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FA3641P Schematic ( PDF Datasheet ) - Fuji Electric

Teilenummer FA3641P
Beschreibung PWM control IC with light load power saving function For Switching Power Supply Control
Hersteller Fuji Electric
Logo Fuji Electric Logo 




Gesamt 21 Seiten
FA3641P Datasheet, Funktion
FA3641P(N), FA3647P(N)FA3641P(N), FA3647P(N)
PWM control IC with light load power saving function
For Switching Power Supply Control
s Description
The FA3641P(N) and FA3647P(N) are the PWM type switching
power supply control ICs that can directly drive power MOSFET.
These ICs use a CMOS device with high dielectric strength
(30V) to implement low power consumption. They feature a
number of functions that are equivalent to those of the FA531X
series consisting of bipolar devices. In addition, they have a
function that reduces the oscillation frequency to suppress loss
of the power supply in light load mode and support an
overvoltage protection detecting Vcc voltage. These ICs are
most suitable for high-performance, energy-saving power
supplies that require low input power in standby or no-load
mode.
s Features
Uses a newly developed CMOS process with high dielectric
strength (30V) for implementing low power consumption
Standby current of 2µA or less (at Vcc=14V), and operating
current of 1.9mA (typ.)
Automatically reduces the oscillation frequency to suppress
loss of the power supply in light load mode
Overvoltage protection function detecting Vcc voltage
A drive circuit for connecting a power MOSFET directly
Output peak current: Source current 500mA
Sink current
+1A
Pulse-by-pulse overcurrent limiting function
Overload cutoff function (latch or non-latch mode selectable)
Output ON/OFF control function by external signal
Latch mode overvoltage shutdown function
Undervoltage lockout function
(16.5V ON / 9V OFF)
Reference voltage output (5V)
8-pin package (DIP/SOP)
s Dimensions, mm
SOP-8
85
14
4.9
0.4±0.1 1.27±0.2
DIP-8
8
5
1 9.3 4
1.5
2.54±0.25 0.46±0.1
7.62
0~15˚
0.25+00.1.05
0~15˚
58






FA3641P Datasheet, Funktion
Supply current (Icc) vs. supply voltage (Vcc)
Latch mode
200
160
120
80
40
0
10 12 14 16 18 20
Vcc [V]
Supply current (Icc) vs. supply voltage (Vcc)
OFF mode
200
160
120
80
40
0
10 12 14 16 18 20
Vcc [V]
UVLO OFF-to-ON thrreshold voltage (Vcc on) vs.
junction temperature (Tj)
1.7
16.8
16.6
16.4
16.2
16
50
0 50 100 150
Tj [°C]
FA3641P(N), FA3647P(N)
Supply current (Icc) vs. supply voltage (Vcc)
Latch mode
3000
2500
2000
1500
1000
500
0
10 15 20
25 30
Vcc [V]
Supply current (Icc) vs. supply voltage (Vcc)
OFF mode
3000
2500
2000
1500
1000
500
0
10 15 20
25 30
Vcc [V]
UVLO ON-to-OFF thrreshold voltage (Vcc off) vs.
junction temperature (Tj)
9.2
9.1
9
8.9
8.8
50
0 50 100 150
Tj [°C]
63

6 Page









FA3641P pdf, datenblatt
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.
s 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:
Rt [k] Լ
2.35
3.35A B
Rr [k] Լ
2.35 ............................ (5)
AB
f0 [kHz] Լ
4880
fr [kHz] Լ
RtRr + 1.4
2500
RtRr
....... (6)
+6
Rr Rt
Rr 3.35Rt
fO: Fixed frequency [kHz]
fr: Minimum frequency in variable mode [kHz]
Rt: Timing resistance [k]
Rr: Adjustment resistance [k]
A = f0
B = fr
4880 1.4f0
2500 6fr
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 fO = 100kHz and minimum frequency
in light-load mode to fr = 20kHz, the following can be obtained
from expressions (5).
Rt Լ 37.7 [k]
Rr Լ 185.1 [k]
Decrease Rr to permit the frequency to vary in a wider range.
FA3641P(N), FA3647P(N)
Fig. 18 Oscillator circuit
69

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