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PDF AAT1141 Data sheet ( Hoja de datos )
| Número de pieza | AAT1141 | |
| Descripción | Fast Transient 600mA Step-Down Converter | |
| Fabricantes | Advanced Analog Technology | |
| Logotipo |  |
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SwitchRegTM
PRODUCT DATASHEET
AAT1141
Fast Transient 600mA Step-Down Converter
General Description
The AAT1141 SwitchReg is a 1.4MHz step-down con-
verter with an input voltage range of 2.7V to 5.5V and
output voltage as low as 0.6V. It is optimized to react
quickly to a load variation.
The AAT1141 is available in fixed voltage versions with
internal feedback and a programmable version with
external feedback resistors. It can deliver 600mA of load
current while maintaining a low 35μA no load quiescent
www.DatacSuhrereet4nUt..coTmhe 1.4MHz switching frequency minimizes the
size of external components while keeping switching
losses low.
The AAT1141 is designed to maintain high efficiency
throughout the operating range, which is critical for por-
table applications.
The AAT1141 is available in a Pb-free SOT23-5 package
and is rated over the -40°C to +85°C temperature
range.
Features
• VIN Range: 2.7V to 5.5V
• VOUT Fixed or Adjustable from 0.6V to VIN
• 35μA No Load Quiescent Current
• Up to 98% Efficiency
• 600mA Max Output Current
• 1.4MHz Switching Frequency
• 120μs Soft Start
• Fast Load Transient
• Over-Temperature Protection
• Current Limit Protection
• 100% Duty Cycle Low-Dropout Operation
• <1μA Shutdown Current
• SOT23-5 Package
• Temperature Range: -40°C to +85°C
Applications
• Cellular Phones
• Digital Cameras
• Handheld Instruments
• Microprocessor / DSP Core / IO Power
• PDAs and Handheld Computers
• USB Devices
Typical Application (Fixed Output Voltage)
VIN
C2
4.7µF
U1
AAT1141
IN LX
EN
GND
OUT
L1
4.7µH
VOUT
C1
4.7µF
1141.2007.12.1.3
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1 page  
SwitchRegTM
Typical Characteristics
Efficiency vs. Load
(VOUT = 3.3V; L = 6.8μH)
100
VIN = 3.6V
90
VIN = 4.2V
80
VIN = 5.0V
www.DataShe7e0t4U.com
60
50
0.1
1 10 100
Output Current (mA)
1000
Efficiency vs. Load
(VOUT = 2.5V; L = 6.8μH)
100
VIN = 2.7V
90
80 VIN = 5.0V
VIN = 4.2V
70 VIN = 3.6V
60
50
0.1
1 10 100
Output Current (mA)
1000
Efficiency vs. Load
(VOUT = 1.8V; L = 4.7μH)
100
VIN = 2.7V
90
80 VIN = 3.6V VIN = 4.2V
70
60
50
0.1
1 10 100
Output Current (mA)
1000
PRODUCT DATASHEET
AAT1141
Fast Transient 600mA Step-Down Converter
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
0
DC Regulation
(VOUT = 3.3V; L = 6.8µH)
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
100 200 300 400 500
Output Current (mA)
600
DC Regulation
(VOUT = 2.5V; L = 6.8µH)
3.0
2.0
1.0 VIN = 5.0V
0.0
-1.0 VIN = 3.0V
-2.0
VIN = 3.6V
VIN = 4.2V
-3.0
0
100 200 300 400 500 600
Output Current (mA)
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
0
DC Regulation
(VOUT = 1.8V; L = 4.7μH)
VIN = 2.7V VIN = 3.6V
VIN = 4.2V
100 200 300 400 500
Output Current (mA)
600
1141.2007.12.1.3
www.analogictech.com
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5 Page 
SwitchRegTM
PRODUCT DATASHEET
AAT1141
Fast Transient 600mA Step-Down Converter
Applications Information
Inductor Selection
The step-down converter uses peak current mode con-
trol with slope compensation to maintain stability for
duty cycles greater than 50%. The output inductor value
must be selected so the inductor current down slope
meets the internal slope compensation requirements.
The internal slope compensation for the adjustable and
www.DataSlohwee-tv4oUl.tcaogme fixed versions of the AAT1141 is 0.24A/μsec.
This equates to a slope compensation that is 75% of the
inductor current down slope for a 1.5V output and 4.7μH
inductor.
m=
0.75 ⋅
L
VO
=
0.75 ⋅ 1.5V
4.7μH
=
0.24
A
μsec
This is the internal slope compensation for the adjust-
able (0.6V) version or low-voltage fixed versions. When
externally programming the 0.6V version to 2.5V, the
calculated inductance is 7.5μH.
L=
0.75 ⋅ VO
m
=
0.75 ⋅ VO
A
≈
3
μsec
A
⋅
VO
0.24A μsec
=
3
μsec
A
⋅ 2.5V = 7.5μH
In this case, a standard 6.8μH value is selected.
For high-voltage fixed versions (≥2.5V), m = 0.48A/
μsec. Table 1 displays inductor values for the AAT1141
fixed and adjustable options.
Manufacturer's specifications list both the inductor DC
current rating, which is a thermal limitation, and the
peak current rating, which is determined by the satura-
tion characteristics. The inductor should not show any
appreciable saturation under normal load conditions.
Some inductors may meet the peak and average current
ratings yet result in excessive losses due to a high DCR.
Always consider the losses associated with the DCR and
its effect on the total converter efficiency when selecting
an inductor.
The 4.7μH CDRH2D14 series inductor selected from
Sumida has a 135mΩ typical DCR and a 1A DC current
rating. At full load, the inductor DC loss is 48mW which
gives a 4.5% loss in efficiency for a 600mA, 1.8V output.
Configuration
0.6V Adjustable With
External Feedback
Fixed Output
Output
Voltage
1V, 1.2V
1.5V, 1.8V
2.5V, 3.3V
0.6V to 3.3V
Inductor
2.2μH
4.7μH
6.8μH
4.7μH
Table 1: Inductor Values.
Input Capacitor
Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for
the input. To estimate the required input capacitor size,
determine the acceptable input ripple level (VPP) and solve
for C. The calculated value varies with input voltage and
is a maximum when VIN is double the output voltage.
CIN =
VO
VIN
· ⎛⎝1 -
VO ⎞
VIN ⎠
⎛ VPP
⎝ IO
- ESR⎞⎠ · FS
VO
VIN
·
⎛⎝1 -
VO ⎞
VIN ⎠
=
1
4
for
VIN
=
2
·
VO
CIN(MIN) = ⎛ VPP
⎝ IO
1
- ESR⎞⎠ · 4 · FS
Always examine the ceramic capacitor DC voltage coeffi-
cient characteristics when selecting the proper value. For
example, the capacitance of a 10μF, 6.3V, X5R ceramic
capacitor with 5.0V DC applied is actually about 6μF.
The maximum input capacitor RMS current is:
IRMS = IO ·
VO
VIN
· ⎛⎝1 -
VO ⎞
VIN ⎠
The input capacitor RMS ripple current varies with the
input and output voltage and will always be less than or
equal to half of the total DC load current.
VO
VIN
· ⎛⎝1 -
VO ⎞
VIN ⎠
=
D · (1 - D) =
0.52
=
1
2
for VIN = 2 · VO
I =RMS(MAX)
IO
2
The term
VO
VIN
·
⎛⎝1 -
VO ⎞
VIN ⎠
appears in both the input voltage
ripple and input capacitor RMS current equations and is
1141.2007.12.1.3
www.analogictech.com
11
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet AAT1141.PDF ] | |
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