
be connected from the RT pin to ground. A constant
current I RT is output from the RT pin. The voltage on the
RT pin can be expressed as V RT= I RT ? (R NTC + R A ),
where I RT is 100μA. At high ambient temperatures, R NTC
is smaller, such that V RT decreases. When V RT is less
than 1.05V (V RTTH1 ), the PWM turns off after 12ms
(t D-OTP1 ). If V RT is less than 0.7V (V RTTH2 ), PWM turns off
after 100μs (t D-OTP2 ).
www.fairchildsemi.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| SG6742SY | 功能描述:电流型 PWM 控制器 Highly Integrated Gr Mode PWM Contrl RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| SG6742SZ | 功能描述:电流型 PWM 控制器 Highly-Integrated Grn Mode PWM Cntrl RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| SG6742WMRSY | 功能描述:电流型 PWM 控制器 High Integ GreenMode PWM Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| SG68 | 制造商:Ametherm Inc 功能描述: |
| SG6840 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:HIGH INTEGRATED PWM CONTROLLER |
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