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FA5305AP Schematic ( PDF Datasheet ) - Fuji Electric

Teilenummer FA5305AP
Beschreibung Bipolar IC For Switching Power Supply Control
Hersteller Fuji Electric
Logo Fuji Electric Logo 




Gesamt 17 Seiten
FA5305AP Datasheet, Funktion
FA5304AP(S)/FA5305AP(S) Bipolar IC
For SwitcFhAin5g30P4oAwPe(rSS)/uFpAp5l3y0C5oAnPt(rSo)l
s Description
The FA5304AP(S) and FA5305AP(S) are bipolar ICs for
switching power supply control and can directly drive a power
MOSFET. These ICs contain many functions in a small 8-pin
package. With these ICs, a high-performance power supply
can be created compactly because not many external
components are needed.
s Features
• Drive circuit for connecting a power MOS-FET (IO = ±1.5A)
• Wide operating frequency range (5 to 600kHz)
• Pulse-by-pulse overcurrent limiting function
Positive voltage detection: FA5304AP(S)
Negative voltage detection: FA5305AP(S)
• Overload cutoff function (Latch or non-protection mode
selectable)
• Output ON/OFF control function by external signals
• Overvoltage cutoff function in latch mode
• Undervoltage malfunction prevention function (ON at 16V
and OFF at 8.7V)
• Error amplifier for control by tertiary winding detection
• Low standby current (90µA typ.)
• 8-pin package (DIP/SOP)
s Applications
• Switching power supply for general equipment
s Dimensions, mm
SOP-8
8
5
14
6.05
0.4±0.1 1.27±0.2
DIP-8
8
5
1 9.3 4
1.5
0.6
2.54±0.25 0.5±0.1
0~15˚
7.6
0.3 +–00.1.05
0~15˚
1






FA5305AP Datasheet, Funktion
FA5304AP(S)/FA5305AP(S)
4. CS pin circuit
As shown in Figure 5, capacitor CS is connected to the CS pin.
When power is turned on, the constant current source (10µA)
begins to charge capacitor CS. Accordingly, the CS pin voltage
rises as shown in Figure 6. The CS pin is connected to an
input of the PWM comparator. The device is in soft-start mode
while the CS pin voltage is between 1.0V and 1.9V common to
FA5304A and FA5305A. During normal operation, the CS pin
is clamped at 3.6V by internal zener diode Zn. If the output
voltage drops due to an overload, etc., the clamp voltage shifts
from 3.6V to 8.0V. As a result, the CS pin voltage rises to 8.0V.
The CS pin is also connected to latch comparator C2. If the pin
voltage rises above 7.0V, the output of comparator C2 goes
high to turn off the bias circuit , thereby shutting the output
down. Comparator C2 can be used not only for shutdown in
response to an overload, but also for shutdown in response to
an overvoltage. Comparator C1 is also connected to the CS
pin, and the bias circuit is turned off and the output is shut
down if the CS pin voltage drops below 0.42V. In this way,
comparator C1 can also be used for output on/off control.
As explained above, the CS pin can be used for soft-start
operation, overload and overvoltage output shutdown and
output on/off control.
Further details on the four functions of the CS pin are given
below.
4.1 Soft start function
Figure 7 shows the soft start circuit. Figure 8 is the soft-start
operation timing chart. The CS pin is connected to capacitor
CS . When power is turned on, a 10µA constant-current source
begins to charge the capacitor. As shown in the timing chart,
the CS pin voltage rises slowly in response to the charging
current. The CS pin is connected internally to the PWM
comparator. The comparator output pulse slowly widens as
shown in the timing chart.
The soft start period can be approximately evaluated by the
period ts from the time the IC is activated to the time the output
pulse width widens to 30%. Period ts is given by the following
equation:
tS (mS) = 160CS (µF).................................(2)
Fig. 5 CS pin circuit
Fig. 6 CS pin waveform
Fig. 7 Soft-start circuit
Fig. 8 Soft-start timing chart
6

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FA5305AP pdf, datenblatt
FA5304AP(S)/FA5305AP(S)
2. Disabling overload shutdown function
As shown in Figure 24, connect a 330kto 470kresistor
between the CS pin and ground. Then, the CS pin voltage
does not rise high enough to reach the reference voltage
(7.0V) of the latch comparator, and the IC does not enter the
OFF latch mode. With this connection, the overvoltage
shutdown function is not available.
3. Setting soft start period and OFF latch delay
independently
Figure 25 shows a circuit for setting the soft start period and
OFF latch delay independently. In this circuit, capacitance CS
determines the soft start period, and capacitance CL
determines the OFF latch delay. If the overload shutdown and
overvoltage shutdown functions raise the CS pin voltage to
around 5V, zener diode Zn becomes conductive to charge CL.
The OFF latch delay can be thus prolonged by CL.
4. Laying out Vcc and ground lines
Figure 26 and Figure 27 show the recommended layouts of
VCC and ground lines. The bold lines represent paths carrying
large currents. The lines must have an adequate thickness.
5. Sink current setting for CS terminal
A sink current to CS terminal must be satisfied the following
condition to prevent from the malfunction which uncontrolled
pulse output generates at OUT terminal when latch-mode
protection should be operated for overvoltage.
150µA < Ics(sink) < 500µA at Vcs= 6.5(V)
Ics(sink): Sink current to CS terminal
Example (for the circuit shown in Fig. 28 )
Ics(sink) = (28(V)–18(V)– 6.5(V))/7.5(k)
Լ 467 (µA) < 500 (µA)
Fig. 25 Independent setting of soft-start period and OFF latch
delay
Fig. 26 Vcc line and ground line for FA5304A
Fig. 24 Disabling overload shutdown function
12
Fig. 27 Vcc line and ground line for FA5305A
CS
VCC
7.5k18V Zener diode
Under 500µA
Fig. 28 Setting sink current for CS terminal

12 Page





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