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PDF ACT4060 Data sheet ( Hoja de datos )
| Número de pieza | ACT4060 | |
| Descripción | Wide Input 2A Step Down Converter | |
| Fabricantes | Active-Semi | |
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ACT4060
Rev8, 24-Jul-07
Wide Input 2A Step Down Converter
FEATURES
2A Output Current
Up to 95% Efficiency
4.75V to 20V Input Range
8µA Shutdown Supply Current
420kHz Switching Frequency
Adjustable Output Voltage
Cycle-by-Cycle Current Limit Protection
Thermal Shutdown Protection
Frequency FoldBack at Short Circuit
Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
SOP-8 Package
GENERAL DESCRIPTION
The ACT4060 is a current-mode step-down DC/DC
converter that generates up to 2A of output current
at 420kHz switching frequency. The device utilizes
Active-Semi’s proprietary ISOBCD20 process for
operation with input voltages up to 20V.
Consuming only 8μA in shutdown mode, the
ACT4060 is highly efficient with peak operating effi-
ciency at 95%. Protection features include cycle-by-
cycle current limit, thermal shutdown, and frequency
foldback at short circuit.
The ACT4060 is available in a SOP-8 package and
requires very few external devices for operation.
APPLICATIONS
TFT LCD Monitors
Portable DVDs
Car-Powered or Battery-Powered Equipments
Set-Top Boxes
Telecom Power Supplies
DSL and Cable Modems and Routers
Termination Supplies
TYPICAL APPLICATION CIRCUIT
Innovative Products. Active Solutions.
-1-
www.active-semi.com
Copyright © 2006 Active-Semi, Inc.
1 page  
ACT4060
Rev8, 24-Jul-07
APPLICATIONS INFORMATION
Output Voltage Setting
Figure 1:
Output Voltage Setting
VOUT
ACT4060
FB
RFB1
RFB2
Figure 1 shows the connections for setting the out-
put voltage. Select the proper ratio of the two feed-
back resistors RFB1 and RFB2 based on the output
voltage. Typically, use RFB2 ≈ 10kΩ and determine
RFB1 from the following equation:
R FB1
R FB 2
VOUT
1.293V
1
(1)
Inductor Selection
The inductor maintains a continuous current to the
output load. This inductor current has a ripple that is
dependent on the inductance value: higher induc-
tance reduces the peak-to-peak ripple current. The
trade off for high inductance value is the increase in
inductor core size and series resistance, and the
reduction in current handling capability. In general,
select an inductance value L based on ripple current
requirement:
L VOUT VIN VOUT
V f I KIN SW OUTMAX RIPPLE
(2)
where VIN is the input voltage, VOUT is the output
voltage, fSW is the switching frequency, IOUTMAX is
the maximum output current, and KRIPPLE is the rip-
ple factor. Typically, choose KRIPPLE = 30% to corre-
spond to the peak-to-peak ripple current being 30%
of the maximum output current.
With this inductor value, the peak inductor current is
IOUT × (1 + KRIPPLE/2). Make sure that this peak in-
ductor current is less that the 3A current limit. Fi-
nally, select the inductor core size so that it does
not saturate at 3A. Typical inductor values for vari-
ous output voltages are shown in Table 1.
Table 1:
Typical Inductor Values
VOUT 1.5V
L 6.8μH
1.8V
6.8μH
2.5V
10μH
3.3V
15μH
5V
22μH
Input Capacitor
The input capacitor needs to be carefully selected
to maintain sufficiently low ripple at the supply input
of the converter. A low ESR capacitor is highly rec-
ommended. Since large current flows in and out of
this capacitor during switching, its ESR also affects
efficiency.
The input capacitance needs to be higher than
10µF. The best choice is the ceramic type, how-
ever, low ESR tantalum or electrolytic types may
also be used provided that the RMS ripple current
rating is higher than 50% of the output current. The
input capacitor should be placed close to the IN and
G pins of the IC, with the shortest traces possible.
In the case of tantalum or electrolytic types, they
can be further away if a small parallel 0.1µF ce-
ramic capacitor is placed right next to the IC.
Output Capacitor
The output capacitor also needs to have low ESR to
keep low output voltage ripple. The output ripple
voltage is:
V I K RRIPPLE OUTMAX RIPPLE ESR
VIN
28 fSW 2 LCOUT
(3)
where IOUTMAX is the maximum output current, KRIP-
PLE is the ripple factor, RESR is the ESR of the output
capacitor, fSW is the switching frequency, L is the
inductor value, and COUT is the output capacitance.
In the case of ceramic output capacitors, RESR is
very small and does not contribute to the ripple.
Therefore, a lower capacitance value can be used
for ceramic type. In the case of tantalum or electro-
lytic capacitors, the ripple is dominated by RESR
multiplied by the ripple current. In that case, the
output capacitor is chosen to have sufficiently low
ESR.
For ceramic output capacitor, typically choose a
capacitance of about 22µF. For tantalum or electro-
lytic capacitors, choose a capacitor with less than
50mΩ ESR.
Rectifier Diode
Use a Schottky diode as the rectifier to conduct cur-
rent when the High-Side Power Switch is off. The
Schottky diode must have current rating higher than
the maximum output current and a reverse voltage
rating higher than the maximum input voltage.
Innovative Products. Active Solutions.
-5-
www.active-semi.com
Copyright © 2006 Active-Semi, Inc.
5 Page | ||
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| PDF Descargar | [ Datasheet ACT4060.PDF ] | |
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