A7122AE6VR [AITSEMI]
DC-DC CONVERTER BUCK;
| 型号： | A7122AE6VR |
| 厂家： | 
AiT Semiconductor |
| 描述： | DC-DC CONVERTER BUCK DC-DC转换器 |
| 文件： | 总13页 (文件大小：496K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
DESCRIPTION
FEATURES
The A7122A is
a
high-efficiency, DC-to-DC
High Efficiency: Up to 97%
Capable of Delivering 2A
step-down switching regulators, capable of delivering
up to 2A of output current. The device operates from
an input voltage range of 2.5V to 5.5V and provides
an output voltage from 0.6V to VIN, making the
A7122A ideal for low voltage power conversions.
Running at a fixed frequency of 1.3MHz allows the
use of small external components, such as ceramic
input and output caps, as well as small inductors,
while still providing low output ripples. This low noise
output along with its excellent efficiency achieved by
the internal synchronous rectifier, making A7122A an
ideal green replacement for large power consuming
linear regulators. Internal soft-start control circuitry
1.3MHz Switching Frequency
No External Schottky Diode Needed
Light-load Mode
Internal Compensation and Soft-Start
Current Mode control
0.6V Reference for Low Output voltages
Logic Control Shutdown (IQ<1uA)
Thermal shutdown and UVLO
Available in SOT-26 and SOT-25 Packages
APPLICATION
Digital Cameras
reduces
inrush
current.
Short-circuit
and
MP3 and MP4 players
Set top boxes
thermal-overload protection improves design
reliability.
Wireless and DSL Modems
USB supplied Devices in Notebooks
Portable Devices
The A7122A is available in SOT-26 and SOT-25
packages.
TYPICAL APPLICATION
ORDERING INFORMATION
Package Type
SOT-26
Part Number
A7122AE6R
E6
E5
A7122AE6VR
A7122AE5R
A7122AE5VR
SOT-25
Note
V: Halogen free Package
R: Tape & Reel
SPQ: 3,000pcs/Reel
AiT provides all RoHS products
Suffix “ V “ means Halogen free Package
REV1.0
- MAY 2016 RELEASED -
- 1 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
PIN DESCRIPTION
Top View
Top View
Function
Pin #
Symbol
SOT-26
SOT-25
1
2
3
4
5
6
1
2
3
4
-
EN
GND
SW
IN
Enable pin
Ground
Power Switch Output
Power Supply Input
Not Connected
NC
FB
5
Feedback input pin
REV1.0
- MAY 2016 RELEASED -
- 2 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
ABSOLUTE MAXIMUM RATINGS
Max Input Voltage
6.5V
125°C
TJ, Max Operating Junction Temperature
TA, Ambient Temperature
Maximum Power Dissipation
TS, Storage Temperature
Lead Temperature & Time
-40°C ~ 85°C
400mW
SOT-25
-40°C ~ 150°C
260°C, 10s
Stress beyond above listed “Absolute Maximum Ratings” may lead permanent damage to the device. These are stress ratings only and
operations of the device at these or any other conditions beyond those indicated in the operational sections of the specifications are not
implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING CONDITIONS
Parameter
VIN Supply Voltage
Operating Temperature
Symbol
VIN
Min
2.5
-40
Max
5.5
85
Unit
V
TOPT
℃
REV1.0
- MAY 2016 RELEASED -
- 3 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
ELECTRICAL CHARACTERISTICS
VDD=5V, TA=25°C
Parameter
Input Voltage Range
Feedback Voltage
Feedback Leakage Current
Quiescent Current
Shutdown Current
Switching Frequency
PMOSFET RDSON
Symbol
VIN
Conditions
Min.
2.5
Typ.
Max.
