Diodes AP1538 User Manual

AP1538

18V 3A 300KHz BUCK CONVERTER

Features

• Input voltage : 3.6V to 18V

• Output voltage : 0.8V to V

• Output current : up to 3A

• Duty ratio: 0% to 99% PWM control

• Oscillation frequency: 300KHz typical

• Soft-start like, Current limit and Enable function

• Thermal Shutdown function

• Built-in internal SW P-channel MOS

• SOP-8L and SOP-8L-DEP: Available in “Green”

Molding Compound (No Br, Sb)

• Lead Free Finish / RoHS Compliant (Note 1)

CC

Applications

• PC Motherboard

• LCD Monitor

• Graphic Card

• DVD-Video Player

• Telecom Equipment

• ADSL Modem

• Printer and other Peripheral Equipment

• Microprocessor core supply

General Description

AP1538 consists of step-down switching regulator with PWM control. These devices include a reference voltage source, oscillation circuit, error amplifier, internal PMOS. AP1538 provides low-ripple power, high efficiency, and excellent transient characteristics. The PWM control circuit is able to vary the duty ratio linearly from 0 up to 99%. This converter also contains an error amplifier circuit as well as a soft-start circuit that prevents overshoot at startup. An enable function, an over current protect function and a short circuit protect function are built inside, and when OCP or SCP happens, the operation frequency will be reduced from 300KHz to 50KHz. Also, an internal compensation block is built in to minimum external component count. With the addition of an internal P-channel Power MOS, a coil, capacitors, and a diode connected externally, these ICs can function as step-down switching regulators. They serve as ideal power supply units for portable devices when coupled with the SOP-8L and SOP-8L-DEP mini-packages, providing such outstanding features as low current consumption. Since this converter can accommodate an input voltage up to 18V, it is also suitable for the o peration via an AC adapter.

Typical Application Circuit

V

= 5V/3A

+

-

OUT

C

0.1uF

+

C

OUT

470uF

-

***

V

IN

R

OCSET

Option

3K

C

IN

470uF

CVcc

0.1uF

Notes: * Typical feedback compensation (Cc): 5600pF.

** Suggested DIODES Power Schottky P/N: B540 series or PDS540.

*** Suggested C

R 100K

C

0.1uF

C

EN

OCSET

Vcc

AP 1538

OCSET

EN

V

OUT

=

= 0.7K~5K ohm

R

B

for V

OUT

x (

1+

FB

< 1V; 680uF.

Output

FB

V

SS

R

A

/R

)

B

L1

22uH

Cc

Option*

D1**

R

A

6.8K

R

B

1.3K

AP1538 Rev. 5 1 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

Ordering Information

AP1538

18V 3A 300KHz BUCK CONVERTER

AP 1538 XXX G - 13

Package Packing

S : SOP-8L

SDP : SOP-8L-DEP

Device

AP1538SG-13 S SOP-8L 2500/Tape & Reel -13 AP1538SDPG-13 SDP SOP-8L-DEP 2500/Tape & Reel -13

Notes: 1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at

2. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf.

http://www.diodes.com/products/lead_free.html

Package

Code

Packaging

(Note 2)

Green

G : Green

13 : Tape & Reel

13” Tape and Reel

Quantity Part Number Suffix

Pin Assignments

(1) SOP-8L (2) SOP-8L-DEP (Dual Exposed Pads)

( Top View )

FB

1

Vss

8

FB

1

Vss

8

1

EN

2

Vss

7

EN

2

Vss

7

OCSET

3

6

Output

OCSET

3

6

Output

2

4

V

4

V

CC

Notes: 3. Exposed pad 1 is connected to VSS and exposed pad 2 is connected to Output. The board layout for exposed pads needs to be considered to

AP1538 Rev. 5 2 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

avoid short circuit.

5

Output

CC

(Note 3)

5

Output

18V 3A 300KHz BUCK CONVERTER

Pin Descriptions

Pin Name

FB 1 Feedback pin

EN 2

OCSET 3 Add an external resistor to set max output current

VCC 4 IC power supply pin

Pin No.

