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參數資料
型號: FA3647P
廠商: FUJI ELECTRIC CO LTD
元件分類: 穩壓器
英文描述: PWM control IC with light load power saving function For Switching Power Supply Control
中文描述: 1 A SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDIP8
封裝: DIP-8
文件頁數: 12/21頁
文件大小: 406K
代理商: FA3647P
FA3641P(N), FA3647P(N)
69
Fig. 18 Oscillator circuit
7. Undervoltage lockout circuit (U.V.L.O.)
The IC incorporates a circuit that prevents the IC from
malfunctioning when the supply voltage drops. When the
supply voltage is raised from 0V, the IC starts operation with
Vcc = 16.5V (typ). If the supply voltage drops, the output is
shut down when Vcc = 9.0V (typ). When the undervoltage
lockout circuit operates, the outputs of the OUT and CS pins go
low to reset the IC.
8. Output circuit
The IC contains a push-pull output stage and can directly drive
the MOSFET. The maximum peak current of the output stage is
a sink current of 1A and a source current of 0.5A. If the circuit
operation stops when the undervoltage lockout circuit operates,
the OUT pin voltage goes low to shut down the MOSFET.
I
Design advice
1. Externally setting the oscillation frequency in the light-
load mode
As explained in item 2 in
Description of each circuit,
the IC has
a function that automatically lowers the oscillation frequency
when the load is light, to reduce the loss of the power supply in
standby mode. The oscillation frequency goes down to about
46% without adjustment by external circuit.
To further lower the frequency to below 46%, connect
adjustment resistor Rr between the RT and REF pins as shown
in Figure 18. Then the fixed frequency determined by Rt also
falls. The relationship between the external resistance and
oscillation frequency is outlined below:
............................ (5)
....... (6)
f
O
: Fixed frequency [kHz]
fr: Minimum frequency in variable mode [kHz]
Rt: Timing resistance [k
]
Rr:Adjustment resistance [k
]
A =
f
0
4880
1.4f
0
Select Rt and Rr so that the relationship between the two
satisfies the following:
Rt < 0.3 Rr .................................................................... (7)
Set the minimum frequency in light-load mode to 10 kHz or
more.
Failure to keep the above relationship may disturb the
operation.
Note that the above expressions determine approximate values.
Note also that the minimum frequency in light-load mode
depends on such conditions as the power supply efficiency.
Therefore, check the operation using a practical circuit to make
a final decision.
Calculation example
To set the fixed frequency f
O
= 100kHz and minimum frequency
in light-load mode to fr = 20kHz, the following can be obtained
from expressions (5).
Rt 37.7 [k
]
Decrease Rr to permit the frequency to vary in a wider range.
Rr 185.1 [k
]
Rt [k
]
2.35
3.35A
B
Rr [k
]
2.35
A
B
f
0
[kHz]
4880
RtRr + 1.4
Rr
Rt
fr [kHz]
2500
RtRr + 6
Rr
3.35Rt
B =
f
r
2500
6f
r
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相關代理商/技術參數
參數描述
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
FA-365 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
FA-365 14.31818MHZ 50PPM 16PF 制造商:Epson Toyocom Corporation 功能描述:XTAL FA-365 14.31818MHZ 50PPM 16PF
FA-365 16.0000MB-G3 功能描述:CRYSTAL 16.0000MHZ 20PF SMD RoHS:是 類別:晶體和振蕩器 >> 晶體 系列:FA-365 標準包裝:1 系列:ABLS2 類型:MHz 晶體 頻率:3.579545MHz 頻率穩定性:±30ppm 頻率公差:±30ppm 負載電容:18pF ESR(等效串聯電阻):180 歐姆 工作模式:基諧 工作溫度:-40°C ~ 85°C 額定值:- 安裝類型:表面貼裝 封裝/外殼:HC49/US 尺寸/尺寸:0.449" L x 0.185" W(11.40mm x 4.70mm) 高度:0.130"(3.30mm) 包裝:剪切帶 (CT) 產品目錄頁面:1683 (CN2011-ZH PDF) 其它名稱:535-9855-1
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