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AAT1112 Schematic ( PDF Datasheet ) - Advanced Analog Technology

Teilenummer AAT1112
Beschreibung Step-Down Converter
Hersteller Advanced Analog Technology
Logo Advanced Analog Technology Logo 




Gesamt 20 Seiten
AAT1112 Datasheet, Funktion
General Description
The AAT1112 SwitchReg is a 1.5A step-down con-
verter with an input voltage range of 2.4V to 5.5V
and an adjustable output voltage from 0.6V to VIN.
The 1.4MHz switching frequency enables the use
of small external components. The small footprint
and high efficiency make the AAT1112 an ideal
choice for portable applications.
The AAT1112 delivers 1.5A maximum output current
while consuming only 42µA of no-load quiescent
current. Ultra-low RDS(ON) integrated MOSFETs and
100% duty cycle operation make the AAT1112 an
ideal choice for high output voltage, high current
applications which require a low dropout threshold.
The AAT1112 provides excellent transient
response and high output accuracy across the
operating range. No external compensation com-
ponents are required.
The AAT1112 is designed to maintain high efficien-
cy throughout the load range. Pulling the MODE/
SYNC pin high enables "PWM Only" mode, main-
taining constant frequency and low output ripple
across the operating range. Alternatively, the con-
verter may be synchronized to an external clock
input via the MODE/SYNC pin. Over-temperature
and short-circuit protection safeguard the AAT1112
and system components from damage.
The AAT1112 is available in a Pb-free, space-sav-
ing TDFN33-12 or 2.75x3mm TSOPJW-12 pack-
age. The product is rated over an operating tem-
perature range of -40°C to +85°C.
AAT1112
1.5A, 1.4MHz Step-Down Converter
Features
SwitchReg
• 1.5A Maximum Output Current
• Input Voltage: 2.4V to 5.5V
• Output Voltage: 0.6V to VIN
• Up to 95% Efficiency
• 42µA No Load Quiescent Current
• No External Compensation Required
• 1.4MHz Switching Frequency
• Synchronizable to External Clock
• Optional "PWM Only" Low Noise Mode
• 100% Duty Cycle Low-Dropout Operation
• Internal Soft Start
• Over-Temperature and Current Limit
Protection
• <1µA Shutdown Current
• TSOPJW-12 or TDFN33-12 Package
• Temperature Range: -40°C to +85°C
Applications
• Cellular Phones
• Digital Cameras
• Hard Disk Drives
• MP3 Players
• PDAs and Handheld Computers
• Portable Media Players
• USB Devices
Typical Application
VIN
C2
10µF
VP LX
AAT1112
VIN
EN FB
MODE/SYNC
GND
PGND
L1
3.3µH
VOUT= 3.3V
R1
267kΩ
R2
59kΩ
C1
22µF
1112.2007.01.1.1
1






AAT1112 Datasheet, Funktion
AAT1112
1.5A, 1.4MHz Step-Down Converter
Typical Characteristics
Efficiency vs. Output Current
(PWM Mode; VOUT = 2.5V)
100
90
80
VIN = 2.7V
70
60
50 VIN = 5.0V
40
30 VIN = 4.2V
20
10 VIN = 3.6V
0
1 10 100
1000
Output Current (mA)
10000
Load Regulation
(PWM Mode; VOUT = 2.5V)
0.50
0.25 VIN = 2.7V
VIN = 3.6V
VIN = 5.0V
0.00
-0.25
VIN = 4.2V
-0.50
0.1
1 10 100 1000
Output Current (mA)
10000
Efficiency vs. Output Current
(PFM Mode; VOUT = 1.8V)
100
90 VIN = 2.7V
80
70 VIN = 3.6V VIN = 4.2V
60
50
40
0.1
1
10 100 1000
Output Current (mA)
10000
0.50
0.25
0.00
-0.25
-0.50
0.1
Load Regulation
(PFM Mode; VOUT = 1.8V)
VIN = 3.6V
VIN = 2.7V
VIN = 4.2V
1 10 100
Output Current (mA)
1000
100
90
80
70
60
50
40
30
20
10
0
1
Efficiency vs. Output Current
(PWM Mode; VOUT = 1.8V)
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V
10 100 1000
Output Current (mA)
10000
0.50
0.25
0.00
-0.25
-0.50
0.1
Load Regulation
(PWM Mode; VOUT = 1.8V)
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
1 10 100 1000
Output Current (mA)
10000
6 1112.2007.01.1.1

6 Page









AAT1112 pdf, datenblatt
AAT1112
1.5A, 1.4MHz Step-Down Converter
VIN
C1
10µF
3
2
1
Enable
3
2
1
SYNC
U1
AAT1112
TDFN33-12
11 VP
LX
12
7 VCC
N/C 4
8 EN
FB 6
9 SYNC PGND 3
10 N/C PGND 2
5 GND PGND 1
L1
3.3µH
R2
3.3V
C3
(optional)
C2
22µF
R3
59K
Figure 1: AAT1112 Schematic.
Component Selection
Inductor Selection
The step-down converter uses peak current mode
control with slope compensation to maintain stabil-
ity for duty cycles greater than 50%. The output
inductor value must be selected so the inductor
current down slope meets the internal slope com-
pensation requirements. The inductor should be
set equal to the output voltage numeric value in µH.
This guarantees that there is sufficient internal
slope compensation.
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 3.3µH CDRH4D28 series Sumida inductor has
a 49.2mΩ worst case DCR and a 1.57A DC current
rating. At full 1.5A load, the inductor DC loss is
97mW which gives less than 1.5% loss in efficien-
cy for a 1.5A, 3.3V output.
Input Capacitor
Select a 10µF to 22µF 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.
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
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.
12 1112.2007.01.1.1

12 Page





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