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參數資料
| 型號： | FA3647 |
| 廠商： | FUJI ELECTRIC HOLDINGS CO., LTD. |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | PWM control IC with light load power saving function For Switching Power Supply Control |
| 中文描述： | 輕負載的PWM與節水開關電源控制功能電源控制IC |
| 文件頁數： | 9/21頁 |
| 文件大小： | 406K |
| 代理商： | FA3647 |
FA3641P(N), FA3647P(N)
66
Fig. 7 CS pin waveform
Fig. 6 CS pin circuit
4. CS pin circuit
As shown in Figure 6, capacitor Cs is connected to the CS pin.
The CS pin voltage varies depending on the charging voltage of
this capacitor Cs. When the power is turned on, the constant
current source (6.5
μ
A) begins to charge capacitor. Accordingly,
the CS pin voltage rises as shown in Figure 7. The CS pin
voltage is connected to the PWM comparator, which is
characterized to make output based on the lowest of input
voltages. The device enters soft-start mode while the CS pin
voltage is between 1.0V and 2.4V. During normal operation, the
CS pin is clamped at 4.0V by internal zener diode.
If the output voltage drops due to an overload and the FB
voltage rises to 3V or more, the clamp voltage 4.0V is canceled
and the CS pin voltage rises to 9.5V. The CS pin is also
connected to latch comparator C2. If the CS pin voltage rises
to 8.5V or more, comparator C2 toggles to turn off the 5V REF
circuit, thereby shutting the output down. Since the CS pin is
also connected to comparator C1, the 5V REF circuit can be
turned off to shut the output down by dropping the CS pin
voltage below 0.68V. In this way, comparator C1 can be used
for output on-off control.
As explained above, the CS pin can be used for soft-start,
overload output shutdown, and output on-off control by varying
the voltage.
Further details on the above three major functions of the CS pin
are given below.
4.1 Soft start function
Figure 8 shows the soft start circuit. Figure 9 is a soft-start
operation timing chart. The CS pin is connected to capacitor
Cs. When the power is turned on, the constant current source
(6.5
μ
A) begins to charge the capacitor. As shown in the timing
chart, the CS pin voltage rises slowly in accordance with the
capacitor Cs charging current. The CS pin is also connected to
the IC internal PWM comparator, which has such
characteristics that the voltage is determined to output on the
basis of the lowest of input voltages. The comparator output
pulse slowly widens to cause a soft start as shown in the timing
chart.
The soft start period can be approximately estimated by the
period t
S
, from the time the IC is activated to the time the output
pulse width widens to 30%. The period is given by the following
equation:
ts [ms] 250 Cs ...................................................... (3)
Cs : Soft start capacitor [
μ
F]
Fig. 8 Soft-sart circuit
Fig. 9 Soft-sart timing chart
相關PDF資料 |
PDF描述 |
|---|---|
| FA3647N | PWM control IC with light load power saving function For Switching Power Supply Control |
| FA3647P | PWM control IC with light load power saving function For Switching Power Supply Control |
| FA365 | THIN SMD HIGH-FREQUENCY CRYSTAL UNIT |
| FA-365 | THIN SMD HIGH-FREQUENCY CRYSTAL UNIT |
| FA3675F | For Switching Power Supply Control |
相關代理商/技術參數 |
參數描述 |
|---|---|
| FA3647N | 制造商:FUJI 制造商全稱:Fuji Electric 功能描述:PWM control IC with light load power saving function For Switching Power Supply Control |
| FA3647N-H1 | 制造商:Fuji Electric 功能描述: |
| FA3647P | 制造商:FUJI 制造商全稱:Fuji Electric 功能描述:PWM control IC with light load power saving function For Switching Power Supply Control |
| FA3647P-D1 | 制造商:Fuji Electric 功能描述: |
| FA365 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:THIN SMD HIGH-FREQUENCY CRYSTAL UNIT |
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