Power-off pin H: Normal operation (Step-down operation) L: Step-down operation stopped (All circuits deactivated)

Description

AP1538

Output 5, 6

VSS 7, 8 GND Pi n

Switch Pin. Connect external inductor/diode here. Minimize tra ce area at this pin to red uc e EMI

Block Diagram

Output

Oscillation

Circuit

Vcc

PWM-Switched Control Circuit

Thermal

Shutdown

EN

AP1538 Rev. 5 3 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

Reference Voltage

Sourc e w i th S o ft Start

+

-

90uA

OCSET

FB

VssV

AP1538

18V 3A 300KHz BUCK CONVERTER

Absolute Maximum Ratings

Symbol Parameter Rating Unit

ESD HBM Human Body Model ESD Protection 5.5 KV

ESD MM Machine Model ESD Protection 200 V

VCC VCC Pin Voltage VSS - 0.3 to VSS + 20 V VFB Feedback Pin Voltage VSS - 0.3 to VCC V VEN EN Pin Voltage VSS - 0.3 to VCC V

V

Switch Pin Voltage VSS - 0.3 to VCC V

OUT

PD Power Dissipation Internally limited mW

TJ Operating Junction Temperature Range -40 to +125

T

Storage Temperature Range -65 to +150

ST

Caution: The absolute maximum ratings are rated values exceeding which the product could suffer physical damage.

These values must therefore not be exceeded under any conditions.

Recommended Operating Conditions

Symbol Parameter Min Max Unit

VIN Input Voltage (Note 4) 3.6 18 V

I

Output Current 0 3 A

OUT

TA Operating Ambient Temperature -20 +85

Notes: 4. For the operations in low input voltage, AP1538 can tolerate down to 3.6V but max output current loading will be less than 3A. For nominal

applications in such low input voltage range, especially lower than 4V, a higher ROCSET with larger heat sink is recommended.

o

C

o

C

o

C

AP1538 Rev. 5 4 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

A

AP1538

18V 3A 300KHz BUCK CONVERTER

Electrical Characteristics

IN = 12V, T

(V

Symbol Parameter Conditions Min Typ. Max Unit

VFB Feedback Voltage I

IFB Feedback Bias Current I

I

SHDN

∆V

OUT

/ VIN

∆V

OUT

/ V

OUT

f

Oscillation Frequency Measure waveform at SW pin 240 300 400 KHz

OSC

f

OSC1

VIH

VIL Evaluate oscillation stop at SW pin - - 0.8 ISH ISL EN Pin Low - -10 - µA

I

OCSET

R

DS(ON)

EFFI Efficiency

T

SHDN

T

Thermal shutdown hysteresis - 55 - °C

HYS

θ

JC

Notes: 5. Test condition for SOP-8L and SOP-8L-DEP: Devices mounted on 2oz copper, minimum recommended pad layout on top & bottom layer with

AP1538 Rev. 5 5 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

= 25°C, unless otherwise specified)

A

= 0.1A 0.784 0.8 0.816 V

OUT

= 0.1A - 0.1 0.5 µA

OUT

Current Consumption During Power Off

Line Regulation V

Load Regulation I

Frequency of Current Limit or Short Circuit Protection

EN Pin Input Voltage EN Pin Input Leakage Current

V

= 0V - 10 - µA

EN

= 5V~18V - 1 2 %

IN

= 0.1 to 3A - 0.2 0.5 %

OUT

Measure waveform at SW pin - 50 - KHz Evaluate oscillation at SW pin 2.0 - -

V

EN Pin High - 20 - µA

OCSET Pin Bias Current -- 75 90 105 µA

Internal MOSFET R

DS(ON)

IN

VIN=12V, VFB=0V - 70 V

=12V, V

IN

I

OUT

=3

OUT

= 5V

- 92 - %

mΩ

=5V, VFB=0V - 110 -

V

Thermal shutdown threshold - 150 - °C

Thermal Resistance Junction-to-Case

thermal vias, double sided FR-4 PCB.