5.5
Unit
V
VFB
0.585
0.6
0.1
50
0.615
0.4
V
IFB
μA
μA
μA
MHz
mΩ
mΩ
A
IQ
Active, VFB=0.65V
Shutdown
ISD
1
FSW
RONP
RONN
ILIMIT
1.3
120
80
NMOSFET RDSON
Peak Current Limit
2.5
1.5
VIN=5.5V,VSW=0 or 5.5V,
VEN=0V
SW Leakage Current
ISW
10
1
μA
EN Leakage Current
IEN
VENH
μA
V
EN Input High Voltage
EN Input Low Voltage
Thermal Shutdown
VENL
0.4
V
TSD
150
15
℃
℃
Thermal Shutdown Hysteresis
HYSTSD
REV1.0
- MAY 2016 RELEASED -
- 4 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
TYPICAL OPERATING CHARACTERISTICS
Tested under TA=25°C, unless otherwise specified
1.
2.
4.
6.
3.
5.
REV1.0
- MAY 2016 RELEASED -
- 5 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
7.
8.
9.
10.
REV1.0
- MAY 2016 RELEASED -
- 6 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
BLOCK DIAGRAM
REV1.0
- MAY 2016 RELEASED -
- 7 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
DETAILED INFORMATION
Operation Description
The A7122A high-efficiency switching regulator is a small, simple, DC-to-DC step-down converter capable of
delivering up to 2A of output current. The device operates in pulse-width modulation (PWM) at 1.3MHz from a
2.5V to 5.5V input voltage and provides an output voltage from 0.6V on, making the A7122A ideal for
on-board post-regulation applications. An internal synchronous rectifier improves efficiency and eliminates the
typical Schottky free-wheeling diode. Using the on resistance of the internal high-side MOSFET to sense
switching currents eliminates current-sense resistors, further improving efficiency and cost.
Loop Operation
A7122A uses a PWM current-mode control scheme. An open-loop comparator compares the integrated
voltage-feedback signal against the sum of the amplified current-sense signal and the slope compensation
ramp. At each rising edge of the internal clock, the internal high-side MOSFET turns on until the PWM
comparator terminates the on cycle. During this on-time, current ramps up through the inductor, sourcing
current to the output and storing energy in the inductor. The current mode feedback system regulates the
peak inductor current as a function of the output voltage error signal. During the off cycle, the internal
high-side P-channel MOSFET turns off, and the internal low-side N-channel MOSFET turns on. The inductor
releases the stored energy as its current ramps down while still providing current to the output.
Current Sense
An internal current-sense amplifier senses the current through the high-side MOSFET during on time and
produces a proportional current signal, which is used to sum with the slope compensation signal. The
summed signal then is compared with the error amplifier output by the PWM comparator to terminate the on
cycle.
Current Limit
There is a cycle-by-cycle current limit on the high-side MOSFET of 2.5A. When the current flowing out of SW
exceeds this limit, the high-side MOSFET turns off and the synchronous rectifier turns on. A7122A utilizes a
frequency fold-back mode to prevent overheating during short-circuit output conditions. The device enters
frequency fold-back mode when the FB voltage drops below 200mV, limiting the current to 2.5A and reducing
power dissipation. Normal operation resumes upon removal of the short-circuit condition.
REV1.0
- MAY 2016 RELEASED -
- 8 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
Soft-start
A7122A has a internal soft-start circuitry to reduce supply inrush current during startup conditions. When the
device exits under-voltage lockout (UVLO), shutdown mode, or restarts following a thermal-overload event,
the l soft-start circuitry slowly ramps up current available at SW.
UVLO and Thermal Shutdown
If IN drops below 2.5V, the UVLO circuit inhibits switching. Once IN rises above 2.5V, the UVLO clears, and
the soft-start sequence activates. Thermal-overload protection limits total power dissipation in the device.
When the junction temperature exceeds TJ= +150°C, a thermal sensor forces the device into shutdown,
allowing the die to cool. The thermal sensor turns the device on again after the junction temperature cools by
15°C, resulting in a pulsed output during continuous overload conditions. Following a thermal-shutdown
condition, the soft-start sequence begins.
Application Information
Setting Output Voltages
Output voltages are set by external resistors. The FB_ threshold is 0.6V.
