SE1482 [SEAWARD]

2A 27V Synchronous Buck Converter;


型号：	SE1482
厂家：	Seaward Electronics Inc.
描述：	2A 27V Synchronous Buck Converter
文件：	总9页 (文件大小：698K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

SE1482

2A 27V Synchronous Buck Converter

General Description

Features

The SE1482 is a monolithic synchronous buck

regulator. The device integrates 95 mΩ MOSFETS

that provide 2A continuous load current over



2A Output Current

Wide 4.5V to 27V Operating Input Range

Output Adjustable from 0.925V to 0.8Vin

Up to 96% Efficiency

wide operating input voltage of

4.5V

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

Pin Configuration

Input Under Voltage Lockout

Package： SOP-8/PSOP-8

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.

9/4/2012

SE1482

2A 27V Synchronous Buck Converter

Functional Block Diagram

Ordering Information

Part Number

Marking Information

Package

SOP8

Remarks

YYWW means Production batch

XX=HF: Halogen Free.

SE1482

SE1482-HF

YYWW-HF

PSOP8

Pin Descriptions

Pin Num Pin

Descriptions

Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver.

Connect a 0.01uF capacitor between BS and SW.

Input Supply. Bypass this pin to GND with a low ESR capacitor. See Input Capacitor in

the Application Information section.

Vin

Switch Output. Connect this pin to the switching end of the inductor.

GND Ground.

Feedback Input. The voltage at this pin is regulated to 0.925V. Connect to the resistor

divider between output and ground to set output voltage.

COMP Compensation Pin. See Stability Compensation in the Application Information section.

Enable Input. When higher than 2.7V, this pin turns the IC on. When lower than 1.1V,

this pin turns the IC off. Output voltage is discharged when the IC is off. This pin should

not be left open. Recommend to put a 100KΩ pull up resistor to Vin for start up.

Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS

to GND to set the soft-start period. A 0.1uF capacitor sets the soft-start period to 15ms.

To disable the soft-start feature, leave SS unconnected.

Rev1.0

Preliminary and all contents are subject to change without prior notice.

9/4/2012

SE1482

2A 27V Synchronous Buck Converter

Absolute Maximum Rating

Parameter

Maximum

-0.3 to 30

Units

Input Supply Voltage

SW Voltage

-0.3 to VIN + 0.3

VSW – 0.3 to VSW + 6

-0.3 to 5

BS Voltage

EN, FB, COMP Voltage

Continuous SW Current

Junction to Ambient Thermal Resistance (θJA)

PSOP-8 Power Dissipation

Maximum Junction Temperature

Storage Temperature Range

Internally limited

°C/W

Internal limit

150

°C

-65 to 150

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。

Recommended Operating Conditions

Parameter

Symbol

V_IN

Value

Units

Supply Input Voltage

4.5 to +27

-20 to +125

Operating Junction Temperature

T_J

°C

Electrical Characteristics

V_IN= 12V; T_J= 25°C; unless otherwise specified

Parameter

Symbol

Conditions

Min

Typ

0.925

1.1

Max

Unit

Feedback Voltage

V_FB

4.5V ≤ V_IN≤ 27V

0.9

0.95

Feedback Overvoltage Threshold

High-Side Switch-On Resistance*

Low-Side Switch-On Resistance*

High-Side Switch Leakage

mΩ

V_EN= V_SW= 0V

Min Duty Cycle

Upper Switch Current Limit*

COMP to Current Limit Trans conductance

Error Amplifier Trans conductance

Error Amplifier DC Gain*A

2.7

3.5

3.3

G_COMP

G_EA

V_EA

A/V

uA/V

V/V

KHz

ΔI_COMP= ± 10uA

920

480

340

120

Switching Frequency

f_SW

Short Circuit Switching Frequency

Maximum Duty Cycle

V_FB= 0V

D_MAX

V_FB= 0.8V

Minimum On Time*

220

1.4

EN Shutdown Threshold Voltage

EN Shutdown Threshold Voltage Hysteresis

V_ENRising

1.1

180

Rev1.0

Preliminary and all contents are subject to change without prior notice.

