AP1533

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AP1533

PWM CONTROL 1.8A STEP-DOWN CONVERTER

AP1533 Rev. 4 1 of 9 JULY 2009 DS31192 www.diodes.com Diodes Incorporated

Input voltage: 4V to 23V Output voltage: 0.8V to VCC

Output current: 1.8A up to peak 2A

Duty ratio: 0% to 99% PWM control

Oscillation frequency: 300KHz typ.

Soft-start like, Current limit and Enable function

Thermal Shutdown function

Built-in internal SW P-channel MOS

SOP-8L: Available in Green Molding Compound(No Br, Sb)

Lead Free Finish/ RoHS Compliant (Note 1)

AP1533 consists of step-down switching regulator with PWMcontrol. These devices include a reference voltage source,oscillation circuit, error amplifier, internal PMOS.

AP1533 provides low-ripple power, high efficiency, and excellenttransient characteristics. The PWM control circuit is able to varythe duty ratio linearly from 0 up to 99%. This converter alsocontains an error amplifier circuit as well as a soft-start circuit thatprevents overshoot at startup. An enable function, an over currentprotect function and a short circuit protect function are built inside,and when OCP or SCP happens, the operation frequency will bereduced from 300KHz to 50KHz. Also, an internal compensationblock 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 canfunction as step-down switching regulators. They serve as idealpower supply units for portable devices when coupled with the

SOP-8L mini-package, providing such outstanding features as lowcurrent consumption. Since this converter can accommodate aninput voltage up to 23V, it is also suitable for the operation via anAC adapter.

PC Motherboard

LCD Monitor

Graphic Card

DVD-Video Player

Telecom Equipment

ADSL Modem

Printer and other Peripheral Equipment

Microprocessor core supply

Typical Application Circui t

AP1533

+

-VSSEN

CC

RA

RB

D1*

FB

Vcc Output

CVcc

VOUT

=5V/1.8A

VIN

ROCSET

OCSET COUT

C IN

Optional

COCSET

CEN

REN

Option

100K

L1

33uH

6.8K

1.3K

3.3K

0.1uF

+

-

C

0.1uF 470uF470uF

0.1uF

* Suggested DIODES Power Schottky P/N: B340 series or PDS340.

VOUT

=VFB x (1+ RA /RB)

RB= 0.7K~5K ohm

Features General Description

Appl ications

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Block Diagram

Oscillation

Circuit

Reference

VoltageSource

PWM-Switched

ControlCircuit

+

-

VSSVEN

EN

90uA

OCSET

FB

VCC

Thermal

Shutdown

Output

Absolute Maximum Ratings

Symbol Parameter Rating Unit

ESD HBM Human Body Model ESD Protection 8 KV

ESD MM Machine Model ESD Protection 500 V

VCC VCCPin Voltage VSS- 0.3 to VSS+ 24 V

VFB Feedback Pin Voltage VSS- 0.3 to VCC V

VEN EN Pin Voltage VSS- 0.3 to VIN+ 0.3 V

VOUT Switch Pin Voltage VSS- 0.3 to VIN+ 0.3 V

PD Power Dissipation Internally limited mW

TJ Operating Junction Temperature Range -20 to +125oC

TST Storage Temperature Range -65 to +150oC

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 4 23 V

IOUT Output Current 0 1.8 A

TA Operating Ambient Temperature -25 85oC

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Electrical Characteristics

(VIN= 12V, TA = 25C, unless otherwise specified)Symbol Parameter Conditions Min Typ. Max Unit

VFB Feedback Voltage IOUT = 0.1A 0.784 0.8 0.816 V

IFB Feedback Bias Current IOUT = 0.1A - 0.1 0.5 A

ISHDNCurrent Consumption DuringPower Off

VEN = 0V - 10 - A

VOUT/ VIN

Line Regulation VIN = 5V~23V - 1 2 %

VOUT/ VOUT

Load Regulation IOUT = 0.1 to 1.8A - 0.2 0.5 %

fOSC Oscillation Frequency Measure waveform at SW pin 240 300 400 KHz

fOSC1Frequency of Current Limit orShort Circuit Protection

Measure waveform at SW pin - 50 - KHz

VIH EN Pin Input Voltage Evaluate oscillation at SW pin 2.0 - - VVIL Evaluate oscillation stop at SW pin - - 0.8

ISH EN Pin Input Leakage CurrentEN Pin High - 20 - A

ISL EN Pin Low - -10 - A

IOCSET OCSET Pin Bias Current -- 75 90 105 A

RDS(ON) Internal MOSFET RDS(ON)VIN=5V, VFB=0V - 110 150 mVIN=12V, VFB=0V - 80 110

EFFI EfficiencyVIN=12V, VOUT= 5VIOUT=1.8A

- 91 - %

TSHDN Thermal shutdown threshold - 150 - C

THYS Thermal shutdown hysteresis - 55 - C

JAThermal ResistanceJunction-to-Ambient

SOP-8L (Note 3) - 134 -oC/W

JC

Thermal Resistance

Junction-to-Case SOP-8L (Note 3) - 22 -

o

C/W

Notes: 3. Test condition: Device mounted on FR-4 PCB, 2x2, 2oz copper, minimum recommended pad layout, single side.For better thermal performance, larger copper pad for heatsink is needed.

