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PDF AAT1276 Data sheet ( Hoja de datos )
| Número de pieza | AAT1276 | |
| Descripción | Boost Converter | |
| Fabricantes | Advanced Analogic Technologies | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AAT1276 (archivo pdf) en la parte inferior de esta página. Total 18 Páginas | ||
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SwitchRegTM
PRODUCT DATASHEET
AAT1276
Boost Converter with USB Power Switch
General Description
The AAT1276 SwitchReg is a 2MHz, 500mA synchronous
boost converter with an integrated current-limiting load
switch controlled output. The AAT1276 operates from a
single-cell Lithium-ion/ polymer battery source and pro-
vides a regulated 5V, current limit controlled output to
support USB port VBUS applications in portable consumer
electronic products. The AAT1276 can support both USB
2.0 host port and USB on-the-go operation, as well as
www.DatagSeheneet4raUl.cpomurpose applications where a 5V supply with a
user programmable current limit is needed.
The high efficiency boost converter section of the
AAT1276 is typically set for a 5V output and can deliver
up to 500mA load current to support USB VBUS operation
from an input supply as low as 2.7V. The high boost
converter switching frequency (up to 2.0MHz) provides
fast load transient and allows the use of small external
components. Fully integrated control circuitry simplifies
system design and reduces total solution size.
The integrated, programmable current limiting load
switch provides USB port protection for portable devices
allowing the AAT1276 to supply a 5V USB VBUS up to
500mA. The load switch provides an active low fault flag
to alert the system in the event of an over-current condi-
tion applied to the AAT1276 output.
The AAT1276 is available in the Pb-free, space-saving
12-pin TSOPJW and 16-pin TDFN34 packages and is
rated over the -40°C to +85°C operating temperature
range.
Typical Application
Features
• High Frequency Boost With 5V / 500mA Output Capability
From a Single-Cell Lithium-Ion/Polymer Battery
• Input Voltage Range: 2.7V to 5V
• VOUT1 Adjustable or Fixed (5V)
• >90% Efficiency
• Up to 2MHz Switching Frequency
• True Load Disconnect
• Load Switch With Programmable Current Limit
• Over-Temperature, Over-Current Protection
• Inrush Current Limit
• Fault Report
• Low Shutdown Current < 1μA Typical
• -40°C to +85°C Temperature Range
• TSOPJW-12 and TDFN34-16 Packages
Applications
• USB On-the-Go
• Cell Phones
• Digital Still Cameras
• PDAs and Portable Media Players
• Smart Phones
• Other Hand-Held Devices
VIN
Fault
Enable
CIN
4.7μF
10k
RSET
L1 2.2μH
LIN
IN
SW
OUT1
VCC
FB
AAT1276
FLT
EN
OUT2
SET
GND
RFB1
432k
RFB2
59k
COUT1
4.7μF
COUT2
1μF
VBUS Output
1276.2007.11.1.1
www.analogictech.com
1
1 page  
SwitchRegTM
Typical Characteristics
Efficiency vs. Load
100
80
60
40
www.DataSheet4U.com
20
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V
0
0.1 1
10 100
Output Current (mA)
1000
Line Regulation
(IOUT = 300mA)
4.960
4.958
4.956
4.954
4.952
4.950
4.948
4.946
4.944
4.942
4.940
3.6 3.7 3.8 3.9 4.0 4.1 4.2
Input Voltage (V)
No Load Current vs. Supply Voltage
140
120
85°C
100
80
60
-40°C
25°C
40
20
0
2.7 2.9 3.2 3.4 3.6 3.9 4.1 4.3 4.5 4.8 5.0
Supply Voltage (V)
PRODUCT DATASHEET
AAT1276
Boost Converter with USB Power Switch
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
0.1
DC Regulation
(VOUT = 5.0V)
VIN = 4.2V
VIN = 2.7V VIN = 3.6V
1 10 100
Output Current (mA)
1000
Output Voltage vs. Temperature
(VIN = 3.6V; 50Ω Load)
0.1
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-50
-25
0
25 50 75
Temperature (°C)
100
No Load Current vs. Temperature
(VIN = 3.6V; VOUT = 5.0V)
140
120
100
80
60
40
20
0
-50
0
50 100
Temperature (°C)
150
1276.2007.11.1.1
www.analogictech.com
5
5 Page 
SwitchRegTM
Selecting the Boost Inductor
The AAT1276 boost controller utilizes hysteretic control
and the switching frequency varies with output load and
input voltage. The value of the inductor determines the
maximum switching frequency of the boost converter.
