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AiT Semiconductor Inc.
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A7231
DESCRIPTION
FEATURES
ORDERING INFORMATION
Package Type
Part Number
APPLICATION
TYPICAL APPLICATION
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
The A7231 is a current mode monolithic buck
voltage converter. Operating with an input range of
4.5V-18V, the A7231 delivers 3A of continuous
output current with two integrated N-Channel
MOSFETs. At light loads, regulators operate in low
frequency to maintain high efficiency and low output
ripple.
The A7231 guarantees robustness with over current
protection, thermal protection, start-up current
run-away protection, and input under voltage lockout.
The A7231 is available in TSOT-26 package.
4.5V to 18V operating input range
3A output current
Up to 95% efficiency
High efficiency at light load
Fixed 420kHz Switching frequency
Input under voltage lockout
Start-up current run-away protection
Over current protection and Hiccup
Thermal protection
Available in TSOT-26 Package
Distributed Power Systems
Networking Systems
FPGA, DSP, ASIC Power Supplies
Green Electronics/ Appliances
TSOT-26 TE6
V: Halogen free Package
Note
R: Tape & Reel
AiT provides all RoHS products
Suffix “ V “ means Halogen free Package
A7231TE6R
A7231TE6VR
Notebook Computers
3A Buck Voltage Converter
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A7231
Pin #
Symbol
Function
PIN DESCRIPTION
1 GND Power ground pin.
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
Top View
2 SW
SW is the switching node that supplies power to the output. Connect the
output LC filter from SW to the output load.
supplies power to the IC. Connect a 4.5V to 18V supply
IN
3 IN
Input voltage pin. V
to V
and bypass VIN to GND with a suitably large capacitor to eliminate noise
IN
on the input to the IC.
Output feedback pin. FB senses the output voltage and is regulated by the
4 FB
control loop to 0.6V. Connect a resistive divider at FB.
5 EN Drive EN pin high to turn on the regulator and low to turn off the regulator.
Boostrap pin for top switch. A 0.1uF or larger capacitor should be connected
6 BST
between this pin and the SW pin to supply current to the top switch and top
switch driver.
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A7231
Parameter
Symbol
Min
Max
Units
Package
θJA
θJC
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
ABSOLUTE MAXIMUM RATINGS
VIN, EN, SW PIN -0.3V ~ 19V
BST PIN SW-0.3V to SW+5V
FB PIN -0.3V to 2.5V
Junction Temperature
Lead Temperature 260ºC
Storage Temperature -65ºC ~ +150ºC
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: The A7231 guarantees robust performance from -40°C to 150°C junction temperature. The junction temperature range
specification is assured by design, characterization and correlation with statistical process controls.
NOTE2: The A7231 includes thermal protection that is intended to protect the device in overload conditions. Thermal protection is active
when junction temperature exceeds the maximum operating junction temperature. Continuous operation over the specified
absolute maximum operating junction temperature may damage the device.
NOTE1,2
150ºC
RECOMMENDED OPERATING CONDITIONS
Input Voltage VIN 4.5 18 V
Output Voltage V
OUT
0.8 16.2 V
Junction Temperature TJ -40 125 ºC
THERMAL PERFORMANCE
TSOT-26
NOTE3: Measured on JESD51-7, 4-layer PCB.
NOTE3
110°C/W 55°C/W
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A7231
Parameter
Symbol
Conditions
Min.
Typ.
Max.
Unit
ELECTRICAL CHARACTERISTICS
VIN=12V, TA=25℃, unless otherwise stated.
V
Undervoltage Lockout Threshold V
IN
IN_MIN
V
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
falling 3.9 4.1 V
IN
VIN Undervoltage Lockout Hysteresis V
IN_MIN_HYST
V
rising 250 mV
IN
Shutdown Supply Current ISD VEN=0V 0.2 0.3 μA
Supply Current IQ VEN=5V, VFB=2V 80 100 μA
Feedback Voltage VFB 588 600 612 mV
Top Switch Resistance
Bottom Switch Resistance
Top Switch Leakage Current I
Bottom Switch Leakage Current I
Top Switch Current Limit
NOTE4
R
NOTE4
R
NOTE4
I
DS(ON)T
DS(ON)B
LEAK_TOP
LEAK_BOT
LIM_TOP
115 mΩ
71 mΩ
V
=16V, VEN=0V,
IN
V
=0V
SW
V
=16V, VEN=0V,
IN
V
=0V
SW
0.5 μA
0.5 μA
Minimum Duty Cycle 5.5 A
Switch Frequency FSW 420 kHz
Minimum On Time
Minimum Off Time
EN Shut Down Threshold Voltage V
EN Shut Down Hysteresis V
Thermal Shutdown
Temperature Hysteresis
NOTE4: Guaranteed by design.
