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参数资料
| 型号： | SG6846BCSZ |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 11/15页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR PWM PROG OVP OTP 8SOP |
| 标准包装： | 2,500 |
| 输出隔离： | 隔离 |
| 频率范围： | 44.8 ~ 136kHz |
| 输入电压： | 10.5 V ~ 30 V |
| 输出电压： | 18V |
| 功率（瓦特）： | 400mW |
| 工作温度： | -40°C ~ 150°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOICN |
| 包装： | 带卷 (TR) |
Operation Description
Startup Operation
The turn-on/turn-off thresholds are fixed internally at
f PWM (kHz) =
1690
R I (k Ω )
(2)
16.5V and 10.5V. To enable the SG6846B during
startup, the hold-up capacitor must first be charged to
16.5V through the startup resistor.
If an open-circuit or short-circuit to ground occurs at the
RI pin, the internal protection circuit immediately shuts
down the controller.
The hold-up capacitor continues to supply V DD before
energy can be delivered from the auxiliary winding of
the main transformer. The V DD must not drop below
10.5V during this startup process. This UVLO hysteresis
window ensures that the hold-up capacitor can
adequately supply V DD during startup.
The typical startup current is only 8μA, which allows a
high-resistance, low-wattage startup resistor to be used.
For constant output power limit over a universal input-
voltage range, the peak-current threshold is adjusted by
the voltage of the VIN pin. Since the VIN pin is
connected to the rectified AC input line voltage through
the resistive divider, a higher line voltage generates a
higher V IN voltage. The threshold voltage decreases as
the V IN increases, making the maximum output power at
high line input voltage equal to that at low line input.
The value of R-C network should not be so large it
affects the power limit (shown in Figure 19). R and C
should put on less than 300 ? and 1000pF, respectively,
to minimize power loss. A 1.5M ? /0.25W startup resistor
and a 10μF/25V V DD hold-up capacitor are sufficient for
a universal input range.
The required operating current has been reduced to
3.7mA, which enables higher efficiency and reduces the
V DD hold-up capacitance requirement.
Green-Mode Operation
The proprietary green-mode function provides off-time
modulation to continuously decrease the switching
frequency under light-load conditions. Maximum on-time
is limited to provide protection against abnormal
conditions. To further reduce power consumption under
zero-load condition, the PWM oscillator is completely
turned off and the power supply enters burst-mode.
Green mode dramatically reduces power consumption
under light-load and zero-load conditions. Power
supplies using SG6846B can meet restrictive
international regulations regarding standby power
consumption.
Oscillator Operation
A resistor connected from the RI pin to GND generates
a internal reference current source used to determine
the PWM frequency. Increasing the resistance
decreases the amplitude of the current source and
reduces the PWM frequency. Using a 26k Ω resistor
results in a corresponding 65kHz switching frequency.
If an open-circuit or short-circuit to ground occurs at the
RI pin, the internal protection circuit immediately shuts
down the controller.
Two-level Over-current Protection (OCP)
The cycle-by-cycle current limiting shuts down the PWM
immediately when the switching current is over the
peak-current threshold. Additionally, when the switching
current is higher than over-current threshold, the internal
counter counts down. When the total accumulated
counting time is more than ~200ms (R I = 26k ? ), the
controller is latched off and the internal counter counts
up. When the switching current is lower than over-
current threshold, the internal counter counts down.
When the total accumulated counting time is more than
~200ms (R I = 26k ? ), the controller is latched off.
This two-level OCP protection and up/down counter are
especially designed for SMPS with surge current output,
such as those for printers, scanners, and motor drivers.
Constant Output Power Limit
For constant output power limit over universal input-
voltage range, the peak-current threshold is adjusted by
the voltage of the VIN pin. Since the VIN pin is
connected to the rectified AC input line voltage through
the resistive divider, a higher line voltage generates a
higher V IN voltage. The threshold voltage decreases as
V IN increases, making the maximum output power at
high-line input voltage equal to that at low-line input.
Brownout Protection
Since the VIN pin is connected through a resistive
divider to the rectified AC input line voltage, it can also
be used for brownout protection. If the V IN voltage is
less than 0.7V, the PWM output is shut off. If the V IN is
over 0.9V, the PWM output is turned on again. The
hysteresis window for on/off is ~0.2V.
V DD Over-voltage Protection (OVP)
V DD over-voltage protection is built in to prevent
damage. If V DD is over 24V, SG6846B is latched off.
Over-Temperature Protection (OTP)
An external NTC thermistor can be connected from the
RT pin to GND. The impedance of the NTC decreases
at high temperatures. When the voltage of the RT pin
drops below 1.05V, the SG6846B is turned off. For
protection-mode options, see Ordering Information.
The relationship between R I
frequency is:
? 2008 Fairchild Semiconductor Corporation
SG6846B ? Rev. 1.3.4
and the switching
11
www.fairchildsemi.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| SG6846BLSY | 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 |
| SG6846BLSZ | 功能描述:电流型 PWM 控制器 Highly-Integrated Green-Mode PWM 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 |
| SG6846C | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
| SG6846CD | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Highly-Integrated Green-Mode PWM Controller |
| SG6846CDSMC_DBB14 WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
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