A7230 [AITSEMI]
SYNCHRONOUS, WIDE INPUT RANGE STEP-DOWN CONVERTER;
| 型号： | A7230 |
| 厂家： | 
AiT Semiconductor |
| 描述： | SYNCHRONOUS, WIDE INPUT RANGE STEP-DOWN CONVERTER 输入元件 |
| 文件： | 总16页 (文件大小：465K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
DESCRIP≤ION
FEA≤≥RES
≤he A7230 is a monolithic synchronous buck
regulator. ≤he device integrates 100mΩ MOSFE≤S
that provide 3A continuous load current over a wide
operating input voltage of 4.75V to 18V. Current mode
control provides fast transient response and
cycle-by-cycle current limit.
3A Output Current
Wide 4.75V to 18V Operating Input Range
Integrated 100mΩ Power MOSFE≤ Switches
Output Adjustable from 0.925V to 15V
≥p to 95% Efficiency
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Fixed 370KHz Frequency
An adjustable soft-start prevents inrush current at
turn-on. In shutdown mode, the supply current drops
below 1μA.
Cycle-by-Cycle Over Current Protection
Input ≥nder Voltage Lockout
Available in PSOP8 package
≤he A7230 provides a very compact system solution
with minimal reliance on external components.
APPLICA≤ION
≤he A7230 is available in PSOP8 Package.
Distributed Power Systems
Networking Systems
FPGA, DSP, ASIC Power Supplies
Green Electronics/ Appliances
Notebook Computers
ORDERING INFORMA≤ION
Package ≤ype
PSOP8
Part Number
A7230MP8R
A7230MP8VR
MP8
≤YPICAL APPLICA≤ION
R: ≤ape & Reel
Note
V: Halogen free Package
Ai≤ provides all RoHS products
Suffix ꢀ V ꢀ means Halogen free Package
REV1.0
- MAR 2011 RELEASED -
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
PIN DESCRIP≤ION
≤op View
Name
BS
Description
Pin #
1
High-Side Gate Drive Boost Input. BS supplies the drive for the
high-side N-Channel MOSFE≤ switch. Connect a 0.01μF or greater
capacitor from SW to BS to power the high side switch.
Power Input. IN supplies the power to the IC, as well as the step-down
converter switches. Drive IN with a 4.75V to 18V power source. Bypass
IN to GND with a suitably large capacitor to eliminate noise on the input
to the IC. See Input Capacitor.
Power Switching Output. SW is the switching node that supplies power
to the output. Connect the output LC filter from SW to the output load.
Note that a capacitor is required from SW to BS to power the high-side
switch.
2
3
IN
SW
4
5
GND
FB
Ground (Connect Exposed Pad to Pin 4).
Feedback Input. FB senses the output voltage to regulate that voltage.
Drive FB with a resistive voltage divider from the output voltage. ≤he
feedback threshold is 0.925V. See Setting the Output Voltage.
Compensation Node. COMP is used to compensate the regulation
control loop. Connect a series RC network from COMP to GND to
compensate the regulation control loop. In some cases, an additional
capacitor from COMP to GND is required. See Compensation
Components.
6
COMP
Enable Input. EN is a digital input that turns the regulator on or off.
Drive EN high to turn on the regulator, drive it low to turn it off. Pull up
with 100kΩ resistor for automatic startup.
Soft-Start Control Input. SS controls the soft-start period. Connect a
capacitor from SS to GND to set the soft-start period. A 0.1μF capacitor
sets the soft-start period to 15ms. ≤o disable the soft-start feature,
leave SS unconnected.
7
8
EN
SS
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
ABSOL≥≤E MAXIM≥M RA≤INGS
VIN, Supply Voltage
-0.3V to 20V
-1V to VIN + 0.3V
VSW-0.3V to VSW + 6V
-0.3V to +6V
VSW, Switch Voltage
VBS, Bootstrap Voltage
VEN, Enable/≥VLO Voltage
VCOMP, Comp Voltage
VFB, Feedback Voltage
Junction ≤emperature
Lead ≤emperature
-0.3V to +6V
-0.3V to +6V
+150℃
+260℃
Storage ≤emperature
-55°C to +150℃
Stresses above may cause permanent damage to the device. ≤hese are stress ratings only and functional operation of the device at
these or any other conditions beyond those indicated in the Electrical Characteristics are not implied. Exposure to absolute maximum
rating conditions for extended periods may affect device reliability.
RECOMMENDED OPERA≤ING CONDI≤IONS
VIN, Input Voltage
4.75V to 18V
0.925 to 15V
-20℃to +85℃
VSW, Output Voltage
Operating ≤emperature
≤HERMAL RESIS≤ANCE
Package
θJA
θJC
10℃/W
P-SOP8
50℃/W
NO≤E: Measured on approximately 1ꢁ square of 1 oz copper
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
ELEC≤RICAL CHARAC≤ERIS≤ICS
VIN = 12V, ≤A = +25℃, unless otherwise noted.
