A7221AE6R [AITSEMI]
DC-DC CONVERTER BUCK (STEP-DOWN) SYNCHRONOUS;
| 型号： | A7221AE6R |
| 厂家： | 
AiT Semiconductor |
| 描述： | DC-DC CONVERTER BUCK (STEP-DOWN) SYNCHRONOUS DC-DC转换器 |
| 文件： | 总13页 (文件大小：423K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
DESCRIPTION
FEATURES
A7221A is simple, easy to use, 2A synchronous
step-down (Buck) convertor in SOT-26 package, with
high efficiency and fast transient response. A7221A
operates over a wide input voltage range from 4.5V to
16V and integrates main switch and synchronous
switch with very low RDS(ON) to minimize the
conduction loss. A7221A adopts the active constant
on time PWM architecture to achieve fast transient
responses for high step down applications and high
efficiency at light loads. In addition, it keeps in
constant frequency of 500kHz under heavy load
conditions to minimize the size of inductor and
capacitor. Fault conditions also include cycle-by-cycle
current limit, output under voltage protection, output
over current protection, output short-circuit protection
and thermal shutdown
Integrated 130mΩ and 120mΩ FETs
4.5~16V input voltage range
2A load current capability
Active constant on time PWM architecture with
500kHz switching frequency
Internal soft-start limits the inrush current
2% 0.6V reference
Available in SOT-26 Package
APPLICATION
Set Top Box
Portable TV
Access Point Router
DSL Modem
LCD TV
TYPICAL APPLICATION
The A7221A is available in SOT-26 package.
ORDERING INFORMATION
Package Type
SOT-26
Part Number
A7221AE6R
A7221AE6VR
E6
V: Halogen free Package
R: Tape & Reel
Note
SPQ:3,000pcs/Reel
AiT provides all RoHS products
Figure 1. Typical Application Circuit
Suffix “ V “ means Halogen free Package
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 1 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
PIN DESCRIPTION
Top View
Pin #
Symbol
Function
Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX
pin with 0.1uF ceramic cap.
1
2
BS
GND
Ground pin.
Output Feedback Pin. Connect this pin to the center point of the output
resistor divider (as shown in Figure 1) to program the output voltage:
3
FB
VOUT=0.6x(1+R1/R2).
4
5
6
EN
IN
Enable control. Pull high to turn on. Do not float.
Input pin. Decouple this pin to GND pin with at least 1uF ceramic cap.
Inductor pin. Connect this pin to the switching node of inductor.
LX
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 2 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
ABSOLUTE MAXIMUM RATINGS
VIN, Supply Voltage
VSW, Switch Voltage
VEN, Enable
-0.3V ~ 18V
-1V ~ VIN + 0.3V
-1V ~ VIN + 0.3V
-0.3V ~ +4V
VBS, Bootstrap Voltage
VFB, Feedback Voltage
Thermal Resistance NOTE1
θJA
-0.3V~ +4V
100℃/W
55℃/W
θJC
Junction Temperature
Lead Temperature (Soldering, 10s)
Storage Temperature
+150℃
+260℃
-65℃~+150℃
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.
NOTE1: Measured on approximately 1” square of 1oz copper.
RECOMMENDED OPERATING CONDITIONSNOTE2
Parameter
Symbol
VIN
Min.
4.5
Max.
16
Unit
V
Input Voltage
Operating Temperature
-40
85
℃
NOTE2: The device is not guaranteed to function outside of its operating conditions.
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 3 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
ELECTRICAL CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, L = 4.7uH, TA = 25°C, unless otherwise specified
Parameter
Shutdown Supply Current
Supply Current
Conditions
Min.
Typ.
10
Max.
20
Unit
μA
μA
mV
nA
mΩ
mΩ
μA
A
VEN=0V
IOUT=0, VFB=VREF×105%
5V<VIN<16V
350
600
Feedback Voltage
588
-50
612
50
FB Input Current
High-Side Switch-On Resistance
Low-Side Switch-On Resistance
High-Side Switch Leakage
Upper Switch Current Limit
Lower Switch Current Limit
Oscillator Frequency
130
120
0
VEN = 0V, VSW = 0V
10
3.0
3.5
1.3
500
A
kHz
V
EN Rising Threshold
1.2
3.8
EN Falling Threshold
Input UVLO Threshold Rising
Input UVLO Threshold Hysteresis
Min ON Time
0.4
4.5
V
VIN Rising
4.2
15
V
mV
ns
50
Soft-start Time
tSS
0.2
85
ms
%
Max Duty Cycle
Thermal Shutdown
160
℃
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 4 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
TYPICAL PERFORMANCE CHARACTERISTICS
1.
3.
5.
Efficiency vs. IOUT @VOUT=1.2V
Soft-Start (VIN=12V, VO=3.3V, IO=2A)
Short Circuit
2.
4.
6.
Efficiency vs. IOUT @VOUT=5V
Soft-Start (VIN=12V,VO=3.3V,IO=0A)
Short Circuit Recovery
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 5 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
7.
Efficiency vs. IOUT @VOUT=3.3V
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 6 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
BLOCK DIAGRAM
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 7 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
DETAILED INFORMATION
Operation
Functional Description
The A7221A is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from
4.5V to 16V down to an output voltage as low as 0.6V, and supplies up to 2A of load current.