9/4/2012

SE1482

2A 27V Synchronous Buck Converter

EN Lockout Threshold Voltage

EN Lockout Hysteresis

2.2

2.5

130

0.3

2.7

Supply Current in Shutdown

V_EN= 0V

V_EN= 3V,

V_FB=1.0V

V_ENRising

IC Supply Current in Operation

1.3

1.5

4.4

Input UVLO Threshold Rising

Input UVLO Threshold Hysteresis

Soft-start Current

UVLO

3.8

4.05

100

V_SS= 0V

C_SS=0.1uF

Hysteresis

=25°C

Soft-start Period

Thermal Shutdown Temperature*

160

℃

Note: * Guaranteed by design, not tested

Typical Application

SE1482 Circuit, 3.3V/2A output

SE1482 Circuit, 3.3V/2A 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.

9/4/2012

SE1482

2A 27V Synchronous Buck Converter

select an inductance value。

Applications

L based on the ripple current requirement:

Output Voltage Setting

Where VIN is the input voltage, VOUT is the output voltage,

f_SWis 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 maximum output current.

With this inductor value, the peak inductor current is

Figure1. Output Voltage Setting

Figure 1 shows the connections for setting the output I_OUT•(1+K_RIPPLE/2). Make sure that this peak inductor current is

voltage. Select the proper ratio of the two feedback less than the upper switch current limit. Finally, select the

resistors R1 and R2 based on the output voltage. inductor core size so that it does not saturate at the current

Typically, use R2≈10KΩ and determine R1 from the limit. Typical inductor values for various output voltages are

following equation:

shown in Table 2.

Table 2. Typical Inductor Values

1.2V

1.8V

2.5V

3.3V

V_OUT

4.7uH 4.7uH 10uH 10uH 10uH

10uH 22uH

Table1－Recommended Resistance Values：

VOUT

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.

1.0KΩ

3.0KΩ

9.53KΩ

16.9KΩ

26.1KΩ

44.2KΩ

121KΩ

12KΩ

10KΩ

1.2V

1.8V

2.5V

3.3V

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.

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,

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 with the parasite

Rev1.0

Preliminary and all contents are subject to change without prior notice.

9/4/2012

SE1482

2A 27V Synchronous Buck Converter

inductance of the input trace and forms a Vin The feedback loop of the IC is stabilized by the

resonant tank. When Vin is hot plug in/out, this components at the COMP pin, as shown in Figure

resonant tank will boost the Vin spike to a very high 2. The DC loop gain of the system is determined by the

voltage and damage the IC.

following equation:

Output Capacitor

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 C_COMP1:

ceramic output capacitors, R_ESRis 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 R_ESR

multiplied by the ripple current. In that case, the

output capacitor is chosen to have sufficiently low The first zero Z1 is due to R_COMPand C_COMP

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 R_COMPand C_COMP2(if

C_COMP2is 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 R_COMP

Stability Compensation

but limit R_COMPto 10KΩ maximum. More than 10 KΩ is

easy to cause overshoot at power on.

STEP2. Set the zero f_Z1at 1/4 of the crossover

frequency. If R_COMPis less than 10KΩ, the equation for

C_COMPis:

Figure 2. Stability Compensation

C_COMP2is needed only for high ESR output

capacitor.

Rev1.0

Preliminary and all contents are subject to change without prior notice.

9/4/2012

SE1482

2A 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 C_COMP2is required. The condition for using C_COMP2is:

And the proper value for C_COMP2is:

Though C_COMP2is unnecessary when the output capacitor has sufficiently low ESR, a small value C_COMP2such

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

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 – 12

5 – 15

5 – 23

5 – 27

3.9

4.7

none

4.7

22uFx2

5.6

3.3

none

8.2

2.2

none

Ceramic

none

3.3

none

1.0

1.2

1.8

2.5

3.3

4.7

470uF/

6.8

680

6.3V/120mΩ

Rev1.0

Preliminary and all contents are subject to change without prior notice.

9/4/2012

SE1482

2A 27V Synchronous Buck Converter

Outline Drawing For SOP8

D I M E N S I O N S

I N C H E S

D I M

M I N M A X M I N M A X

0 . 0 5 302. 0 6 8 81 . 3 5 1 . 7 5

0.0040 0.0098

0.0130 0.0200

0 . 0 5 0 B S

0.0075 0.0098

0.1890 0.1968

0.2284 0.2440

0.1497 0.1574

0.10

0.33

0.25

0.51

1 . 2 7 B S C

0.19

0.25

5.00

6.20

4.00

4.80

5.80

3.80

Outline Drawing For PSOP8

Rev1.0

Preliminary and all contents are subject to change without prior notice.

9/4/2012

SE1482

2A 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.

9/4/2012

SE1482 [SEAWARD]

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