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參數(shù)資料
| 型號： | FA3641P |
| 廠商： | FUJI ELECTRIC CO LTD |
| 元件分類： | 穩(wěn)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(shù)： | 12/21頁 |
| 文件大?。?/td> | 406K |
| 代理商： | FA3641P |
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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| FA3641P_00 | 制造商:FUJI 制造商全稱:Fuji Electric 功能描述:PUJI Power Supply Controllc |
| FA3641P-D1 | 制造商:Fuji Electric 功能描述: |
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| 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: |
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