The A7221A uses current-mode control to regulate the output voltage. The output voltage is measured at FB
through a resistive voltage divider and amplified through the internal transconductance error amplifier. The
converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output
voltage.
Application Information
Setting the Output Voltage
The output voltage is set using a resistive voltage divider from the output voltage to FB (see Typical
Application circuit on page 1). The voltage divider divides the output voltage down by the ratio:
R2
R1+R2
VFB = VOUT x
Where VFB is the feedback voltage and VOUT is the output voltage.
Thus the output voltage is:
R1
R2
VOUT = 0.6 x (1+
)
Inductor
The inductor is required to supply constant current to the output load while being driven by the switched input
voltage. A larger value inductor will result in less ripple current that will result in lower output ripple voltage.
However, the larger value inductor will have a larger physical size, higher series resistance, and/or lower
saturation current. A good rule for determining the inductance to use is to allow the peak-to-peak ripple
current in the inductor to be approximately 30% of the maximum switch current limit. Also, make sure that the
peak inductor current is below the maximum switch current limit. The inductance value can be calculated by:
V
OUT
V
V
OUT
L =
x (1-
)
F
S
x ΔI
L
IN
Where VOUT is the output voltage, VIN is the input voltage, fS is the switching frequency, and ΔIL is the
peak-to-peak inductor ripple current.
Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current
can be calculated by:
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 8 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
V
2 x F
OUT
V
V
OUT
ILP = ILOAD
+
x (1-
)
S
x L
IN
here ILOAD is the load current.
The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI
requirements.
Vendor
P/N
L(μH)
10
DCR(mΩ)
Isat(A)
3.2
AiT-Components
AiT-Components
PIA6045-100MA
PIA5040-4R7N
48
30
4.7
3.5
Table 1. Recommended Inductors
Input Capacitor
The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the
AC current to the step-down converter while maintaining the DC input voltage. Use low ESR capacitors for the
best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also
suffice. Choose X5R or X7R dielectrics when using ceramic capacitors. Since the input capacitor absorbs the
input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor
can be estimated by:
V
V
V
V
OUT
IN
I
C1 = ILOAD (1− OUT )x
IN
The worst-case condition occurs at VIN = 2VOUT, where ICIN = ILOAD/2. For simplification, choose the input
capacitor whose RMS current rating greater than half of the maximum load current. The input capacitor can
be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, a small, high quality 0.1uF
ceramic capacitor should be placed as close to the IC as possible. When using ceramic capacitors, make sure
that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input.
The input voltage ripple for low ESR capacitors can be estimated by:
ILOAD
C1x FS
V
V
OUT
IN
V
V
OUT
ΔVIN =
x
x (1-
)
IN
Where C1 s the value of the input capacitor.
Output Capacitor
The output capacitor is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic
capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The
output voltage ripple can be estimated by:
VOUT
FS x L
V
V
OUT
1
ΔVOUT
=
x (1-
) x (RESR
+
)
IN
6.28 x FS x C2
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 9 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
Where C2 is the output capacitance value and RESR is the equivalent series resistance (ESR) value of the
output capacitor. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by
the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output
voltage ripple can be estimated by:
V
OUT
V
V
OUT
ΔVOUT
=
x (1-
)
6.28 x FS2 x L x C2
IN
In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching
frequency. For simplification, the output ripple can be approximated to:
V
OUT
V
V
OUT
ΔVOUT
=
x (1-
) x RESR
FS
x L
IN
The characteristics of the output capacitor also affect the stability of the regulation system. The A7221A can
be optimized for a wide range of capacitance and ESR values. For A7221A normal operation, the input and
output can be an electrolytic capacitor in parallel.
VOUT
5.0V
3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
R1(kΩ)
91
R2(kΩ)
12
L1(uH)
4.7
C1(uF)
22
C2(uF)
22
53.6
39
12
4.7
22
22
12
4.7
22
22
24
12
4.7
22
22
18
12
4.7
22
22
12
12
4.7
22
22
8.2
12
4.7
22
22
Table 2 Recommended Component Values for typical Output Voltage
Layout Guidance
When laying out the PCB board, the following suggestions should be taken to ensure proper operation of the
A7221A.
1.
2.
3.
The power traces, including the GND trace, the SW trace and the VIN trace should be kept short, direct
and wide.
The FB pin should be connected directly to the feedback resistor. The resistive divider R1/R2 must be
connected between the (+) plate of C2 and ground.
Connect the (+) plate of C1 to the IN pin of A7221A as closely as possible. This capacitor provides the
AC current to internal power MOSFET.
4.
5.
Keep the switching node, SW, away from the sensitive VFB node.
Keep the (-) plates of C1 and C2 as close as possible.
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 10 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 11 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V SYNCHRONOUS
AiT Semiconductor Inc.
www.ait-ic.com
PACKAGE INFORMATION
Dimension in SOT-26 Package (Unit: mm)
Millimeters
Inches
Symbol
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
0.500
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
0.020
0.008
0.119
0.067
0.116
c
D
E
E1
e
0.950(BSC)
1.800
0.037(BSC)
e1
L
2.000
0.600
8°
0.071
0.012
0°
0.079
0.024
8°
0.300
0°
θ
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 12 -
A7221A
DC-DC CONVERTER BUCK (STEP-DOWN)
2A, 16V 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.
REV3.0
- DEC 2015 RELEASED, AUG 2016 UPDATED -
- 13 -
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