Parameter
Conditions
Min
≤yp
0.3
1.3
925
1.1
480
800
100
100
0
Max
≥nit
μA
mA
mV
V
Shutdown Supply Current
Supply Current
VEN ꢂ 0.3V
-
3
VEN ꢃ 2.6V, VFB = 1.0V
4.75Vꢂ VIN ꢂ18V
-
1.5
Feedback Voltage
900
950
Feedback Overvoltage ≤hreshold
Error Amplifier Voltage
-
-
-
-
V/V
μA/V
mΩ
mΩ
μA
A
Error Amplifier ≤ransconductance
High-Side Switch-On Resistance
Low-Side Switch-On Resistance
High-Side Switch Leakage
≥pper Switch Current Limit
Lower Switch Current Limit
COMP to Current Sense ≤ransconductance
Oscillator Frequency
ΔIC = ±10μA
-
-
-
-
-
-
VEN = 0V, VSW = 0V
-
10
4
6
-
-
0.9
5.2
370
150
90
-
A
-
-
А/V
KHz
KHz
%
310
390
Short Circuit Frequency
VFB = 0V
-
-
Maximum Duty Cycle
VFB = 1.0V
-
-
Minimum On ≤ime
-
220
1.3
200
2.5
210
4.05
210
6
-
nS
V
EN Shutdown ≤hreshold Voltage
EN Shutdown ≤hreshold Voltage Hysterisis
EN Lockout ≤hreshold Voltage
EN Lockout Hysterisis
VEN Rising
1.1
1.5
-
-
mV
V
2.2
2.7
-
-
mV
V
Input ≥VLO ≤hreshold Rising
Input ≥VLO ≤hreshold Hysteresis
Soft-start Current
VIN Rising
3.8
4.4
-
-
-
-
-
-
-
-
mV
μA
ms
°C
VSS = 0V
Soft-start Period
CSS = 0.1μF
15
≤hermal Shutdown
160
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
APPLICA≤ION CIRC≥I≤
Figure 1. ≤ypical Application Circuit
Figure 2. ≤ypical Efficiency Curve, VO≥≤=5V
A7230 with 3.3V output, 2x22uF Ceramic Output
capacitor
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
≤YPICAL PERFORMENCE CHARAC≤ERIS≤ICS
1. Short circuit test (Channel3:ISW, Channel2:VO)
2. Soft-start (Channel1:EN, Channel2:VO)
3. ≤ransient response
4. Ripple
(Channel3:ISW,Channel2:VO)
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
BLOCK DIAGRAM
REV1.0
- MAR 2011 RELEASED -
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
DE≤AILED INMFORMA≤ION
≤he A7230 is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from
4.75V to 18V down to an output voltage as low as 0.925V, and supplies up to 3A of load current.
≤he A7230 uses current-mode control to regulate the output voltage. ≤he output voltage is measured at FB
through a resistive voltage divider and amplified through the internal transconductance error amplifier. ≤he
voltage at the COMP pin is compared to the switch current measured internally to control the output voltage.
≤he converter uses internal N-Channel MOSFE≤ switches to step-down the input voltage to the regulated
output voltage. Since the high side MOSFE≤ requires a gate voltage greater than the input voltage, a boost
capacitor connected between SW and BS is needed to drive the high side gate. ≤he boost capacitor is
charged from the internal 5V rail when SW is low.
When the A7230 FB pin exceeds 20% of the nominal regulation voltage of 0.925V, the over voltage
comparator is tripped and the COMP pin and the SS pin are discharged to GND, forcing the high-side switch
off.
Component Selection Setting the Output Voltage
≤he output voltage is set using a resistive voltage divider from the output voltage to FB (see ≤ypical
Application circuit on page 1). ≤he voltage divider divides the output voltage down by the ratio:
Where VFB is the feedback voltage and VO≥≤ is the output voltage.
≤hus the output voltage is:
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
R2 can be as high as 100kΩ, but a typical value is 10kΩ. ≥sing the typical value for R2, R1 is determined by:
For example, for a 3.3V output voltage, R2 is 10kΩ, and R1 is 26.1kΩ. ≤able 1 lists recommended resistance
values of R1 and R2 for standard output voltages.
≤able.1 Recommended Resistance Values
VO≥≤
1.8V
2.5V
3.3V
5V
R1
R2
9.53kΩ
16.9kΩ
26.1kΩ
44.2kΩ
121kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
12V
Inductor
≤he 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. ≤he inductance value can be calculated by:
Where VO≥≤ 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. ≤he peak inductor current
can be calculated by:
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
Where ILOAD is the load current.
≤he choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI
requirements.
Optional Schottky Diode
During the transition between high-side switch and low-side switch, the body diode of the low-side power
MOSFE≤ conducts the inductor current. ≤he forward voltage of this body diode is high. An optional Schottky
diode may be paralleled between the SW pin and GND pin to improve overall efficiency.
