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| 型号： | FAN7602BMX |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 9/17页 |
| 文件大小： | 0K |
| 描述： | IC PWM FLYBACK ISOLATED CM 8-SOP |
| 产品变化通告： | Mold Compound Change 12/Dec/2007 |
| 标准包装： | 1 |
| 输出隔离： | * |
| 频率范围： | * |
| 输入电压： | * |
| 输出电压： | * |
| 功率（瓦特）： | * |
| 工作温度： | * |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | * |
| 包装： | 标准包装 |
| 产品目录页面： | 1222 (CN2011-ZH PDF) |
| 其它名称： | FAN7602BMXDKR |
Applications Information
1. Start-up Circuit and Soft Start Block
The FAN7602B contains a start-up switch to reduce the
power loss of the external start-up circuit of the conven-
tional PWM converters. The internal start-up circuit
charges the V CC capacitor with 0.9mA current source if
the AC line is connected. The start-up switch is turned off
15ms after IC starts up, as shown in Figure 19. The soft-
start function starts when the V CC voltage reaches the
start threshold voltage of 12V and ends when the internal
soft-start voltage reaches 1V. The internal start-up circuit
starts charging the V CC capacitor again if the Vcc voltage
is lowered to the minimum operating voltage, 8V. The
UVLO block shuts down the output drive circuit and
some blocks to reduce the IC operating current and the
internal soft-start voltage drops to zero. If the V CC volt-
age reaches the start threshold voltage, the IC starts
switching again and the soft-start block works as well.
During the soft-start, the pulse-width modulated (PWM)
comparator compares the CS/FB pin voltage with the
soft-start voltage. The soft-start voltage starts from 0.5V
and the soft-start ends when it reaches 1V and the soft-
start time is 10ms. The start-up switch is turned off when
the soft-start voltage reaches 1.5V.
charging C F to adjust the offset voltage. If I FB is zero, C F
is discharged through R F and R S to lower offset voltage.
pin. The current-sense waveform is added to the offset
voltage, as shown in Figure 21. The CS/FB pin voltage is
compared with PWM + that is 1V - Plimit offset. If the CS/
FB voltage meets PWM+, the output drive is shut off. If
the feedback offset voltage is low, the switch on time is
increased. If the feedback offset voltage is high, the
switch on time is decreased. In this way, the duty cycle is
controlled according to the output load condition. In gen-
eral, the maximum output power increases as the input
voltage increases because the current slope during
switch on-time increases.
To limit the output power of the converter constantly, a
power-limit function is included. Sensing the converter
input voltage through the Latch/Plimit pin, the Plimit off-
the Plimit offset voltage is subtracted from 1V and the
switch on-time decreases as the Plimit offset voltage
increases. If the converter input voltage increases, the
switch on-time decreases, keeping the output power
constant. The offset voltage is proportional to the Latch/
Plimit pin voltage and the gain is 0.16; if the Latch/Plimit
12V
8V
V CC
voltage is 1V, the offset voltage is 0.16V.
Vcc
Start-up
Current
PWM
Plimit
Offset
1.5V
1V
0.5V
Soft Start
Voltage
Comparator
PWM+
Soft
Start
Power
Limit
3
R FB
CS/FB
I FB
R F
Isw
Soft Start
Time (10ms)
5ms
t
C F
R S
Figure 19. Start-up Current and V CC Voltage
Figure 20. Current-Sense and Feedback Circuits
2. Oscillator Block
The oscillator frequency is set internally. The switching
frequency is 65kHz.
1V
PWM+
CS/FB
Power Limit
Offset
FB
Offset
3. Current Sense and Feedback Block
The FAN7602B performs the current sensing for the cur-
rent-mode PWM and the output voltage feedback with
only one pin, pin3. To achieve the two functions with one
pin, an internal leading edge blanking (LEB) circuit to fil-
ter the current-sense noise is not included because the
external RC filter is necessary to add the output voltage
feedback information and the current-sense information.
Figure 20 shows the current-sense and feedback cir-
cuits. R S is the current-sense resistor to sense the switch
current. The current-sense information is filtered by an
GND
1V
PWM+
CS/FB
GND
On Time
(a) Low-Power Limit Offset Case
On Time
(b) High-Power Limit Offset Case
Power Limit
Offset
FB
Offset
RC filter composed of R F and C F . According to the output
voltage feedback information, I FB charges or stops
? 2007 Fairchild Semiconductor Corporation
FAN7602B Rev. 1.0.0
9
Figure 21. CS/FB Pin Voltage Waveforms
www.fairchildsemi.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| FAN7602BN | 功能描述:开关变换器、稳压器与控制器 GRN MODE PWM CNTRL RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
| FAN7602C | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:Green Current Mode PWM Controller |
| FAN7602CM | 功能描述:电流型 PWM 控制器 GREEN 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 |
| FAN7602CMX | 功能描述:电流型 PWM 控制器 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 |
| FAN7602CN | 功能描述:电流型 PWM 控制器 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 |
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