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PDF AAT2158 Data sheet ( Hoja de datos )
| Número de pieza | AAT2158 | |
| Descripción | 1.5A Low Noise Step-Down Converter | |
| Fabricantes | Advanced Analogic Technologies | |
| Logotipo |  |
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SwitchRegTM
www.DataSheet4U.com
General Description
The AAT2158 SwitchReg is a 1.5A step-down converter
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 AAT2158 an ideal choice for portable applications.
The AAT2158 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 AAT2158 an ideal choice for
high output voltage, high current applications which
require a low dropout threshold.
The AAT2158 provides excellent transient response and
high output accuracy across the operating range. No
external compensation components are required.
The AAT2158 maintains high efficiency throughout the
load range. The AAT2158’s unique architecture produces
reduced ripple and spectral noise. Over-temperature and
short-circuit protection safeguard the AAT2158 and sys-
tem components from damage.
The AAT2158 is available in a Pb-free, space-saving
16-pin 3x3mm QFN package. The product is rated over
an operating temperature range of -40°C to +85°C.
PRODUCT DATASHEET
AAT2158
1.5A Low Noise Step-Down Converter
Features
• 1.5A Maximum Output Current
• Input Voltage: 2.4V to 5.5V
• Output Voltage: 0.6V to VIN
• Up to 95% Efficiency
• Low Noise Light Load Mode
• 42µA No Load Quiescent Current
• No External Compensation Required
• 1.4MHz Switching Frequency
• 100% Duty Cycle Low-Dropout Operation
• Internal Soft Start
• Over-Temperature and Current Limit Protection
• <1µA Shutdown Current
• 16-Pin 3x3mm QFN 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
3.3V
C1
10µF
U1
AAT2158
12 VP
FB 4
11 VP
LX 15
10 VP
LX 14
7 EN
LX 13
9 VCC
N/C 16
6 N/C PGND 3
8 N/C PGND 2
5 SGND PGND 1
L1
2.2µH
2.5V
R3
187k
R4
59k
C3
22µF
2158.2008.10.1.5
www.analogictech.com
1
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SwitchRegTM
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Typical Characteristics
Efficiency vs. Output Current
(VOUT = 3.3V)
100
90
80
70 VIN = 4.2V VIN = 5.0V
60 VIN = 3.6V
50
40
30
0 1 10 100 1000
Output Current (mA)
10000
Efficiency vs. Output Current
(VOUT = 1.8V)
100
90 VIN = 2.7V
80
70
VIN = 3.6V
VIN = 4.2V
60
50
40
30
0
1 10 100 1000
Output Current (mA)
10000
Efficiency vs. Output Current
(VOUT = 1.2V)
100
90 VIN = 2.7V
80
70
60
VIN = 3.6V
VIN = 4.2V
50
40
30
0 1 10 100 1000
Output Current (mA)
10000
PRODUCT DATASHEET
AAT2158
1.5A Low Noise Step-Down Converter
Load Regulation
(VOUT = 3.3V)
1.00
0.75 VIN = 5.0V
0.50
0.25 VIN = 4.2V
0.00
-0.25
-0.50 VIN = 3.6V
-0.75
-1.00
0.1
1
10 100
1000
Output Current (mA)
10000
1.00
0.75
0.50
0.25
0.00
-0.25
-0.50
-0.75
-1.00
0.1
Load Regulation
(VOUT = 1.8V)
VIN = 4.2V
VIN = 3.6V
VIN = 2.7V
1 10 100 1000
Output Current (mA)
10000
1.00
0.75
0.50
0.25
0.00
-0.25
-0.50
-0.75
-1.00
0.1
Load Regulation
(VOUT = 1.2V)
VIN = 4.2V
VIN = 2.7V
VIN = 3.6V
1 10 100
Output Current (mA)
1000
10000
2158.2008.10.1.5
www.analogictech.com
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SwitchRegTM
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Component Selection
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 inductor should be set equal to the output voltage
numeric value in µH. This guarantees that there is suf-
ficient 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 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 3.3µH CDRH4D28 series Sumida inductor has a
49.2mW 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 efficiency for a 1.5A, 3.3V
output.
Input Capacitor
Select a 10µF to 22µF 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.
VO · 1 - VO
VIN 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
PRODUCT DATASHEET
AAT2158
1.5A Low Noise Step-Down Converter
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.
The maximum input capacitor RMS current is:
IRMS = IO ·
VO · 1 - VO
VIN 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 · 1 - VO = D · (1 - D) = 0.52 = 1
VIN VIN
2
for VIN = 2 · VO
I =RMS(MAX)
IO
2
The
term
VO · 1 -
VIN
VO
VIN
appears
in
both
the
input
voltage
ripple and input capacitor RMS current equations and is
a maximum when VO is twice VIN. This is why the input
voltage ripple and the input capacitor RMS current ripple
are a maximum at 50% duty cycle.
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT2158. Low
ESR/ESL X7R and X5R ceramic capacitors are ideal for
this function. To minimize stray inductance, the capaci-
tor should be placed as closely as possible to the IC. This
keeps the high frequency content of the input current
localized, minimizing EMI and input voltage ripple.
The proper placement of the input capacitor (C1) can be
seen in the evaluation board layout in the Layout section
of this datasheet (see Figure 2).
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the eval-
uation board input voltage pins. The inductance of these
wires, along with the low-ESR ceramic input capacitor,
can create a high Q network that may affect converter
performance. This problem often becomes apparent in
the form of excessive ringing in the output voltage dur-
ing load transients. Errors in the loop phase and gain
measurements can also result.
2158.2008.10.1.5
www.analogictech.com
11
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| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet AAT2158.PDF ] | |
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