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AAT1147 Schematic ( PDF Datasheet ) - Skyworks

Teilenummer AAT1147
Beschreibung Fast Transient 400mA Step-Down Converter
Hersteller Skyworks
Logo Skyworks Logo 




Gesamt 18 Seiten
AAT1147 Datasheet, Funktion
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
General Description
The AAT1147 SwitchReg is a member of Skyworks' Total
Power Management IC™ (TPMIC™) product family. It is
a fixed frequency 1.4MHz step-down converter with an
input voltage range of 2.7V to 5.5V and output voltage
as low as 0.6V.
The AAT1147 is optimized for low noise portable applica-
tions, 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 efficiency. The
1.4MHz switching frequency minimizes the size of exter-
nal components while keeping switching losses low.
The AAT1147 is available in a 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
• 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
Applications
• Cellular Phones
• Digital Cameras
• 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
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
1






AAT1147 Datasheet, Funktion
DATA SHEET
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)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
6 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012

6 Page









AAT1147 pdf, datenblatt
DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
Since the inductance of a short PCB trace feeding the
input voltage is significantly lower than the power leads
from the bench power supply, most applications do not
exhibit this problem.
In applications where the input power source lead induc-
tance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or alu-
minum electrolytic should be placed in parallel with the
low ESR, ESL bypass ceramic. This dampens the high Q
network and stabilizes the system.
Output Capacitor
The output capacitor limits the output ripple and pro-
vides holdup during large load transitions. A 4.7μF to
10μF X5R or X7R ceramic capacitor typically provides
sufficient bulk capacitance to stabilize the output during
large load transitions and has the ESR and ESL charac-
teristics necessary for low output ripple.
The output voltage droop due to a load transient is dom-
inated by the capacitance of the ceramic output capacitor.
During a step increase in load current, the ceramic output
capacitor alone supplies the load current until the loop
responds. Within two or three switching cycles, the loop
responds and the inductor current increases to match the
load current demand. The relationship of the output volt-
age droop during the three switching cycles to the output
capacitance can be estimated by:
COUT
=
3 · ΔILOAD
VDROOP · FS
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equa-
tion establishes a limit on the minimum value for the
output capacitor with respect to load transients.
The internal voltage loop compensation also limits the
minimum output capacitor value to 4.7μF. This is due to
its effect on the loop crossover frequency (bandwidth),
phase margin, and gain margin. Increased output capac-
itance will reduce the crossover frequency with greater
phase margin.
The maximum output capacitor RMS ripple current is
given by:
I =RMS(MAX)
1
·
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 maintaining good noise
immunity, the minimum suggested value for R2 is 59k.
Although a larger value will further reduce quiescent cur-
rent, 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 59kfor
good noise immunity or 221kfor reduced no load input
current.
R1
=
VOUT
VREF
-1⎞⎠
·
R2
=
1.5V
0.6V
-
1⎞⎠
·
59kΩ
=
88.5kΩ
The AAT1147, combined with an external feedforward
capacitor (C4 in Figure 1), delivers enhanced transient
response for extreme pulsed load applications. The addi-
tion of the feedforward capacitor typically requires a
larger output capacitor C1 for stability.
VOUT (V)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
R2 = 59kΩ
R1 (kΩ)
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
R2 = 221kΩ
R1 (kΩ)
75
113
150
187
221
261
301
332
442
464
523
715
1000
Table 2: Resistor Values For Use With
0.6V Step-Down Converter.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
12 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012

12 Page





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