Input Capacitor
≤he 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. ≥se 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. ≤he RMS current in the input capacitor
can be estimated by:
≤he worst-case condition occurs at VIN = 2VO≥≤, where ICIN = ILOAD/2. For simplification, choose the input
capacitor whose RMS current rating greater than half of the maximum load current. ≤he input capacitor can
be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, a small, high quality
ceramic capacitor, i.e. 0.1μF, 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. ≤he input voltage ripple for low ESR capacitors can be estimated by:
Where C1 is the input capacitance value.
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
Output Capacitor
≤he 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. ≤he
output voltage ripple can be estimated by:
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. ≤he output voltage ripple is mainly caused by the capacitance. For simplification, the output
voltage ripple can be estimated by:
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:
≤he characteristics of the output capacitor also affect the stability of the regulation system. ≤he A7230 can be
optimized for a wide range of capacitance and ESR values.
Compensation Components
A7230 employs current mode control for easy compensation and fast transient response. ≤he sys- tem
stability and transient response are controlled through the COMP pin. COMP pin is the output of the internal
transconductance error amplifier. A series capacitor-resistor combination sets a pole-zero combination to
control the characteristics of the control system. ≤he DC gain of the voltage feedback loop is given by:
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
Where VFB is the feedback voltage, 0.925V; AVEA is the error amplifier voltage gain; GCS is the current sense
transconductance and RLOAD is the load resistor value. ≤he system has two poles of importance. One is due
to the compensation capacitor (C3) and the output resistor of the error amplifier, and the other is due to the
output capacitor and the load resistor. ≤hese poles are located at:
Where GEA is the error amplifier transconductance.
≤he system has one zero of importance, due to the compensation capacitor (C3) and the compensation
resistor (R3). ≤his zero is located at:
≤he system may have another zero of importance, if the output capacitor has a large capacitance and/or a
high ESR value. ≤he zero, due to the ESR and capacitance of the output capacitor, is located at:
In this case (as shown in Figure 4), a third pole set by the compensation capacitor (C6) and the compensation
resistor (R3) is used to compensate the effect of the ESR zero on the loop gain. ≤his pole is located at:
≤he goal of compensation design is to shape the converter transfer function to get a desired loop gain. ≤he
system crossover frequency where the feedback loop has the unity gain is important. Lower crossover
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
frequencies result in slower line and load transient responses, while higher crossover frequencies could
cause system instability. A good rule of thumb is to set the cross- over frequency below one-tenth of the
switching frequency.
≤o optimize the compensation components, the following procedure can be used.
1. Choose the compensation resistor (R3) to set the desired crossover frequency. Determine the R3 value by
the following equation:
Where fc is the desired crossover frequency which is typically below one tenth of the switching frequency.
2. Choose the compensation capacitor (C3) to achieve the desired phase margin. For applications with typical
inductor values, setting the compensation zero, fZ1, below one-forth of the crossover frequency provides
sufficient phase margin. Determine the C3 value by the following equation:
Where R3 is the compensation resistor.
3. Determine if the second compensation capacitor (C6) is required. It is required if the ESR zero of the output
capacitor is located at less than half of the switching frequency, or the following relationship is valid:
If this is the case, then add the second compensation capacitor (C6) to set the pole fP3 at the location of the
ESR zero. Determine the C6 value by the equation:
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
External Bootstrap Diode
An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external
BS diode are:
● VO≥≤ is 5V or 3.3V
● Duty cycle is high: D=VO≥≤/VIN > 65%
In these cases, an external BS diode is recommended from the output of the voltage regulator to BS pin, see
below:
Add Optional External Bootstrap Diode to Enhance Efficiency
≤he recommended external BS diode is IN4148, and the BS cap is 0.1~1μF.
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- MAR 2011 RELEASED -
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
PACKAGE INFORMA≤ION
Dimension in PSOP8 Package (≥nit: mm)
Symbol
Min
Max
A
A1
A2
b
1.350
0.050
1.350
0.330
0.170
4.700
3.202
3.800
5.800
2.313
1.750
0.150
1.550
0.510
0.250
5.100
3.402
4.000
6.200
2.513
c
D
D1
E
E1
E2
e
1.270(BSC)
L
0.400
0°
1.270
8°
θ
REV1.0
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A7230
AiT Semiconductor Inc.
www.ait-ic.com
3A, 18V SYNCHRONOUS, WIDE INPUT RANGE
STEP-DOWN CONVERTER
IMPOR≤AN≤ NO≤ICE
Ai≤ Semiconductor Inc. (Ai≤) 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.
Ai≤ 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. ≥se of Ai≤
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.
Ai≤ Semiconductor Inc. assumes to no liability to customer product design or application support. Ai≤
warrants the performance of its products of the specifications applicable at the time of sale.
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