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PDF AAT2146 Data sheet ( Hoja de datos )
| Número de pieza | AAT2146 | |
| Descripción | Fast Transient 600mA Step-Down Converter | |
| Fabricantes | Advanced Analogic Technologies | |
| Logotipo |  |
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PRODUCT DATASHEET
AAT2146
SwitchRegTM
www.DataSheet4U.com
Low Noise, Fast Transient 600mA Step-Down Converter
General Description
The AAT2146 SwitchReg is a 2MHz step-down converter
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 AAT2146 incorporates a unique low
noise architecture which reduces ripple and spectral
noise.
The AAT2146 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 37μA no load quiescent
current. The 2MHz switching frequency minimizes the
size of external components while keeping switching
losses low.
The AAT2146 is designed to maintain high efficiency
throughout the operating range, which is critical for por-
table applications.
The AAT2146 is available in the Pb-free, space-saving
2.0x2.1mm SC70JW-8 package and is rated over the
-40°C to +85°C temperature range.
Features
• VIN Range: 2.7V to 5.5V
• Low Noise Light Load Mode
• Low Ripple PWM Mode
• VOUT Fixed or Adjustable from 0.6V to VIN
• 37μA No Load Quiescent Current
• Up to 98% Efficiency
• 600mA Max Output Current
• 2MHz Switching Frequency
• 150μs Soft Start
• Fast Load Transient
• Over-Temperature Protection
• Current Limit Protection
• 100% Duty Cycle Low-Dropout Operation
• <1μA Shutdown Current
• SC70JW-8 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)
U1
AAT2146
VIN VIN LX
C2
2.2µF
EN OUT
AGND PGND
PGND PGND
L1
4.7µH
VO
C1
4.7µF
2146.2008.10.1.2
www.analogictech.com
1
1 page  
PRODUCT DATASHEET
AAT2146
SwitchRegTM
www.DataSheet4U.com
Low Noise, Fast Transient 600mA Step-Down Converter
Typical Characteristics
100
90
80
70
60
50
40
30
0.1
Efficiency vs. Output Current
(VOUT = 1.8V)
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
1 10 100
Output Current (mA)
1000
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0.1
Load Regulation
(VOUT = 1.8V)
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
1 10 100
Output Current (mA)
1000
100
90
80
70
60
50
40
30
0.1
Efficiency vs. Output Current
(VOUT = 2.5V)
VIN = 3V
VIN = 3.6V
VIN = 4.2V
VIN = 5V
1 10 100
Output Current (mA)
1000
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0.1
Load Regulation
(VOUT = 2.5V)
VIN = 3V
VIN = 3.6V
VIN = 4.2V
VIN = 5V
1 10 100
Output Current (mA)
1000
100
90
80
70
60
50
40
30
0.1
Efficiency vs. Output Current
(VOUT = 3.3V)
VIN = 3.6V
VIN = 4.2V
VIN = 5V
1 10 100
Output Current (mA)
1000
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0.1
Load Regulation
(VOUT = 3.3V)
VIN = 3.6V
VIN = 4.2V
VIN = 5V
1 10 100
Output Current (mA)
1000
2146.2008.10.1.2
www.analogictech.com
5
5 Page 
PRODUCT DATASHEET
AAT2146
SwitchRegTM
www.DataSheet4U.com
Low Noise, 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
low-voltage fixed versions of the AAT2146 is 0.24A/μs.
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
µs
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 ⋅
m
VO
=
0.75 ⋅ VO
A
≈
3
µs
A
⋅
VO
0.24A µs
=
3
µs
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/μs.
Table 1 displays inductor values for the AAT2146 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 CDRH3D16 series inductor selected from
Sumida has a 105mΩ DCR and a 900mA DC current rat-
ing. At full load, the inductor DC loss is 17mW which
gives a 2.8% loss in efficiency for a 400mA, 1.5V out-
put.
Input Capacitor
Select a 2.2μF 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 volt-
age 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 coef-
ficient 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.
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.
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
2146.2008.10.1.2
www.analogictech.com
11
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet AAT2146.PDF ] | |
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