A7222E6R [AITSEMI]
DC-DC CONVERTER BUCK SYNCHRONOUS;
| 型号： | A7222E6R |
| 厂家： | 
AiT Semiconductor |
| 描述： | DC-DC CONVERTER BUCK SYNCHRONOUS DC-DC转换器 |
| 文件： | 总13页 (文件大小：652K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
DESCRIPTION
FEATURES
The A7222 is a fully integrated, high-efficiency 2A
synchronous rectified step-down converter. The
A7222 operates at high efficiency over a wide
output current load range.
High Efficiency: Up to 96%
500kHz Frequency Operation
2A Output Current
No Schottky Diode Required
This device offers two operation modes, PWM
control and PFM Mode switching control, which
allows a high efficiency over the wider range of the
load.
4.2V to 18V Input Voltage Range
0.8V Reference
Slope Compensated Current Mode Control for
Excellent Line and Load Transient Response
Integrated internal compensation
Stable with Low ESR Ceramic Output
Capacitors
The A7222 is available in SOT-26 package.
Over Current Protection with Hiccup-Mode
Thermal Shutdown
ORDERING INFORMATION
Inrush Current Limit and Soft Start
-40°C to +85°C Temperature Range
Available in SOT-26 Package
Package Type
Part Number
A7222E6R
A7222E6VR
SOT-26
SPQ: 3,000pcs/Reel
E6
V: Halogen free Package
R: Tape & Reel
APPLICATION
Note
Distributed Power Systems
AiT provides all RoHS products
Digital Set Top Boxes
Flat Panel Television and Monitors
Wireless and DSL Modems
Notebook Computer
TYPICAL APPLICATION
Figure 1.
Figure 2.
NOTE1: C1 and C2 recommended using 22uF ceramic capacitors. If the electrolytic capacitor is used, it is recommended that the ceramic
capacitor in parallel with a capacitance value of 2.2uF or more.
NOTE2: The resistance R3 in Figure 1 makes the loop more stable that recommended not exceed 20kΩ. If it isn’t used, the resistance
R1、R2 should be adjusted(See Figure2.). The value of R1 is recommended to be about 300kΩ.
REV1.0
- SEP 2016 RELEASED -
- 1 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
PIN DESCRIPTION
Top View
Pin #
Symbol
GND
SW
Function
1
2
3
Ground
Switching Pin
VIN
Power supply Pin
Adjustable version feedback input. Connect FB to the center point of
the external resistor divider.
4
5
6
FB
EN
Drive this pin to a logic-high to enable the IC. Drive to a logic-low to
disable the IC and enter micro-power shutdown mode.
Boostrap. A capacitor connected between SW and BST pins is
required to form a floating supply across the high-side switch driver.
BST
REV1.0
- SEP 2016 RELEASED -
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A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
ABSOLUTE MAXIMUM RATINGS
VIN, Supply Voltage
-0.3V ~ 19V
-0.3V ~ (VIN+0.5V)
VSW-0.3V ~ VSW+5V
-0.3V ~ 19V
VSW, Switch Node Voltage
VBST, Boost Voltage
VEN, Enable Voltage
All Other Pins
-0.3V ~ 6V
Operating Temperature Range
Storage Temperature Range
Lead Temperature (Soldering, 10s)
-40°C ~ 85°C
-65°C ~ 150°C
300°C
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.
ELECTRICAL CHARACTERISTICS
VIN=12V, VOUT=5V, TA=25°C, unless otherwise stated
Parameter
Conditions
Min.
4.2
Typ.
Max.
18
Unit
V
Input Voltage Range
UVLO Threshold
4.1
0.8
V
Supply Current in Operation
Supply Current in Shutdown
Regulated Feedback Voltage
High-side Switch On Resistance
Low-side Switch On Resistance
VEN = 2.0V, VFB = 1.1V
VEN = 0V or VEN = GND
4.2V≤VIN ≤18V
mA
μA
V
1
0.776
0.8
90
0.824
mΩ
mΩ
μA
A
70
High-side Switch Leakage Current VEN = 0V, VSW = 0V
0
10
Upper Switch Current Limit
Oscillation Frequency
Maximum Duty Cycle
Minimum On Time
Minimum Duty Cycle
3.8
500
92
kHz
%
VFB = 0.7V
100
160
ns
Thermal Shutdown
°C
REV1.0
- SEP 2016 RELEASED -
- 3 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
TYPICAL PERFORMANCE CHARACTERISTICS
Tested under, L=4.7uH, TA=25°C, unless otherwise specified
1.
3.
5.
Efficiency vs. IOUT(VOUT=1.2V)
Efficiency vs. IOUT(VOUT=5.0V)
VOUT vs. IOUT(VOUT=3.3V)
2.
4.
6.
Efficiency vs. IOUT(VOUT=3.3V)
VOUT vs. IOUT(VOUT=1.2V)
VOUT vs. IOUT(VOUT=5.0V)
REV1.0
- SEP 2016 RELEASED -
- 4 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
7.
Efficiency vs. VIN(IOUT=1A)
8.
