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PDF ACT4060A Data sheet ( Hoja de datos )
| Número de pieza | ACT4060A | |
| Descripción | Wide Input 2A Step Down Converter | |
| Fabricantes | Active-Semi | |
| Logotipo |  |
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ACT4060A
Rev 1, 25-Jun-09
Wide Input 2A Step Down Converter
FEATURES
• 2A Output Current
• Up to 96% Efficiency
• 4.5V to 24V Input Range
• 10µA Shutdown Supply Current
• 400kHz 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
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
GENERAL DESCRIPTION
The ACT4060A is a current-mode step-down
DC/DC converter that provides up to 2A of output
current at 400kHz switching frequency. The device
utilizes Active-Semi’s proprietary high voltage
process for operation with input voltages up to 24V.
The ACT4060A provides fast transient response
and eases loop stabilization while providing
excellent line and load regulation. This device
features a very low ON-resistance power MOSFET
which provides peak operating efficiency up to 96%.
In shutdown mode, the ACT4060A consumes only
10μA of supply current.
This device also integrates protection features
including cycle-by-cycle current limit, thermal
shutdown and frequency fold-back at short circuit.
The ACT4060A is available in a SOP-8 package
and requires very few external devices for
operation.
TYPICAL APPLICATION CIRCUIT
Up to 24V
ENABLE
BS
IN SW
ACT4060A
EN FB
G COMP
+
2.5V/2A
Innovative PowerTM
- 1 - www.active-semi.com
Copyright © 2009 Active-Semi, Inc.
1 page  
ACT4060A
Rev 1, 25-Jun-09
APPLICATIONS INFORMATION
Output Voltage Setting
Figure 1:
Output Voltage Setting
VOUT
ACT4060A
FB
RFB1
RFB2
Figure 1 shows the connections for setting the
output voltage. Select the proper ratio of the two
feedback 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
inductance 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
ripple factor. Typically, choose KRIPPLE = 30% to
correspond 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
inductor current is less that the 3A current limit.
Finally, select the inductor core size so that it does
not saturate at 3A. Typical inductor values for
various output voltages are shown in Table 1.
Table 1:
Typical Inductor Values
VOUT
L
1.5V
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
recommended. 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,
however, 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 ceramic 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
+
28
×
VIN
fSW 2 LCOUT
(3)
where IOUTMAX is the maximum output current,
KRIPPLE 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 electrolytic 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
electrolytic capacitors, choose a capacitor with less
than 50mΩ ESR.
Rectifier Diode
Use a Schottky diode as the rectifier to conduct
current 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 PowerTM
- 5 - www.active-semi.com
Copyright © 2009 Active-Semi, Inc.
5 Page 
ACT4060A
Rev 1, 25-Jun-09
TYPICAL PERFORMANCE CHARACTERISTICS CONT’D
(Circuit of Figure 4, unless otherwise specified.)
Shutdown Current vs. Input Voltage
25
20
15
10
5
0
5 10 15 20 25
Input Voltage (V)
Innovative PowerTM
- 11 -
www.active-semi.com
Copyright © 2009 Active-Semi, Inc.
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet ACT4060A.PDF ] | |
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