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参数资料
| 型号： | SG6841SZ |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 9/14页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBACK PWM 8-SOIC |
| 产品变化通告： | Mold Compound Change 12/Dec/2007 |
| 标准包装： | 2,500 |
| PWM 型： | 控制器 |
| 输出数： | 1 |
| 频率 - 最大： | 70kHz |
| 占空比： | 90% |
| 电源电压： | 10 V ~ 20 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -20°C ~ 85°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
Product Specification
High-integrated Green-mode PWM Controller
OPERATION DESCRIPTION
Start-up current
Typical start-up current is only 30uA so that a high
resistance, and low-wattage, start-up resistor can be used
to minimize power loss. For an AC/DC adapter with
universal input range, a 1.5 M ? , 0.25W, start-up resistor
and a 10uF/25V VDD hold-up capacitor are enough for
this application.
Operating current
Operating current has been reduced to 3mA. The low
operating current enables a better efficiency and reduces
the requirement of VDD hold-up capacitance.
Green Mode Operation
The patented green-mode function provides an
off-time modulation to reduce the switching frequency in
the 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 will be linearly decreased to
the minimum green mode frequency around 10kHz (R i
=26k ? ).
Oscillator Operation
A resistor from RI pin to ground will generate a
constant current source for SG6841. This current is used
to charge an internal capacitor and hence the internal
clock and switching frequency are determined. Increase
the resistance will decrease the current source and reduce
the switching frequency. A 26k ? resistor R i creates a
50uA constant current I i and generates 65kHz switching
frequency. The relation between Ri and switching
freauency is:
SG6841
Current sensing and PWM current
limiting
Peak current mode control is utilized in SG6841 to
regulate output voltage and provide pulse by pulse current
limiting. The switch current is detected by a sense resistor
into the sense pin of SG6841. The PWM duty cycle is
determined by this current sense signal and V FB , the
feedback voltage. When the voltage on sense pin reaches
V COMP = (V FB –1.0)/3, a switch cycle will be terminated
immediately. V COMP is internally clamped to a variable
voltage around 0.85v for output power limit.
Leading Edge Blanking
Each time when the power MOSFET is switched on,
a turn-on spike will inevitably occur on the sense-resistor.
To avoid premature termination of the switching pulse, a
270 nsec leading-edge blanking time is built in.
Conventional RC filtering can therefore be omitted.
During this blanking period, the current-limit comparator
is disabled and it cannot switch off the gate driver.
Under-voltage lockout (UVLO)
The turn-on and turn-off threshold of SG6841 are
fixed internally at 16V/10V. During start-up, the hold-up
capacitor must be charged to 16V through the start-up
resistor so that SG6841 will be enabled. The hold-up
capacitor will continue to supply V DD before the energy
can be delivered from auxiliary winding of the main
transformer. V DD must not drop below 10V during this
start-up process. This UVLO hysteresis window insures
that hold-up capacitor is adequate to supply V DD during
start-up.
Gate Output / Soft Driving
The SG6841 BiCMOS output stage is a fast totem
pole gate driver. Cross conduction has been avoided to
f PWM =
1690
R I (k Ω )
( kHz ) ---------------------------- (1)
minimize heat dissipation, increases efficiency and
enhances reliability. The output driver is clamped by an
internal 18V Zener diode in order to protect power
The range of the PWM oscillation frequency is
designed as 50kHz ~ 90kHz.
MOSFET transistors against undesirable gate over
voltage. A soft driving waveform is implemented to
minimize EMI.
?System General Corp.
Version 2.1 (IRO33.0001.B5)
-9-
www.sg.com.tw
Jun.15,2006
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相关代理商/技术参数 |
参数描述 |
|---|---|
| SG6841SZ3 | 功能描述:电压模式 PWM 控制器 HI-INTEGRD GRN-MODE PWM CONTROLLER RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| SG6842BLVDZ | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| SG6842BLVSY | 功能描述:电流型 PWM 控制器 Current Mode 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 |
| SG6842BLVSZ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Fairchild Semiconductor Corporation 功能描述: |
| SG6842JLDZ | 制造商:Fairchild Semiconductor Corporation 功能描述: |
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