SE1484 [SEAWARD]
3A 27V Synchronous Buck Converter;
| 型号： | SE1484 |
| 厂家： | 
Seaward Electronics Inc. |
| 描述： | 3A 27V Synchronous Buck Converter |
| 文件： | 总8页 (文件大小：670K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SE1484
3A 27V Synchronous Buck Converter
General Description
Features
The SE1484 is a monolithic synchronous buck
regulator. The device integrates 95 mΩ MOSFETS
that provide 3A continuous load current over
3A Output Current
Wide 4.5V to 27V Operating Input Range
Output Adjustable from 0.925V to 0.8Vin
Up to 93% Efficiency
a
wide operating input voltage of
4.5V
to
27V.Current mode control provides fast transient
response and cycle-by-cycle current limit. An
adjustable soft-start prevents inrush current at turn on.
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Fixed 340KHZ Frequency
Cycle-by-Cycle Over Current Protection
Short Circuit Protection
Input Under Voltage Lockout
Package： PSOP-8
Pin Configuration
Applications
Distributed Power Systems
Green Electronics/ Appliances
Notebook Computers
Networking Systems
FPGA, DSP, ASIC Power Supplies
Typical Application
Rev1.0
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 1
9/4/2012
SE1484
3A 27V Synchronous Buck Converter
Functional Block Diagram
Ordering Information
Part Number
Marking Information
Package
Remarks
SE1484
YYWW means Production batch
XX=HF: Halogen Free.
SE1484-HF
PSOP8
YYWW-HF
Absolute Maximum Rating
Parameter
Maximum
-0.3 to 30
Units
V
Input Supply Voltage
SW Voltage
-0.3 to VIN + 0.3
VSW – 0.3 to VSW + 6
-0.3 to 5
V
BS Voltage
V
EN, FB, COMP Voltage
V
A
Continuous SW Current
Internally limited
20
Junction to Ambient Thermal Resistance (θJA)
Junction to Ambient Case Resistance (θJC)
PSOP-8 Power Dissipation
Maximum Junction Temperature
Storage Temperature Range
°C/W
°C/W
W
10
Internal limit
150
°C
-65 to 150
°C
Note: Exceeding these limits may damage the device. Even the duration of exceeding is very short.
Exposure to absolute maximum rating conditions for long periods may affect device reliability。
Rev1.0
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 2
9/4/2012
SE1484
3A 27V Synchronous Buck Converter
Recommended Operating Conditions
Parameter
Symbol
VIN
Value
Units
V
Supply Input Voltage
4.5 to +27
-20 to +125
Operating Junction Temperature
TJ
°C
Electrical Characteristics
VIN = 12V; TJ = 25°C; unless otherwise specified
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
V
Feedback Voltage
VFB
4.5V ≤ VIN ≤ 27V
0.9
0.925
1.1
90
0.95
Feedback Overvoltage Threshold
High-Side Switch-On Resistance*
Low-Side Switch-On Resistance*
High-Side Switch Leakage
Upper Switch Current Limit*
V
mΩ
mΩ
uA
A
70
VEN = VSW = 0V
Min Duty Cycle
From Drain to
Source
,
0.1
4.5
10
3.8
Lower Switch Current Limit*
1.2
A
COMP to Current Limit Trans conductance
Error Amplifier Trans conductance
Error Amplifier DC Gain*A
GCOMP
GEA
VEA
5.2
900
400
340
100
A/V
uA/V
V/V
KHz
KHz
%
ΔICOMP = ± 10uA
Switching Frequency
fSW
300
7.5
1.1
2.2
380
Short Circuit Switching Frequency
Minimum Duty Cycle
VFB = 0V
DMIN
Maximum Duty Cycle
DMAX
92
1.4
180
2.5
150
0.3
%
EN Shutdown Threshold Voltage
EN Shutdown Threshold Voltage Hysteresis
EN Lockout Threshold Voltage
EN Lockout Hysteresis
VEN Rising
2
V
mV
V
2.7
mV
uA
Supply Current in Shutdown
VEN = 0V
VEN = 3V,
VFB=1.0V
VEN Rising
3.0
1.5
4.4
IC Supply Current in Operation
1.3
mA
Input UVLO Threshold Rising
Input UVLO Threshold Hysteresis
Soft-start Current
UVLO
3.8
4.0
150
6
V
mV
uA
mS
℃
VSS = 0V
CSS =0.1uF
Soft-start Period
15
Thermal Shutdown Temperature*
Note: * Guaranteed by design, not tested
Hysteresis =25°C
155
Rev1.0
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 3
9/4/2012
SE1484
3A 27V Synchronous Buck Converter
Typical Application
SE1484 Circuit, 3.3V/3A output
SE1484 Circuit, 3.3V/3A output with EN function
Note: C2 is required for separate EN signal.
Rev1.0
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 4
9/4/2012
SE1484
3A 27V Synchronous Buck Converter
inductance value。
Applications
L based on the ripple current requirement:
Output Voltage Setting
Where VIN is the input voltage, VOUT is the output
voltage, fSW is the switching frequency, IOUTMAX is the
maximum output current, and KRIPPLE is the ripple
factor. Typically, choose KRIPPLE =~ 30% to correspond to
the peak-to-peak ripple current being ~30% of the
Figure1. Output Voltage Setting
maximum output current.
Figure 1 shows the connections for setting the output
voltage. Select the proper ratio of the two feedback
resistors R1 and R2 based on the output voltage.
Typically, use R2≈10KΩ and determine R1 from the
following equation:
With this inductor value, the peak inductor current is
IOUT•(1+KRIPPLE/2). Make sure that this peak inductor
current is less than the upper switch current limit. Finally,
select the inductor core size so that it does not saturate at
the current limit. Typical inductor values for various output
voltages are shown in Table 2.