Increasing output inductance decreases the switching
frequency, resulting in higher peak currents and
increased output voltage ripple. To maintain the 2MHz
switching frequency and stable operation, an output
www.DataSinhdeuetc4tUo.rcomsized from 1.5μH to 2.7μH is recommended.
Manufacturer’s specifications list both the inductor DC
current rating, which is a thermal limitation, and peak
inductor current rating, which is a function of the satu-
ration characteristics.
Measure the inductor current at full load and high ambi-
ent temperature to ensure that the inductor does not
saturate or exhibit excessive temperature rise. Select
the output inductor (L) to avoid saturation at the mini-
mum input voltage and maximum load. The RMS current
flowing through the boost inductor is equal to the DC
plus AC ripple components. The maximum inductor RMS
current occurs at the minimum input voltage and the
maximum load. Use the following equations to calculate
the maximum peak and RMS current:
DMAX
= VO
-
VIN(MIN)
VO
IPP
=
VIN(MIN) · D
L · FS
IP
=
IO
1-D
IPK = IP +
IPP
2
IV = IP - IPP
IRMS =
IPK2 + IPK · IV + IV2
3
PLOSS(INDUCTOR) = I2RMS · DCR
At light load and low output voltage, the controller
reduces the operating frequency to maintain maximum
efficiency. As a result, further reduction in output load
does not reduce the peak current. The minimum peak
current ranges from 0.5A to 0.75A.
PRODUCT DATASHEET
AAT1276
Boost Converter with USB Power Switch
Compare the RMS current values with the manufactur-
er’s temperature rise, or thermal derating guidelines. For
a given inductor type, smaller inductor size leads to an
increase in DCR winding resistance and, in most cases,
increased thermal impedance. Winding resistance
degrades boost converter efficiency and increases the
inductor’s operating temperature.
Shielded inductors provide decreased EMI and may be
required in noise sensitive applications. Unshielded chip
inductors provide significant space savings at a reduced
cost compared to shielded inductors. In general, chip-
type inductors have increased winding resistance (DCR)
when compared to shielded, wound varieties.
Selecting the Step-Up Converter
Capacitors
The high output ripple inherent in the boost converter
necessitates low impedance output filtering. Multi-layer
ceramic (MLC) capacitors provide small size, adequate
capacitance, with low parasitic equivalent series resis-
tance (ESR) and equivalent series inductance (ESL). This
makes them well suited for use with the AAT1276. MLC
capacitors of type X7R or X5R ensure good capacitance
stability over the full operating range. MLC capacitors
exhibit significant capacitance reduction with an applied
DC voltage. Output ripple measurements can confirm
that the capacitance used meets the specific ripple
requirements. Voltage derating minimizes this factor, but
results may vary with package size and among specific
manufacturers.
Use a 4.7μF 10V ceramic output capacitor to minimize
output ripple for the 5V output. Small 0805 sized ceram-
ic capacitors are available which meet these require-
ments.
Estimate the output capacitor required at the minimum
switching frequency (FS) of 800kHz (worst-case).
COUT =
IOUT · DMAX
FS · ΔVOUT
The boost converter input current flows during both ON
and OFF switching intervals. The input ripple current is
less than the output ripple and, as a result, less input
capacitance is required. A ceramic output capacitor from
1μF to 4.7μF is recommended. Minimum 6.3V rated
capacitors are required at the input. Ceramic capacitors
sized as small as 0603 are available which meet these
requirements.
1276.2007.11.1.1
www.analogictech.com
11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet AAT1276.PDF ] | |
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