SOP-8L (Note 5) - 24 SOP-8L-DEP (Note 5) - 26 -

o

C/W

AP1538

18V 3A 300KHz BUCK CONVERTER

Typical Performance Characteristics

VIN v s. Frequenc y

(V

= 3.3V, I

326

OUT

324 322 320 318 316

(kHz)

OSC

314

F

312 310 308 306

0 2 4 6 8 10 12 14 16 18

V

OUT

IN

= 0.2A)

(V)

0.820

0.815

0.810

0.805

(V)

0.800

FB

V

0.795

0.790

0.785

0.780 024681012141618

Line Regulation

(V

= 3.3V, I

3.40

OUT

3.35

3.30

3.25

(V)

3.20

OUT

V

3.15

3.10

3.05

3.00 024681012141618

= 0.2A)

OUT

3.35

3.34

3.33

3.32

3.31

(V)

3.30

OUT

3.29

V

3.28

3.27

3.26

3.25

(V)

V

IN

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Efficiency

(V

= 12V)

100

90 80 70 60 50 40

Efficiency (%)

30 20 10

0

0.0 1.0 2.0 3.0

IN

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

Current Limit (A)

VOUT=3.3V VOUT=5V

3.5

3.0

2.5 0 2 4 6 8 10 12 14 16 18

I

(A)

OUT

AP1538 Rev. 5 6 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

VIN vs. V

(V

OUT

= 3.3V, I

FB

= 0.2A)

OUT

(V)

V

IN

Load Regulation

(V

= 12V)

IN

I

(A)

OUT

Switch Current Limit

(TA = 25C)

V

(V)

IN

ROCSET=6.8k ROCSET=3.9k

V

18V 3A 300KHz BUCK CONVERTER

Typical Performance Characteristics (Continued)

Current Lim i t vs. Temperat ure

9.0

8.5

8.0

7.5

7.0

6.5

6.0

5.5

Current Limit (A)

5.0

4.5

4.0

-25 0 25 50 75 100

(VIN=12V, R

Ambient Temperature (C)

OCSET

=6.8k)

AP1538

Ripple

(V

IN

= 12V, V

OUT

= 3.3V, I

OUT

Load Transient Response

(V

= 12V, V

IN

= 3.3V, I

OUT

= 0.1A)

OUT

= 0.1~3A)

OUT

Ripple

(V

IN

= 12V, V

OUT

= 3.3V, I

OUT

= 3.0A)

AP1538 Rev. 5 7 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

Test Circuit

18V 3A 300KHz BUCK CONVERTER

open

OUTPUT OUTPUT

CC

OCSET

A

EN

V

SS

Enable function test Feedback function test

open

FBV

Oscillation

A

V

CC

+

-

OCSET EN

V

AP1538

FB

SS

V

CC

+

-

OCSET EN

Operation fun c tion test

OUTPUT

FB

V

SS

+

-

AP1538 Rev. 5 8 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

AP1538

18V 3A 300KHz BUCK CONVERTER

Functional Description

PWM Control

The AP1538 is a DC/DC converter that employs pulse width modulation (PWM) scheme. Its pulse width varies in the range of 0% to 99%, based on the output current loading. The output ripple voltage caused by the PWM high frequency switching can easily be reduced through an output filter. Therefore, this converter provides a low ripple output supply over a broad range of input voltage & output current loading

Under Voltage Lockout

The under voltage lockout circuit of the AP1538 assures that the high-side MOSFET driver remains in the off state whenever the supply voltage drops below 3.3V. Normal operation resumes once V

Current Limit Protection

The current limit threshold is set by external resistor R connected from V current I at OCSET pin. When the PWM voltage is less than the voltage at

OCSET, an over-cur rent condition is trigg ered. The current limit threshold is given by the following equation:

where,

I resistance; F inductor value will affect the ripple current ΔI.

The above equation is recommended for input voltage range of 5V to 18V. For input voltage lower than 5V or ambient temperature over 100°C, higher R

The recommended minimum R

rises above 3.5V.

