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PDF ACT6907 Data sheet ( Hoja de datos )
| Número de pieza | ACT6907 | |
| Descripción | 600mA Synchronous Step Down Converter | |
| Fabricantes | Active-Semi | |
| Logotipo |  |
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Data Sheet
Rev 0, 5/2006
ACT6907
1.6MHz, 600mA Synchronous
Step Down Converter in SOT23-5
FEATURES
High Efficiency - Up to 95%
Very Low 24µA Quiescent Current
Guaranteed 600mA Output Current
1.6MHz Constant Frequency Operation
Internal Synchronous Rectifier Eliminates
Schottky Diode
Adjustable Output Voltages From 0.6V to VIN
Fixed Output Voltage Options Available
100% Duty Cycle Low-Dropout Operation
0.1µA Shutdown Current
Tiny SOT23-5 Package
APPLICATIONS
Blue Tooth Headsets
Portable Audio Players
Mobile Phones
Wireless and DSL Modems
Digital Still Cameras
Portable Instruments
GENERAL DESCRIPTION
The ACT6907 is a fixed-frequency current-
mode synchronous PWM step down converter
that is capable of delivering 600mA of output
current while achieving peak efficiency of 95%.
Under light load conditions, the ACT6907
operates in a proprietary pulse skipping mode
that consumes just 24µA of supply current,
maximizing battery life in portable applications.
The ACT6907 operates with a fixed frequency of
1.6MHz, minimizing noise in noise-sensitive
applications and allowing the use of small
external components. The ACT6907 is an ideal
solution for applications powered by Li-Ion
batteries or other portable applications that
require small board space.
The ACT6907 is available in a variety of fixed
output voltage options, 1.5V, 1.8V, 2.5V, 2.7V,
2.8V, and 3.3V, and is also available in an
adjustable output voltage version capable of
generating output voltages from 0.6V to VIN .The
ACT6907 is available in the tiny 5-pin SOT23-5
package.
VIN
ENABLE
IN SW
ACT6907
EN FB
G
CIN
L
VOUT
COUT
Figure 1. Typical Application Circuit and Efficiency
Active-Semi, Inc.
- 1 - www.active-semi.com
1 page  
ACT6907
APPLICATION INFORMATION
INDUCTOR SELECTION
Under normal operation, the inductor
maintains continuous current to the output. This
inductor current has a ripple that is dependent
on the inductance value: higher inductance
reduces the peak-to-peak ripple current. In
general, select an inductance value L based on
ripple current requirement:
L
=
VOUT • (VIN − VOUT )
VINfSW IOUTMAX KRIPPLE
(1)
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 (Table 1), the peak
inductor current is IOUT • (1 + KRIPPLE / 2). Make
sure that this peak inductor current is less than
the 0.9A current limit. Finally, select the inductor
core size so that it does not saturate at the
current limit value.
Table 1. Typical Inductor Values
VOUT 0.6V to 0.9V 0.9V to 1.8V
L 1.5μH
2.2μH
>1.8V
2.7μH
INPUT CAPACITOR SELECTION
The input capacitor reduces input voltage
ripple to the converter; a 4.7μF ceramic
capacitor is recommended for most applications.
The input capacitor should be placed as close as
possible to IN and G, with short, wide traces.
OUTPUT CAPACITOR SELECTION
A low ESR output capacitor is required in
order to maintain low output voltage ripple.
Output ripple voltage is given by:
VRIPPLE = IOUTMAX K RIPPLE RESR
+
VIN
28 • f SW 2 LCOUT
(2)
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 is acceptable when ceramic
capacitors are used. A 10µF ceramic output
capacitor is suitable for most applications.
OUTPUT VOLTAGE PROGRAMMING
V
OUT
AACCTT66990067
FB
R
FB1
R
FB2
Figure 3. Output Voltage Programming
Figure 3 shows the feedback network
necessary to set the output voltage when the
adjustable version is used. Select the proper
ratio of the two feedback resistors RFB1 and RFB2
based on the desired output voltage. Typically
choose RFB2 ≈ 100kΩ and determine RFB1 from
the output voltage:
RFB1
=
RFB2
VOUT
0.6V
− 1
(3)
Connect a small capacitor across RFB1 for Feed
forward capacitance at the FB pin:
Cff = 2E − 5/RFB1
(4)
where RFB1 = 900KΩ, use 22pF. When using very
low ESR output capacitors, such as ceramic,
check for stability while examining load-transient
response, and increase the compensation
capacitor C1 if needed.
Active-Semi, Inc.
- 5 - www.active-semi.com
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet ACT6907.PDF ] | |
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