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PDF ( 数据手册 , 数据表 ) FA13845P

零件编号 FA13845P
描述 CMOS IC(For Switching Power Supply Control)
制造商 Fuji Electric
LOGO Fuji Electric LOGO 


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FA13845P 数据手册, 描述, 功能
FA13842,13843,13844,13845
CMOS IC
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s Description
The FA1384X series are CMOS current mode control ICs for
off-line and DC-to-DC converters.
These ICs can reduce start-up circuit loss and are optimum for
high efficiency power supplies because of the low power
dissipation achieved through changes in the CMOS fabrication
process.
These ICs can drive a power MOSFET directly.
The high-performance, compact power supply can be
designed with minimal external components .
s Features
• CMOS process
• Low-power dissipation
• Standby current 2µA (max.), start-up current 30µA (max.)
• Pulse-by-pulse current limiting
• 5V bandgap reference
• UVLO (Undervoltage lockout) with hysteresis
• Maximum duty cycle FA13842, 13843: 96%
FA13844, 13845: 48%
• Pin-for-pin compatible with UC384X
Note: Pins are fully compatible, but characteristics are not.
When our ICs are applied to a power supply circuit
designed for other manufactures' 384X series, the
characteristics and safety features of the power supply
must be checked.
s Types of FA1384X series
Type
UVLO
Maximum duty Package
Start threshold Stop threshold cycle
FA13842P 16.5V±1V
9V± 1V
96%
DIP
FA13842N
SOP
FA13843P 9.6V±1V
9V± 1V
96%
DIP
FA13843N
SOP
FA13844P 16.5V±1V
9V± 1V
48%
DIP
FA13844N
SOP
FA13845P 9.6V±1V
9V± 1V
48%
DIP
FA13845N
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˚
1







FA13845P pdf, 数据表
FA13842, 13843, 13844, 13845
s Description of each circuit
1. Oscillator
The oscillation frequency is determined by timing resistance RT
and timing capacitor CT, which are connected to RT/CT
terminal. CT is charged to about 3V through RT from a 5V
reference, and discharged to about 1.4V by the built-in
discharge circuit. (See Fig. 1, 2, 3.)
Blanking pulses are generated in the IC during the CT
discharge period.
The output is fixed in the “low” state by these pulses, and a
fixed dead time is produced. See the characteristic curves on
page 45 for the oscillation frequency, RT and CT.
In the case of FA13844/45, a flip-flop causes the output to be
blanked with every other cycle. Therefore, the switching
frequency of a power MOSFET is 1/2 of the oscillation
frequency determined by RT and CT. (See Fig. 3.)
2. Error amplifier
Inverting input and output are connected to the FB terminal
and COMP terminal, respectively. A 2.5V reference is
connected internally to the non-inverting input.
The output voltage is offset by a diode VF voltage (=0.7V) and
divided by three. The divided voltage is connected to the input
of the current sensing comparator.
3. Current sensing comparator and PWM latch
The “High” state of the OUT terminal begins at the time CT
starts charging. The OUT terminal turns to “Low” when the
peak inductor current reaches the threshold level controlled by
the error amplifier output (COMP terminal).
The inductor current is converted to a voltage by sensing
resistor RS inserted between GND and the source of a power
MOSFET. This voltage is monitored by the ISNS terminal.
The peak current of inductor “Ipk” is expressed as follows:
Ipk=(Vcomp–0.7) / (3•RS)
0.7V VF
Vcomp: a voltage on COMP terminal
The maximum value of the threshold level of the current
sensing comparator is held to 1V. Therefore, the maximum
peak current “Ipk(max)” is as follows:
Ipk(max)=1.0V/RS
4. Undervoltage lockout (UVLO)
In order to set the IC in the operation mode before the output
stage(OUT terminal) is enabled, two under-voltage lockout
comparators are incorporated to monitor the power supply
voltage (VCC) and reference voltage (VREF).
The threshold level of the VCC comparator is set at 16.5V/9V for
FA13842/44 and 9.6V/9V for FA13843/45. In the standby
mode, in which the VCC is under ON threshold, the power
supply current is maintained at nearly 0 (zero). However, a
maximum current of 30µA is required to change from standby
mode to operating mode .
The threshold level of the VREF comparator is set at about 3.2V/
2.0V.
A 30V zener diode is connected to VCC and GND to protect the
IC against overvoltages.
Vcc Vin
VCC
7
30V
UVLO
UVLO
VCC 5V REF
ENB 2.5V
OUTPUT
ENB
VREF
8
6 OUT
RT
RT/CT
4
CT
FB 2
COMP 1
ISNS 3
ER AMP 2R
1R
OSC
1V
SQ
FF
R QB
5 GND
RS
Fig. 1
3V
CT
1.4V
Set
COMP
ISENS
Reset
OUT
CT
Set
Fig. 2 FA13842, 13843
3V
1.4V
COMP
ISENS
Reset
OUT
Fig. 3 FA13844, 13845
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