CC

supply to OCSET pin. The internal sink

CC

(90uA typical) across this resistor sets the voltage

OCSET

×=×

RIRI

OCSETOCSETDS(ON)PEAK

)I(Δ

II

OUT(MAX)PEAK

−

I ×

=Δ

is the output peak current; R

PEAK

V

OUT

(V)

0.8 4.7K 3.0K 3.3K

1.0 5.6K 3.0K 3.9K

1.2 5.6K 3.0K 3.9K

1.8 5.6K 3.0K 3.9K

2.5 5.6K 3.0K 3.9K

3.3 5.6K 3.0K 3.9K

5.0 N/A 3.0K 4.7K

is the PWM frequency (300KHz typical). Also, the

S

5V 12V 18V

+>

VV

Lfs

×

OCSET

VIN (V)

2

V

OUTOUTIN

V

IN

is the MOSFET ON

DS (ON)

is recommended.

OCSET

value is summarized below:

OCSET

AP1538 Rev. 5 9 of 13 OCTOBER 2009 DS31451 www.diodes.com © Diodes Incorporated

Inductor Selection

For most designs, the operates with inductors of 22µH to 33µH. The inductor value can be derived from the following equation:

VV

L ×

Where ΔI ripple current and small value inductors result in high ripple current. Choose inductor ripple current approximately 15% of the maximum load current 3A, ∆I the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (3A+0.225A).

Input Capacitor Selection This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5 times the maximum input volta ge. The RMS current rati ng requirement for the input capacitor of a buck regulator is approximately 1⁄2 the DC load current. A low ESR input capacitor sized for maximum RMS current must be used. A 47 0µF low ESR c apacitor for most applications is sufficient.

Output Capacitor Selection The output capacitor is required to filter the output voltage and provides regulator loop stability. The important capacitor parameters are the 100KHz Equivalent Series Resistance (ESR), the RMS ripples current rating, voltage rating and capacitance value. For the output capacitor, the ESR value is the most important parameter . The output ripple can be calculated fro m the following formula.

The bulk capacitor’s ESR will determine the output ripple voltage and the initial voltage drop after a high slew-rate transient.

An aluminum electrolytic capacitor's ESR value is related to the capacitance and its voltage rating. In most case, higher voltage electrolytic capacitors have lower ESR values. Most of the time, capacitors with much higher voltage ratings may be needed to provide the low ESR values required for low output ripple v oltage .

PCB Layout Guide If you need low T SW pins(5& 6) and Vss pins(7& 8)on the SOP-8L package are internally connected to die pad, The evaluation board should be allowed for maximum copper area at output (SW) pins.

1. Connect FB circuits (R

2. Connect C3 to Vcc and Vss pin as closely as possible to get

3. Connect R4 to Vcc and OCSET pin as closely as possible.

4. Connect ground side of the C2 & D1 & C4 as closely as

is inductor Ripple Current. Large value inductors lower

L

& TJ or large PD (Power Dissipation), The dual

C

keep away from inductor flux for pure V good power filter effect.

possible and use ground plane for best performance.

−

=

fs

L

, R2, C1) as closely as possible and

1

V

OUTOUTIN

I

ΔIV

V

ESR

×=

LRIPPLE

FB

IN

.

Δ×

=0.45A. The DC current rating of

V

Functional Description (Continued)

Keep the gap of exposed pads from short circuit.

Top Side Layout Guid e

AP1538

18V 3A 300KHz BUCK CONVERTER

Recommended exposed-pads gap: 30~40mil (0.75~1mm)

Use vias to conduct the heat into the backside of PCB layer. The heat si nk at output (SW) pins should be allowed for maximum solder-painted area.

Bottom Side Layout Guide

Brown: IC exposed pads. Red: recommended layout. Reference pads layout dimension: Output: 90 x 50 mil

ss: 90 x 60 mil

Functional Description (Continued)

V

IN

Vcc

Output

AP1538

18V 3A 300KHz BUCK CONVERTER

L1

V

OUT

R4

C2

C3

Marking Information

(1) SOP-8L

Logo

Part Number

C7

Option

R5

C6

Figure: Layout numbering comparison.

