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PDF FS8802 Datasheet ( Hoja de datos )

Número de pieza FS8802
Descripción High Efficiency Low Start-up Voltage Step-up DC-DC Converter
Fabricantes Fortune Semiconductor 
Logotipo Fortune Semiconductor Logotipo
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FS8802 datasheet

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FS8802 pdf
FS8802
10. Typical Application Circuit
1~3V
VIN
L1
4.7µH
D1
3.3V
VOUT
C1
+ 100µF
R3
R4
R5
1M
Low Battery
Warning
LX
CE Vout
LBO FS8802 EXT
LBI FB
GND
R6
20K
C4
40pF
C3 C2
1µF + 100µF
R1
560K
R2
330K
Fig 3. FS8802 Typical Application for 3.3V output below 400mA
1~3V
VIN
L1
4.7µH
D1
3.3V
VOUT
C1
+ 100µF
R3
R4
R5
1M
Low Battery
Warning
LX
CE Vout
LBO FS8802 EXT
LBI FB
GND
R6
20K
C4
40pF
Q1
NMOS C3
+ 1µF
R1
560K
R2
330K
Fig 4. 0.4A ~ 2A Output Current Application
Rev. 2.1
5/11

5 Page

FS8802 arduino
FS8802
The FS8802 has internal soft start circuit that limits
current draw at startup, reducing transients on the
input source. Soft-start is particularly useful for
higher impedance input sources, such as Li+ and
alkaline cells. When power is applied to the device,
the soft start circuit first pumps up the output voltage
to approximately 2.2 V at a fixed duty cycle. This is
the voltage level at which the controller can operate
normally. In addition to that, the start up capability
with heavy loads is also improved.
14.4 Shutdown
The FS8802 enters shutdown to reduce quiescent
current to typically 0.1μA when CE pin is low . For
normal operation, drive CE high or connect CE to
VOUT. During shutdown, the reference, low-battery
comparator, gain block, and all feedback and control
circuitry are off. The boost converter’s output drops
to one Schottky diode voltage drop below the input
voltage and LX remains high impedance. The
capacitance and load at VOUT determine the rate at
which VOUT decays. Shutdown can be pulled as high
as 6V, regardless of the voltage at VOUT.
15. Application Information
15.1 Inductor Selection
The FS8802 is designed to work well with a 4.7μH to
10μH inductor in most applications. Low inductance
values supply higher output current, but also
increase the ripple and reduce efficiency. Higher
inductor values reduce ripple and improve efficiency,
but also limit output current. Choose a low
DC-resistance inductor, usually less than 1to
minimize loss. It is necessary to choose an inductor
with saturation current greater than the peak current
that the inductor will encounter in the application.
Saturation occurs when the inductor’s magnetic flux
density reaches the maximum level the core can
support and inductance falls.
15.2 Capacitor Selection
Use a 47uF to 100uF SMT tantalum output capacitor
with about 50mto 150mequivalent series
resistance (ESR) to provide stable switching while
minimizing output ripple. Smaller capacitors are
acceptable for light loads or in applications that can
tolerate higher output ripple. The input capacitor
reduces peak currents and noise at the voltage
source. Input capacitors must meet the input ripple
requirements and voltage rating. The ESR of both
input and output capacitors affects efficiency and
output ripple. Output voltage ripple is the product of
the peak inductor current and the output capacitor
ESR. Use low ESR capacitors for best performance,
or connect two or more output capacitors in parallel.
15.3 Layout Considerations
High switching frequencies make PC board layout a
very important part of design. Good design
minimizes excessive EMI on the feedback paths and
voltage gradients in the ground plane, both of which
can result in instability or regulation errors. Connect
the inductor, input filter capacitor, and output filter
capacitor as close to the device as possible, and
keep their traces short, direct, and wide to reduce
power loss so as to improve efficiency. Connect their
ground pins at a single common node in a star
ground configuration, or at a full ground plane. The
external voltage feedback network should be very
close to the FB pin, within 5mm. Keep noisy traces,
such as the LX trace, away from the voltage
feedback network; also keep them separate, using
grounded copper.
The output capacitor should be placed close to the
output terminals to obtain better smoothing effect on
the output ripple. A 1μF bypass capacitor (Fig. 3 & 4)
should be placed close to the VOUT pin and GND pin
of the FS8802 to filter the switching spikes in the
output voltage to provide more stability.
Rev. 2.1
10/11

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