VOUT vs. VIN(IOUT=1A)
9.
Load Transient
10. Load Transient
VIN =12V, VOUT =3.3V, IOUT =0.5~1A
Ch2—VOUT, Ch4--IL
VIN=12V, VOUT=3.3V, IOUT=0.01~2A
Ch2—VOUT, Ch4--IL
REV1.0
- SEP 2016 RELEASED -
- 5 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
BLOCK DIAGRAM
REV1.0
- SEP 2016 RELEASED -
- 6 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
DETAILED INFORMATION
Internal Regulator
The A7222 is a current mode step down DC/DC converter that provides excellent transient response with no
extra external compensation components. This device contains an internal, low resistance, high voltage
power MOSFET, and operates at a high 500K operating frequency to ensure a compact, high efficiency
design with excellent AC and DC performance.
Error Amplifier
The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a current
proportional to the difference between the two. This output current is then used to charge or discharge the
internal compensation network to form the COMP voltage, which is used to control the power MOSFET
current. The optimized internal compensation network minimizes the external component counts and
simplifies the control loop design.
Internal Soft-Start
The soft-start is implemented to prevent the converter output voltage from overshooting during startup. When
the chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 1.2V. When it is
lower than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference.
When SS is higher than REF, REF regains control. The SS time is internally fixed to 1ms.
Over-Current-Protection and Hiccup
The A7222 has a cycle-by-cycle over-current limit for when the inductor current peak value exceeds the set
current-limit threshold. First, when the output voltage drops until FB falls below the Under-Voltage (UV)
threshold (typically 140mV) to trigger a UV event, the A7222 enters hiccup mode to periodically restart the
part. This protection mode is especially useful when the output is dead-shorted to ground. This greatly
reduces the average short-circuit current to alleviate thermal issues and to protect the regulator. The A7222
exits hiccup mode once the overcurrent condition is removed.
Startup and Shutdown
If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block starts first,
generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator
provides stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low and
thermal shutdown. In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering.
The COMP voltage and the internal supply rail are then pulled down. The floating driver is not subject to this
shutdown command.
REV1.0
- SEP 2016 RELEASED -
- 7 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
Applications Information
Setting Output Voltages
The external resistor divider is used to set the output voltage (see Typical Application on page 1). The
feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor. Choose
R1 to be around 300kΩ for optimal transient response. R2 is then given by:
R2=
Selecting the Inductor
Use a 2.2μH-to-10μH inductor with a DC current rating of at least 25% percent higher than the maximum load
current for most applications. For highest efficiency, select an inductor with a DC resistance less than 15mΩ.
For most designs, derive the inductance value from the following equation.
L=
Where ΔIL is the inductor ripple current. Choose an inductor current approximately 30% of the maximum load
current. The maximum inductor peak current is:
IL(MAX) = ILOAD +
Under light-load conditions (below 100mA), use a larger inductor to improve efficiency.
Selecting the Output Capacitor
The output capacitor (C2) maintains the DC output voltage. Use ceramic, tantalum, or low-ESR electrolytic
capacitors. Use low ESR capacitors to limit the output voltage ripple. Estimate the output voltage ripple with:
ΔVOUT
=
Where L is the inductor value and RESR is the equivalent series resistance (ESR) of the output capacitor.
For ceramic capacitors, the capacitance dominates the impedance at the switching frequency and causes
most of the output voltage ripple. For simplification, estimate the output voltage ripple with:
ΔVOUT
=
For tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For
simplification, the output ripple can be approximated with:
ΔVOUT
=
REV1.0
- SEP 2016 RELEASED -
- 8 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
The characteristics of the output capacitor also affect the stability of the regulation system. The A7222 can be
optimized for a wide range of capacitance and ESR values.
PC BOARD LAYOUT
PCB layout is very important to achieve stable operation. For best results, use the following guidelines and
figures as reference.
1. Keep the connection between the input ground and GND pin as short and wide as possible.
2. Keep the connection between the input capacitor and VIN pin as short and wide as possible.
3. Use short and direct feedback connections. Place the feedback resistors and compensation components
as close to the chip as possible.
4. Route SW away from sensitive analog areas such as FB.
REV1.0
- SEP 2016 RELEASED -
- 9 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
TYPICAL APPLICATION CIRCUITS
Figure3. 12V VIN, 5V/2A
Figure4. 12V VIN, 3.3V/2A
Figure5. 12V VIN, 2.5V/2A
REV1.0
- SEP 2016 RELEASED -
- 10 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
Figure6. 12V VIN, 1.8V/2A
Figure7. 12V VIN, 1.2V/2A
REV1.0
- SEP 2016 RELEASED -
- 11 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
www.ait-ic.com
PACKAGE INFORMATION
Dimension in SOT-26 (Unit: mm)
REV1.0
- SEP 2016 RELEASED -
- 12 -
A7222
AiT Semiconductor Inc.
DC-DC CONVERTER BUCK (STEP-DOWN)
500kHz, 18V, 2A SYNCHRONOUS
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 server 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
- SEP 2016 RELEASED -
- 13 -
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