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PDF ACT4070 Data sheet ( Hoja de datos )
| Número de pieza | ACT4070 | |
| Descripción | Wide Input 3A Step Down Converter | |
| Fabricantes | Active-Semi | |
| Logotipo |  |
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ACT4070
Rev 2, 16-Sep-11
Wide Input 3A Step Down Converter
FEATURES
• 3A Output Current
• Up to 95% Efficiency
• 4.5V to 30V Input Range
• 6µA Shutdown Supply Current
• 400kHz Switching Frequency
• Adjustable Output Voltage
• Cycle-by-Cycle Current Limit Protection
• Thermal Shutdown Protection
• Internal Soft Start Function
• Frequency Fold Back at Short Circuit
• Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
• SOP-8/EP (Exposed Pad) Package
APPLICATIONS
• TFT LCD Monitors or Televisions and HDTV
• Portable DVD Players
• Car-Powered or Battery-Powered Equipment
• Set-Top Boxes
• Telecom Power Supplies
• DSL and Cable Modems and Routers
GENERAL DESCRIPTION
The ACT4070 is a current-mode step-down DC/DC
converter that generates up to 3A output current at
400kHz switching frequency. The device utilizes
Active-Semi’s proprietary ISOBCD30 process for
operation with input voltage up to 30V.
Consuming only 6μA in shutdown mode, the
ACT4070 is highly efficient with peak efficiency at
95% when in operation. Protection features include
cycle-by-cycle current limit, thermal shutdown, and
frequency fold back at short circuit. The device also
includes an internal soft start function to prevent
overshoot.
The ACT4070 is available in SOP-8/EP exposed
pad package and requires very few external de-
vices for operation.
NOTE:
∗ Refer to the last page (Page11) for the End of
Life Notice of the Part Number.
TYPICAL APPLICATION CIRCUIT
Innovative PowerTM
- 1 - www.active-semi.com
Copyright © 2011 Active-Semi, Inc.
1 page  
ACT4070
Rev 2, 16-Sep-11
APPLICATIONS INFORMATION
Output Voltage Setting
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 output voltage:
RFB1
=
RFB2
⎜⎛
⎝
VOUT
1.222V
-1⎟⎞
⎠
Figure 1:
Output Voltage Setting
(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 ripple
factor. Typically, choose KRIPPLE = between 20% and
30% to correspond to the peak-to-peak ripple current
being a percentage of the maximum output current.
With this inductor value (Table 1), the peak inductor
current is IOUT (1 + KRIPPLE / 2). Make sure that this
peak inductor current is less that the 5A current
limit. Finally, select the inductor core size so that it
does not saturate at 5A.
Table 1:
Typical Inductor Values
VOUT
L
1.5V
6.8μH
1.8V
6.8μH
2.5V
6.8μH
3.3V
8.5μH
5V
15μH
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 recom-
mended. Since large current flows in and out of this
capacitor during switching, its ESR also affects effi-
ciency.
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 shortest traces possible. In the
case of tantalum or electrolytic types, they can be
further away if a small parallel 0.1µF ceramic ca-
pacitor 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 RIPPLE
+
28
×
VIN
fSW 2LCOUT
(3)
where IOUTMAX is the maximum output current, KRIPPLE
is the ripple factor, RESR is the ESR resistance of the
output capacitor, fSW is the switching frequency, L in
the inductor value, COUT is the output capacitance. In
the case of ceramic output capacitors, RESR is very
small and does not contribute to the ripple. There-
fore, a lower capacitance value can be used for ce-
ramic type. In the case of tantalum or electrolytic
type, 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 type, typically choose a capaci-
tance of about 22µF. For tantalum or electrolytic type,
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 the reverse volt-
age rating higher than the maximum input voltage.
Innovative PowerTM
- 5 - www.active-semi.com
Copyright © 2011 Active-Semi, Inc.
5 Page 
Active-Semi Shanghai Limited
Innovative Products. Active Solutions.
End of Life (ECL) Notice for ACT4070
Notice date: Sept 05, 2011
Active Semiconductor announces that the end-of-sale and end-of-life dates for the ACT4070:
30V/3A Step-down DC-DC converter. The last day to order the affected product is February 15,
2012. Customers will continue to receive technical support for this product from Active-semi even
if the data exceeds the end-of-sale date.
Table 1 describes the end-of-life milestones and the dates for the affected product.
Table 1. End-of-Life Milestones and Dates for the ACT4070
Milestone
Date
End-of-Life Announcement Date
September 5, 2011
Last Order Date
February 15, 2012
Last Ship Date
May 08, 2012
Affected Market
Global
The Alternative Chipsets
ACT4303, ACT4523
ACT4070A (Available in Q1
2012)
The alternative chipsets of ACT4070 are ACT4303 and ACT4523, which support many advanced
features. For full specification of ACT4303 and ACT4523, please contact with Active-semi sales
representative or Active-semi distributor sales representative.
If you are receiving this announcement but are not involved with product procurement at your
company, it is very important that you forward this to the appropriate person.
·RM1202,Sunplus Building, No.1077 Zuchongzhi Road, Zhangjiang Hi-Tech Park, Shanghai 201203, China;
www.active-semi.com Tel: (86-21) 5108 2797 Fax: (86-21) 5080 5687
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet ACT4070.PDF ] | |
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