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PDF AAT1146 Data sheet ( Hoja de datos )
| Número de pieza | AAT1146 | |
| Descripción | Step-Down Converter | |
| Fabricantes | AAT | |
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AAT1146
Fast Transient 400mA Step-Down Converter
General Description
Features
SwitchReg™
The AAT1146 SwitchReg is a member of
AnalogicTech's Total Power Management IC™
(TPMIC™) product family. It is a 1.4MHz 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 AAT1146 is available in fixed voltage versions
with internal feedback and a programmable ver-
sion with external feedback resistors. It can deliver
400mA of load current while maintaining a low
27μA no load quiescent current. The 1.4MHz
switching frequency minimizes the size of external
components while keeping switching losses low.
The AAT1146 is designed to maintain high efficien-
cy throughout the operating range, which is critical
for portable applications.
• VIN Range: 2.7V to 5.5V
• VOUT Fixed or Adjustable from 0.6V to VIN
• 27μA No Load Quiescent Current
• Up to 98% Efficiency
• 400mA 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
• SC70JW-8 Package
• Temperature Range: -40°C to +85°C
The AAT1146 is available in a Pb-free, space-saving
Applications
2.0x2.1mm SC70JW-8 package and is rated over
the -40°C to +85°C temperature range.
• Cellular Phones
• Digital Cameras
•www.DataSheet4U.com Handheld Instruments
• Microprocessor / DSP Core / IO Power
• PDAs and Handheld Computers
• USB Devices
Typical Application (Fixed Output Voltage)
VIN
C2
4.7μF
U1
AAT1146
3 VIN
LX 4
1 EN
OUT 2
5 AGND PGND 7
8 PGND PGND 6
L1
4.7μH
VO
C1
4.7μF
1146.2006.04.1.3
1
1 page  
AAT1146
Fast Transient 400mA Step-Down Converter
Typical Characteristics
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
1.0
0.5
0.0
-0.5
-1.0
0.1
DC Regulation
(VOUT = 1.8V)
VIN = 4.2V
VIN = 3.6V
VIN = 2.7V
1 10 100 1000
Output Current (mA)
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
1.0
0.5
0.0
-0.5
-1.0
0.1
DC Regulation
(VOUT = 2.5V)
VIN = 4.2V
VIN = 5.0V
VIN = 3.6V
VIN = 3.0V
1 10 100
Output Current (mA)
1000
Efficiency vs. Load
(VOUT = 3.3V; L = 6.8μH)
100
VIN = 3.6V
90
VIN = 4.2V
80
VIN = 5.0V
70
60
1.0
0.5
0.0
-0.5
50
0.1
-1.0
1 10 100 1000
0.1
Output Current (mA)
DC Regulation
(VOUT = 3.3V; L = 6.8µH)
VIN = 5.0V
VIN = 4.2V
VIN = 3.6V
1 10 100
Output Current (mA)
1000
1146.2006.04.1.3
5
5 Page 
AAT1146
Fast Transient 400mA Step-Down Converter
Applications Information
Inductor Selection
The step-down converter uses peak current mode
control with slope compensation to maintain stability
for duty cycles greater than 50%. The output induc-
tor 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
AAT1146 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
adjustable (0.6V) version or low-voltage fixed ver-
sions. When externally programming the 0.6V ver-
sion 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
= 3μsAec ⋅ 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
AAT1146 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
saturation 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 loss-
es 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 rating. At full load, the inductor DC loss is
17mW which gives a 2.8% loss in efficiency for a
400mA, 1.5V output.
Input Capacitor
Select a 4.7μF to 10μF X7R or X5R ceramic capac-
itor for the input. To estimate the required input
capacitor size, determine the acceptable input rip-
ple level (VPP) and solve for C. The calculated
value varies with input voltage and is a maximum
when VIN is double the output voltage.
VO
VIN
·
⎛⎝1 -
VO ⎞
VIN ⎠
CIN =
⎛ VPP
⎝ IO
- ESR⎞⎠ · FS
VO
VIN
·
⎛⎝1 -
VO ⎞
VIN ⎠
=
1
4
for
VIN
=
2
×
VO
1
CIN(MIN) = ⎛ VPP
⎝ IO
- ESR⎞⎠ · 4 · FS
Always examine the ceramic capacitor DC voltage
coefficient characteristics when selecting the prop-
er 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
Table 1: Inductor Values.
Inductor
2.2μH
4.7μH
6.8μH
4.7μH
1146.2006.04.1.3
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet AAT1146.PDF ] | |
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