NOTE4
T
NOTE4
T
NOTE4
T
NOTE4
T
100 ns
ON_MIN
VFB=0.7V 130 ns
OFF_MIN
VEN falling, FB=0V 1.2 V
EN_TH
VEN rising, FB=0V 100 mV
EN_HYST
145 ℃
TSD
20 ℃
HYS
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A7231
1. Steady State Test
VIN=12V, V
OUT
=3.3V, I
OUT
=3A
2. Startup through Enable
VIN=12V, V
OUT
=3.3V, I
OUT
=3A(Resistive load)
3. Shutdown through Enable
VIN=12V, V
OUT
=3.3V, I
OUT
=3A(Resistive load)
4. Heavy Load Operation
2A LOAD
5. Medium Load Operation
1A LOAD
6. Light Load Operation
0 A LOAD
TYPICAL PERFORMANCE CHARACTERISTICS
=12V, V
V
IN
= 3.3V, L = 4.7μH, C
OUT
= 47μF, TA = +25°C, unless otherwise noted
OUT
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
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A7231
7. Short Circuit Protection
VIN=12V, V
OUT
=3.3V, I
OUT
=3A- Short
8. Short Circuit Recovery
VIN=12V, V
OUT
=3.3V, I
OUT
= Short-3A
9. Load Transient
1.5A LOAD → 3A LOAD → 1.5A LOAD
10. Quiescent Current vs. Temp
VIN=12V, V
OUT
=3.3V, VEN=2.5V, VFB=0.8V
11. Quiescent Current vs. Input Voltage
12. Feedback Voltage vs. Temp.
@ different temperature
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
VIN=12V, V
=3.3V, VEN=2.5V, VFB=0.8V
OUT
VIN=5V, VEN=2.5V, Sweep FB voltage
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A7231
13. Quiescent Current @ Temperature =25℃
Efficiency @ V
OUT
=5V
14. Efficiency @ V
OUT
=3.3V
15. Load regulation @ V
OUT
=3.3V
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
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A7231
BLOCK DIAGRAM
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
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AiT Semiconductor Inc.
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A7231
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
DETAILED INFORMATION
The A7231 is a synchronous, buck voltage converter.
Current-Mode Control
The A7231 utilizes current-mode control to regulate the FB voltage. Voltage at the FB pin is regulated at 0.6V
so that by connecting an appropriate resistor divider between V
and GND, designed output voltage can be
OUT
achieved.
PFM Mode
The A7231 operates in PFM mode at light load. In PFM mode, switch frequency decreases when load current
drops to boost power efficiency at light load by reducing switch-loss, while switch frequency increases when
load current rises, minimizing output voltage ripples.
Internal Soft-start
Soft-Start makes output voltage rising smoothly follow an internal SS voltage until SS voltage is higher than
the internal reference voltage. It can provide overshoot of output voltage when startup.
Power Switch
N-Channel MOSFET switches are integrated on the A7231 to down convert the input voltage to the regulated
output voltage. Since the top MOSFET needs a gate voltage greater than the input voltage, a boost capacitor
connected between BST and SW pins is required to drive the gate of the top switch. The boost capacitor is
charged by the internal 3.3V rail when SW is low.
V
Under-Voltage Protection
IN
A resistive divider can be connected between VIN and ground, with the central tap connected to EN, so that
when V
drops to the pre-set value, EN drops below 1.2V to trigger input under voltage lockout protection.
IN
Output Current Run-Away Protection
At start-up, due to the high voltage at input and low voltage at output, current inertia of the output inductance
can be easily built up, resulting in a large start-up output current. A valley current limit is designed in the
A7231 so that only when output current drops below the valley current limit can the top power switch be
turned on. By such control mechanism, the output current at start-up is well controlled.
