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AiT Semiconductor Inc.
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
DESCRIPTION
FEATURES
The A7312 is a high efficiency current-mode
asynchronous, 24V/1.2A buck converter. Its input
voltage ranges from 4V to 24V and it provides an
adjustable regulated output voltage from 0.81V to
5.5V while delivering up to 1.2A of output current.
The switching frequency is set to 1.4MHz, which
works with a inductor as small as 4.7uH. And the
A7312 will automatically switch between PFM and
PWM mode based on the load current, thus to
enhance the converter efficiency at light load.
A7312 consists of many protection blocks such as
UVLO, input voltage over voltage protection to stand
much higher input voltage spike, thermal protection
and output short circuit protection.
The A7312 is available in SOT-26 package.
ORDERING INFORMATION
Package Type
Part Number
SOT-26
E6
A7312E6R
A7312E6VR
Note
V: Halogen free Package
R: Tape & Reel
AiT provides all RoHS products
Suffix “ V “ means Halogen free Package
Adjustable Output Voltage, V
FB
=0.81V
Output current is up to 1.2A
Range of operation input voltage: 4~24V
Input voltage UVLO: 3.7V (voltage decreasing)
Input Overvoltage Protection @26V
Withstand input voltage spike >30V
Operating current at zero load: 0.8mA (typ.)
Line regulation: 0.1%/V (typ.)
Load regulation: 10mV (typ.)
High efficiency, up to 90%
Environment Temperature: -20°C ~85°C
Available in SOT-26 Package
APPLICATION
Security Camera
Consumer Electronic Device for automobile
Portable DVD
ADSL Modem, WLAN router
Other 12V or double cell Li-ion battery powered
device
TYPICAL APPLICATION
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AiT Semiconductor Inc.
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
PIN DESCRIPTION
Top View
Pin #
Symbol
Function
1
BST
High side power transistor gate drive boost input
2
GND
Ground. 3 FB
Feedback input with reference voltage set to 0.81V
4
EN
Enable input. Setting it to high level or connecting to Vin via a resistor
may turn on the chip, while setting it to ground level will turn off the chip.
5
VIN
Power input, the input capacitor should be placed as close to VIN and
GND pin as possible
6
SW
Power switching node to connect inductor
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AiT Semiconductor Inc.
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
ABSOLUTE MAXIMUM RATINGS
Max Input Voltage
30V
TJ, Max Operating Junction Temperature
125°C
TA, Ambient Temperature
-20°C ~ 85°C
Package Thermal Resistance
SOT-26 (θJC)
110°C / W
SOT-26 (θJA)
220°C / W
TS, Storage Temperature
-40°C ~150°C
Lead Temperature & Time
260°C, 10S
HBM, ESD
>2KV
Parameter
Symbol
MIN
MAX
Units
Input Voltage Range
4
24
V
Output Voltage Range
0.81
5.5
V
Operating Junction Temperature
TJ
-20
125
°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.
RECOMMENDED OPERATING CONDITIONS
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AiT Semiconductor Inc.
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
ELECTRICAL CHARACTERISTICS
Parameter
Symbol
Conditions
Min.
Typ.
Max.