RTOP = RBOT [(VOUT / 0.6) - 1]
Input Capacitor Selection
The input capacitor in a DC-to-DC converter reduces current peaks drawn from the battery or other input
power source and reduces switching noise in the controller. The impedance of the input capacitor at the
switching frequency should be less than that of the input source so high-frequency switching currents do not
pass through the input source. The output capacitor keeps output ripple small and ensures control-loop
stability. The output capacitor must also have low impedance at the switching frequency. Ceramic, polymer,
and tantalum capacitors are suitable, with ceramic exhibiting the lowest ESR and high-frequency impedance.
Output ripple with a ceramic output capacitor is approximately as follows:
VRIPPLE = IL(PEAK)[1 / (2π x fOSC x COUT)]
If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows:
VRIPPLE(ESR) = IL(PEAK) x ESR
REV1.0
- MAY 2016 RELEASED -
- 9 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
Output Capacitor and Inductor Selection
Follow the below table for Inductor and Output cap selection:
VOUT
COUT
L
1.2V
33μF
1.5μH
1.5V
33μF
1.5μH
1.8V
22μF
2.2μH
2.5V
3.3V
10μF
4.7μH
22μF
3.3μH
If much smaller values are used, inductor current rises, and a larger output capacitance may be required to
suppress output ripple. Larger values than LIDEAL can be used to obtain higher output current, but typically
with larger inductor size.
Layout Guideline
Layout is critical to achieve clean and stable operation. The switching power stage requires particular
attention. Follow these guidelines for good PC board layout:
1.
2.
Place decoupling capacitors as close to the IC as possible
Connect input and output capacitors to the same power ground node with a star ground configuration
then to IC ground.
3.
4.
Keep the high-current paths as short and wide as possible. Keep the path of switching current (C1 to IN
and C1 to GND) short. Avoid vias in the switching paths.
If possible, connect IN, SW, and GND separately to a large copper area to help cool the IC to further
improve efficiency and long-term reliability.
5.
6.
Ensure all feedback connections are short and direct. Place the feedback resistors as close to the IC as
possible.
Route high-speed switching nodes away from sensitive analog area.
REV1.0
- MAY 2016 RELEASED -
- 10 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
PACKAGE INFORMATION
Dimension in SOT-26 (Unit: mm)
Symbol
Millimeters
Inches
Min
Max
Min
Max
A
A1
A2
b
1.050
0.000
1.050
0.300
0.100
2.820
1.500
2.650
1.250
0.100
1.150
0.400
0.200
3.020
1.700
2.950
0.041
0.000
0.041
0.012
0.004
0.111
0.059
0.104
0.049
0.004
0.045
0.016
0.008
0.119
0.067
0.116
c
D
E
E1
e
0.950TYP
0.700REF
0.037TYP
0.028REF
e1
L
1.800
2.000
0.071
0.079
L1
θ
0.300
0°
0.600
8°
0.012
0°
0.024
8°
REV1.0
- MAY 2016 RELEASED -
- 11 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
Dimension in SOT-25 (Unit: mm)
REV1.0
- MAY 2016 RELEASED -
- 12 -
A7122A
DC-DC CONVERTER BUCK (STEP-DOWN)
5.5V 2A 1.3MHz SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
IMPORTANT NOTICE
AiT Semiconductor Inc. (AiT) reserves the right to make changes to any its product, specifications, to
discontinue any integrated circuit product or service without notice, and advises its customers to obtain the
latest version of relevant information to verify, before placing orders, that the information being relied on is
current.
AiT Semiconductor Inc.'s integrated circuit products are not designed, intended, authorized, or warranted to
be suitable for use in life support applications, devices or systems or other critical applications. Use of AiT
products in such applications is understood to be fully at the risk of the customer. As used herein may involve
potential risks of death, personal injury, or servere property, or environmental damage. In order to minimize
risks associated with the customer's applications, the customer should provide adequate design and
operating safeguards.
AiT Semiconductor Inc. assumes to no liability to customer product design or application support. AiT
warrants the performance of its products of the specifications applicable at the time of sale.
REV1.0
- MAY 2016 RELEASED -
- 13 -
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