OCSET

EN

AP1538

FB

V

SS

( Top View )

8

5

G : Green

: Year : 08, 09,10~

AP1538

YY

WW X

X

YY WW : Week : 01~52; 52

: Internal Code

X

C1

Option

D1

R1

R2

+

-

C8

C4

-

represents 52 and 53 week

41

(2) SOP-8L-DEP

( Top View )

X

5

G : Green

: Year : 08, 09,10~

YY

WW

: Week : 01~52; 52

E

X

represents 52 and 53 week

: Internal Code

Logo

Part No.

8

AP1538

WW X

YY

SOP-8L-DEP

41

Package Information ( All Dimensions in mm )

(1) P ackage type: SOP-8L

0.254

3.85/3.95

5.90/6.10

0.10/0.20

Detail "A"

0.62/0.82

Gauge Plane Seating Plane

AP1538

18V 3A 300KHz BUCK CONVERTER

7°~9°

1.30/1.50

1.27typ

8x-0.60

6x-1.27

8x-1.55

Land Pattern Recommendation

0.3/0.5

4.85/4.95

5.4

(Unit: mm)

(2) P ackage type: SOP-8L-DEP

8

1

)

e

d

i

s

l

al

(

°

9

1

.

0

R

2.05Typ.

0.685

1

2.15Typ.

4.85/4.95

0.20

0.3/0.5

1.27Typ.

5

4

1.15Typ.

4

3.85/3.95

1.4/1.5

EXPOSED PAD

C

L

0.9

5.90/6.10

0.35Typ.

1.63Max.

0.35max.

7°~9°

45°

Detail "A"

0.15/0.25

1.75max.

0°/8°

C

L

1.8 1. 8

0.951.65

8

1.0

C

L

5.4

2.35

1

8x-0.60

4

5

°

View"A"

0.15/0.25

0/0.13

View"A"

0

8

/

°

0.254

0.62/0.82

5

8x-1.55

EXPOSED PAD

Top View

Land Pattem Recommendation (Unit: mm)

4

6x-1.27

Gauge Plane Seating Plane

58

1.7 1.7

C

L

Bottom view

0.713

AP1538

18V 3A 300KHz BUCK CONVERTER

DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BU T NOT LIMI TED TO, T HE IMPLIE D WARRANT IES OF ME RCHANTABILIT Y AND FI TNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).

Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arisi ng out of the application or use of this document or any product descr ibed herein; neither does Diode s Incorporated convey any license under its patent or trademark rig hts, nor the rights of othe rs. Any Customer or user of this docume nt or products described herein in such applications shall assume all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated website, harmless against all damages.

Diodes Incorporat ed does not warrant or accept a ny liabil ity whatsoeve r in respect of any p roducts purc hase d through unau thori zed sales channel. Should Customers purch ase or use Diodes Incorpo rated products for an y unintended or unau thorized applic ation, Customers sh all indemnify and hold Dio des Inc orporated and its re presen tatives harmle ss against all cla ims, d amages, expens es, a nd attor ney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.

Products described here in may be covered by one or more Unit ed States, i nternationa l or foreign patents p ending. Product n ames and markings noted herein may also be covered by one or more United States, i nte rn ational or foreign trademar ks.

Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Execut i ve Off icer of Diodes Incorporat e d. As us e d herei n:

A. Life support devices or systems are devices or systems which:

1. are intended to implant into the body, or

2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user.

B. A critical componen t is any component in a life s upport devi ce or system whose failure to perfo rm can be reaso nably expec ted

to cause the failure of the life support device or to affect its safety or effectiveness.

Customers repres ent that th ey have all necessar y expertis e in th e safety a nd regul ator y ramific ations of t heir lif e support devic es or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstandin g any devices- or systems-related inform ation or support that may be provided by Diodes Incorporated. Further, Customers must full y indemnify Diode s Incorporat ed and its represent atives ag ainst any damages ari sing out of th e use of Diodes Incorporated products in such safety-critical, life support devices or systems.

www.diodes.com

IMPORTANT NOTICE

LIFE SUPPORT