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Teilenummer | AAT1147 |
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Beschreibung | Step-Down Converter | |
Hersteller | AAT | |
Logo | ||
Gesamt 19 Seiten AAT1147
High Efficiency, Low Noise, Fast Transient
400mA Step-Down Converter
General Description
Features
SwitchReg™
The AAT1147 SwitchReg is a member of
AnalogicTech's Total Power Management IC™
(TPMIC™) product family. It is a fixed frequency
1.4MHz step-down converter with an input volt-
age range of 2.7V to 5.5V and output voltage as
low as 0.6V.
The AAT1147 is optimized for low noise portable
applications, reacts quickly to load variations, and
reaches peak efficiency at heavy load.
The AAT1147 output voltage is programmable with
external feedback resistors. It can deliver 400mA
of load current while maintaining high power effi-
ciency. The 1.4MHz switching frequency mini-
mizes the size of external components while keep-
ing switching losses low.
• VIN Range: 2.7V to 5.5V
• VOUT Adjustable from 0.6V to VIN
• 400mA Output Current
• Up to 98% Efficiency
• Low Noise, 1.4MHz Fixed Frequency PWM
Operation
• Fast Load Transient
• 150µs Soft Start
• Over-Temperature and Current Limit
Protection
• 100% Duty Cycle Low Dropout Operation
• <1µA Shutdown Current
• 8-Pin SC70JW Package
• Temperature Range: -40°C to +85°C
The AAT1147 is available in a Pb-free, space-sav-
ing 2.0x2.1mm SC70JW-8 package and is rated
Applications
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
VIN
C2
4.7μF
U1
AAT1147
3 VIN
LX 4
1 EN
OUT 2
5 AGND PGND 7
8 PGND PGND 6
VO = 1.8V
L1
4.7μH R1
118k
R2
59k
C1
4.7μF
1147.2006.05.1.0
1
AAT1147
High Efficiency, Low Noise, Fast Transient
400mA Step-Down Converter
Typical Characteristics
Line Regulation
(VOUT = 3.3V)
0.5
0.4
0.3
0.2 IOUT = 10mA IOUT = 1mA
0.1
0
-0.1
-0.2
-0.3 IOUT = 400mA
-0.4
-0.5
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
Input Voltage (V)
Line Regulation
(VOUT = 2.5V)
0.5
0.4
0.3
0.2 IOUT = 10mA IOUT = 1mA
0.1
0.0
-0.1
-0.2
-0.3 IOUT = 400mA
-0.4
-0.5
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
Input Voltage (V)
Line Regulation
(VOUT = 1.8V)
0.5
0.4
0.3
0.2
0.1 IOUT = 10mA IOUT = 1mA
0.0
-0.1
-0.2
-0.3
-0.4
IOUT = 400mA
-0.5
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
Input Voltage (V)
Frequency vs. Input Voltage
2.0
1.0
0.0 VOUT = 1.8V
-1.0
-2.0
VOUT = 2.5V VOUT = 3.3V
-3.0
-4.0
2.5 2.9 3.3 3.7 4.1 4.5 4.9 5.3
Input Voltage (V)
Output Voltage Error vs. Temperature
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-40 -25 -10
5
20 35 50 65 80 95
Temperature (°C)
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
15
12
9
6
3
0
-3
-6
-9
-12
-15
-40 -25 -10
5
20 35 50 65 80 95
Temperature (°C)
6 1147.2006.05.1.0
6 Page AAT1147
High Efficiency, Low Noise, Fast Transient
400mA Step-Down Converter
Figure 2: AAT1147 Evaluation Board
Top Side.
Figure 3: Exploded View of Evaluation
Board Top Side Layout.
Figure 4: AAT1147 Evaluation Board
Bottom Side.
The maximum output capacitor RMS ripple current
is given by:
I =RMS(MAX)
1
2·
·
3
VOUT · (VIN(MAX) - VOUT)
L · FS · VIN(MAX)
Dissipation due to the RMS current in the ceramic
output capacitor ESR is typically minimal, resulting in
less than a few degrees rise in hot-spot temperature.
Output Resistor Selection
The output voltage of the AAT1147 0.6V version can
be externally programmed. Resistors R1 and R2 of
Figure 5 program the output to regulate at a voltage
higher than 0.6V. To limit the bias current required for
the external feedback resistor string while maintain-
ing good noise immunity, the minimum suggested
value for R2 is 59kΩ. Although a larger value will fur-
ther reduce quiescent current, it will also increase
the impedance of the feedback node, making it more
sensitive to external noise and interference. Table 2
summarizes the resistor values for various output
voltages with R2 set to either 59kΩ for good noise
immunity or 221kΩ for reduced no load input current.
R1
=
⎛ VOUT
⎝ VREF
-1⎞⎠
·
R2
=
⎛ 1.5V
⎝ 0.6V
-
1⎞⎠
·
59kΩ
=
88.5kΩ
12 1147.2006.05.1.0
12 Page | ||
Seiten | Gesamt 19 Seiten | |
PDF Download | [ AAT1147 Schematic.PDF ] |
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