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A7231
12
2
RRR+
V
OUT
(V)
R1(kΩ)
R2(kΩ)
−
IN
OUT
IN
OUT
V
V
1x
V
V
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
Over Current Protection and Hiccup
A7231 has a cycle-by-cycle current limit. When the inductor current triggers current limit, A7231 enters hiccup
mode and periodically restart the chip. A7231 will exit hiccup mode while not triggering current limit.
Thermal Protection
When the temperature of the A7231 rises above 145°C, it is forced into thermal shut-down. Only when core
temperature drops below 125°C can the regulator becomes active again.
Application Information
Output Voltage Set
The output voltage is determined by the resistor divider connected at the FB pin, and the voltage ratio is:
where V
is the feedback voltage and V
FB
OUT
Choose R2 around 10kΩ~15kΩ, and then R
V
FB=VOUT
is the output voltage.
can be calculated by:
1
x
The following table lists the recommended values.
2.5 47 15
3.3 49.5 11
5 110 15
Input Capacitor
The input capacitor is used to supply the AC input current to the step-down converter and maintaining the DC
input voltage. The ripple current through the input capacitor can be calculated by:
= I
LOAD
x
I
C1
where I
is the load current, V
LOAD
Thus the input capacitor can be calculated by the following equation when the input ripple voltage is
determined.
typically allowed to be 30% of the maximum
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is the output voltage, VIN is the input voltage.
OUT
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A7231
L S
OUT
xΔIf
V
−
IN
OUT
V
V
1
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
where C1 is the input capacitance value, fS is the switching frequency, ΔVIN is the input ripple voltage.
The input capacitor can be electrolytic, tantalum or ceramic. To minimizing the potential noise, a small X5R or
X7R ceramic capacitor, i.e. 0.1uF, should be placed as close to the IC as possible when using electrolytic
capacitors.
A 22uF ceramic capacitor is recommended in typical application.
Output Capacitor
The output capacitor is required to maintain the DC output voltage, and the capacitance value determines the
output ripple voltage. The output voltage ripple can be calculated by:
where C
is the output capacitance value and R
2
is the equivalent series resistance value of the output
ESR
capacitor.
The output capacitor can be low ESR electrolytic, tantalum or ceramic, which lower ESR capacitors get lower
output ripple voltage.
The output capacitors also affect the system stability and transient response, and a 47uF ceramic capacitor is
recommended in typical application.
Inductor
The inductor is used to supply constant current to the output load, and the value determines the ripple current
which affect the efficiency and the output voltage ripple. The ripple current is switch current limit, thus the
inductance value can be calculated by:
where V
is the input voltage, V
IN
L =
is the output voltage, fs is the switching frequency, and ΔIL is the
OUT
x
peak-to-peak inductor ripple current.
External Boostrap Capacitor
A boostrap capacitor is required to supply voltage to the top switch driver. A 0.1uF low ESR ceramic capacitor
is recommended to connected to the BST pin and SW pin.
Load Transient Improvement
To improve the load transient performance, a feed forward capacitor (Cff) can be added in parallel with the
feedback resistor (R
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). (Figure1.). At the same time, to avoid the voltage offset which is caused by substrate
1
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A7231
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
injection, a 20k resistor (R0) is recommended to insert between the FB PIN and resistance divider.
Figure 1
PCB Layout Note
For minimum noise problem and best operating performance, the PCB is preferred to following the guidelines
as reference.
1. Place the input decoupling capacitor as close to A7231 (V
pin and PGND) as possible to eliminate noise
IN
at the input pin. The loop area formed by input capacitor and GND must be minimized.
2. Put the feedback trace as far away from the inductor and noisy power traces as possible.
3. The ground plane on the PCB should be as large as possible for better heat dissipation.
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A7231
Reference 1:
Reference 2:
REFERENCE DESIGN
VIN : 4.5V ~ 18 V
V
: 3.3V
OUT
I
: 0~3A
OUT
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
V
: 6.5V ~ 18 V
IN
V
: 5V
OUT
I
: 0~3A
OUT
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A7231
PACKAGE INFORMATION
Dimension in TSOT-26 (Unit: mm)
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
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AiT Semiconductor Inc.
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A7231
DC-DC CONVERTER BUCK (STEP-DOWN)
3A, 18V SYNCHRONOUS
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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