Unit
Input Voltage Range
VDD
4
24
V
Output Voltage Range
V
OUT
0.81 5.5
V
Feedback Voltage
Vref
VIN=12V, VEN=5V
0.79
0.81
0.83
V
UVLO Voltage
V
UVLO
VIN H-->L, I
OUT
=0.5A
3.7 V
Feedback Leakage Current
Ifb
0.1
0.4
uA
Quiescent Current
IQ
Active, VFB=1V, No Switching
0.6
1.0
mA
Shutdown, VIN=8V
6 10
uA
Line Regulation
LnReg
VIN=5V to 12V
0.1 %/V
Load Regulation
LdReg
I
OUT
=0.1 to 1.2A
0.02
%/A
Switching Frequency
F
SOC
VEN=3V, VIN=12V
1.0
1.4
1.8
MHz
High side Switch R
DSON
R
DSON_H
ISW=200mA
250
350
mohm
Peak Inductor Current Limit
I
LIMIT
VIN=12V, V
OUT
=5V
1.5 2 A EN High Threshold
V
EN_H
1 1.5 3 V
EN Low Threshold
V
EN_L
0.5
V
Input Over-Voltage Protection
V
OVP
VEN=3V
26 V
Over Temperature Protection
TSD
Hystersis=40°C
150 °C
VIN=12V, TA=25°C
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
1. Efficiency vs I
OUT
, V
OUT
=5.0V
2. Line Regulation, V
OUT
=5.0V
3. Load Regulation, V
OUT
=5.0V
4. Input Current at Zero Load, I
OUT
=0mA
5. Switching Waveform, V
IN
=12V, I
OUT
=0.5A
CH1=VIN, CH2=V
OUT
, CH3=SW, CH4=ISW
6. Switching Waveform, V
IN
=12V, I
OUT
=1A
CH1=VIN, CH2=V
OUT
, CH3=SW, CH4=ISW
VIN=12V, V
=5.0V, L=4.7uH, CIN=10uF, C
OUT
=22uF, TA=25°C, unless otherwise stated
OUT
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
7. Switching Waveform, V
IN
=24V, I
OUT
=0.5A
CH1=VIN, CH2=V
OUT
, CH3=SW, CH4=ISW
8. Switching Waveform, V
IN
=24V, I
OUT
=1A
CH1=VIN, CH2=V
OUT
, CH3=SW, CH4=ISW
9. Load Transient Response, V
IN
=12V, I
OUT
=0.12~1A
CH1=VIN, CH2=V
OUT,
CH4=ISW
10. Load Transient Response, V
IN
=24V, I
OUT
=0.12~1A
CH1=VIN, CH2=V
OUT,
CH4=ISW
11. Input Current at Zero Load
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AiT Semiconductor Inc.
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
BLOCK DIAGRAM
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AiT Semiconductor Inc.
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
DETAILED INFORMATION
V
OUT
(V)
C
OUT
(μF)
L(μH)
5.0
22
6.8~10
3.3
22
4.7~10
2.5
22
3.3~10
Functional Description
Loop Operation
The A7312 is a wide input range, high-efficiency, DC-to-DC step-down switching regulator, capable of
delivering up to 1.2A of output current, integrated with a 250mΩ MOSFET, with external schottky diode. It
uses a PWM current-mode control scheme. An error amplifier integrates error between the FB signal and the
internal reference voltage. The output of the integrator is then compared to the sum of a current-sense signal
and the slope compensation ramp. This operation generates a PWM signal that modulates the duty cycle of
the power MOSFETs to achieve regulation for output voltage.
Current Limit
There is a cycle-by-cycle current limit on the high-side MOSFET of 1.5A (typ). When the current flowing out of
SW exceeds this limit, the high-side MOSFET turns off and the external schottky diode rectifier turns on.
Unlike the traditional method of current limiting by limiting the voltage at the internal compensation node,
which usually has large variation due to duty cycle variance, this type of peak current limiting scheme
provides a relatively more accurate limit for output current, thereby lowering the requirements for system
design.
Light Load Operation
Traditionally, a fixed current mode constant frequency PWM DC-DC regulator always switches even when the
output load is small. When energy is shuffling back and forth through the power MOSFETs, power is lost due
to the finite RDSONs of the MOSFETs and parasitic capacitances. At light load, this loss is prominent and
efficiency is therefore very low. A7312 employs a proprietary control scheme that improves efficiency in this
situation by enabling the device into a power save mode during light load, thereby extending the range of high
efficiency operation.
Component Selection
When setting up the A7312 for different output voltage, please use following recommended component value
for the best performance.
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AiT Semiconductor Inc.
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
Thermal Consideration
A7312 is high efficiency Buck converter, which means it consumes very few power when converting the high
voltage to low voltage. However, when output power is very large, like 5V/1.2A, the output power is as high as
6W, a heat dissipation path is strongly recommended to be routed on PCB. A7312 is in SOT-26 package. The
heat is conducted out via Pin 2 (GND), so the heat dissipation route on PCB should be connected to the Pin 2
of the chip.
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AiT Semiconductor Inc.
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
PACKAGE INFORMATION
SYMBOL
MIN
MAX
A
1.100
1.400
A1
0.000
0.100
A2
1.000
1.300
b
0.200
0.500
c
0.100
0.250
D
2.700
3.100
E
1.500
1.800
E1
2.500
3.100 e 0.950(BSC)
e1
1.700
2.100
L
0.200 - θ
0°
8°
Dimension in SOT-26 Package (Unit: mm)
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A7312
DC-DC CONVERTER/ BUCK (STEP-DOWN)
24V/1.2A ASYNCHRONOUS BUCK CONVERTER
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.
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