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

EN

OCSET

Vcc

AP 1538

OCSET

EN

V

V

OUT

=

= 0.7K~5K ohm

R

B

for V

OUT

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 )

( 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

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