Table 2. Typical Inductor Values
1V
1.2V
4.7
1.8V
10
2.5V
10
3.3V
10
5V
10
9V
22
VOUT
Table1－Recommended Resistance Values：
4.7
L(uH)
VOUT
1V
R1
R2
Input Capacitor
The input capacitor needs to be carefully selected to
maintain sufficiently low ripple at the supply input of the
converter. A low ESR Electrolytic (EC) capacitor is highly
recommended. Since large current flows in and out of this
capacitor during switching, its ESR also affects efficiency.
When EC cap is used, the input capacitance needs to be
equal to or higher than 68uF. The RMS ripple current
rating needs to be higher than 50% of the output current.
The input capacitor should be placed close to the VIN and
GND pins of the IC, with the shortest traces possible. The
input capacitor can be placed a little bit away if a small
parallel 0.1uF ceramic capacitor is placed right next to the
IC.
1.0KΩ
3.0KΩ
9.53KΩ
16.9KΩ
26.1KΩ
44.2KΩ
121KΩ
12KΩ
10KΩ
10KΩ
10KΩ
10KΩ
10KΩ
10KΩ
1.2V
1.8V
2.5V
3.3V
5V
12V
Inductor Selection
The inductor maintains a continuous current to the
output load. This inductor current has a ripple that is
dependent on the inductance value: higher inductance
reduces the peak-to-peak ripple current. The trade off
for high inductance value is the increase in inductor
core size and series resistance, and the reduction in
current handling capability. In general, select an
When Vin is >15V, pure ceramic Cin (* no EC cap) is
not recommended. This is because the ESR of a
ceramic cap is often too small, Pure ceramic Cin will work
Rev1.0
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 5
9/4/2012
SE1484
3A 27V Synchronous Buck Converter
with the parasite inductance of the input trace and The feedback loop of the IC is stabilized by the
forms a Vin resonant tank. When Vin is hot plug components at the COMP pin, as shown in Figure
in/out, this resonant tank will boost the Vin spike to 2. The DC loop gain of the system is determined by the
a very high voltage and damage the IC.
Output Capacitor
following equation:
The output capacitor also needs to have low ESR to
keep low output voltage ripple. In the case of The dominant pole P1 is due to CCOMP1:
ceramic output capacitors, RESR is very small and
does not contribute to the ripple. Therefore, a lower
capacitance value can be used for ceramic
capacitors. In the case of tantalum or electrolytic The second pole P2 is the output pole:
capacitors, the ripple is dominated by RESR
multiplied by the ripple current. In that case, the
output capacitor is chosen to have sufficiently low The first zero Z1 is due to RCOMP and CCOMP
ESR.
:
For ceramic output capacitors, typically choose of
about 22uF. For tantalum or electrolytic capacitors,
choose a capacitor with less than 50mΩ ESR.
Optional Schottky Diode
And finally, the third pole is due to RCOMP and CCOMP2 (if
CCOMP2 is used):
During the transition between high-side switch and
low-side switch, the body diode of the low side
power MOSFET conducts the inductor current. The The following steps should be used to compensate the
forward voltage of this body diode is high. An IC:
optional Schottky diode may be paralleled between
the SW pin and GND pin to improve overall
efficiency.
STEP1. Set the crossover frequency at 1/10 of the
switching frequency via RCOMP
:
Stability Compensation
but limit RCOMP to 10KΩ maximum. More than 10 KΩ is
easy to cause overshoot at power on.
STEP2. Set the zero fZ1 at 1/4 of the crossover
frequency. If RCOMP is less than 10KΩ, the equation for
CCOMP is:
Figure 2. Stability Compensation
CCOMP2 is needed only for high ESR output
capacitor.
Rev1.0
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 6
9/4/2012
SE1484
3A 27V Synchronous Buck Converter
STEP3. If the output capacitor’s ESR is high enough to cause a zero at lower than 4 times the crossover
frequency, an additional compensation capacitor CCOMP2 is required. The condition for using CCOMP2 is:
And the proper value for CCOMP2 is:
Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 such
as 100pF may improve stability against PCB layout parasitic effects
Table 4－ Component Selection Guide for Stability Compensation
Vin Range
Vout
(V)
1.0
1.2
1.8
2.5
3.3
5
Rcomp
(R3)(kΩ)
3.3
Ccomp
(C4)(nF)
5.6
Ccomp2
(C5)(pF)
none
Inductor
(uH)
4.7
Cout
(V)
5 – 12
5 – 15
5 – 15
5 – 15
5 – 15
5 – 15
5 – 12
5 – 15
5 – 23
5 – 27
5 – 27
5 – 27
3.9
4.7
none
4.7
22uFx2
5.6
3.3
none
10
8.2
2.2
none
10
Ceramic
10
2
none
10
10
3.3
none
10
1.0
1.2
1.8
2.5
3.3
5
4.7
10
470uF/
10
6.8
680
6.3V/120mΩ
Outline Drawing For PSOP8
Rev1.0
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 7
9/4/2012
SE1484
3A 27V Synchronous Buck Converter
联系方式：
北京思旺电子技术有限公司–中国总部
地址：中国北京市海淀区信息路 22 号上地科技综合楼 B 座二层
邮编：100085
电话:010-82895700/1/5
传真:010-82895706
Seaward Electronics Corporation – 台湾办事处
2F, #181, Sec. 3, Minquan East Rd,
Taipei, Taiwan R.O.C
电话: 886-2-2712-0307
传真: 886-2-2712-0191
Seaward Electronics Incorporated – 北美办事处
1512 Centre Pointe Dr.
Milpitas, CA95035, USA
电话: 1-408-821-6600
Rev1.0
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., • www.seawardinc.com.cn • Page 8
9/4/2012
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