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Typical Performance Characteristics (Continued)

VINvs. Frequency(VOUT=3.3V; IOUT=0.2A)

300

302

304

306

308

310

312

314

316

318

320

0 2 4 6 8 10 12 14 16 18 20 22 24VIN(V)

FOSC(kHz)

VINvs. VFB(VOUT=3.3V; IOUT=0.2A)

0.780

0.785

0.790

0.795

0.800

0.805

0.810

0.815

0.820

0 2 4 6 8 10 12 14 16 18 20 22 24VIN(V)

VFB(V)

Line Regulation(VOUT=3.3V; IOUT=0.2A)

3.00

3.05

3.10

3.15

3.20

3.25

3.30

3.35

3.40

0 2 4 6 8 10 12 14 16 18 20 22 24VIN(V)

VOUT(V)

Load Regulation(VIN=12V)

3.15

3.16

3.17

3.18

3.19

3.20

3.21

3.22

3.23

3.24

3.25

0 0.5 1 1.5 2IOUT(A)

VOUT(V)

Efficiency

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 0.5 1 1.5 2

IOUT (A)

Efficiency(%)

VOUT=3.3V

VOUT=5V

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Typical Performance Characteristics (Continued)

VOUTRipple( VIN= 12V; VOUT= 3.3V; IOUT= 0.1A )VOUT Ripple(VIN= 12V; VOUT= 3.3V; IOUT= 1.8A )

Test Circuit

A

FBVCC

VSS

EN

open

open

FB

EN

+

-

Oscillation

OUTPUT OUTPUTA

FB

EN

+

-+

-

V

OUTPUT

OCSETOCSET

OCSET

Enable function test Feedback function test

Operation function test

VCC

VCC

VSS

VSS

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Functional Description

PWM Contro lThe AP1533 is a DC/DC converter that employs pulse widthmodulation (PWM) scheme. Its pulse width varies in the range of0% to 99%, based on the output current loading. The output

ripple voltage caused by the PWM high frequency switching caneasily be reduced through an output filter. Therefore, thisconverter provides a low ripple output supply over a broad rangeof input voltage & output current loading

Under Voltage LockoutThe under voltage lockout circuit of the AP1533 assures that thehigh-side MOSFET driver remains in the off state whenever thesupply voltage drops below 3.3V. Normal operation resumes

once VCCrises above 3.5V.

Current Li mit Protection

The current limit threshold is set by external resistor R OCSET

connected from VCC supply to OCSET pin. The internal sink

current IOCSET (90A typical) across this resistor sets the voltage

at OCSET pin. When the PWM voltage is less than the voltage atOCSET, an over-current condition is triggered.

The current limit threshold is given by the following equation:

RIRI OCSETOCSETDS(ON)PEAK=

2

)I(+> II OUT(MAX)PEAK

where,

IN

OUTOUTIN

V

V

Lfs

VVI

=

IPEAK is the output peak current; RDS (ON) is the MOSFET ON

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

inductor value will affect the ripple current I.

The above equation is recommended for input voltage range of5V to 18V. For input voltage lower than 5V or ambient

temperature over 100C, higher ROCSET is recommended.

The recommended minimum ROCSETvalue is summarized below:

VIN(V) VOUT(V) ROCSET ()

4 0.8 3.9K

5 3.3 3.3K

12 5 3.3K

18 12 3.3K

23 12 4.7K

The maximum ROCSETvalue should not exceed AP1533 maximumcurrent output.

Inductor SelectionFor most designs, the operation range with inductors is from22H to 33H. The inductor value can be derived from thefollowing equation:

IN

OUTOUTIN

V

V

fs

VVL

=

I

Where IL is inductor Ripple Current. Large value inductors lower

ripple current and small value inductors result in high ripplecurrent. Choose inductor ripple current approximately 15% of the

maximum load current 1.8A, IL=0.27A. The DC current rating of

the inductor should be at least equal to the maximum load currentplus half the ripple current to prevent core saturation(1.8A+0.135A).

Input Capacitor Selection

This capacitor should be located close to the IC using short leadsand the voltage rating should be approximately 1.5 times themaximum input voltage. The RMS current rating requirement forthe input capacitor of a buck regulator is approximately 12 the

DC load current. A low ESR input capacitor sized for maximumRMS current must be used. A 470F low ESR capacitor for mostapplications is sufficient.

Output Capacitor SelectionThe output capacitor is required to filter the output voltage andprovides regulator loop stability. The important capacitorparameters are the 100KHz Equivalent Series Resistance (ESR),the RMS ripples current rating, voltage rating and capacitancevalue. For the output capacitor, the ESR value is the mostimportant parameter. The output ripple can be calculated fromthe following formula.

ESRIV LRIPPLE =

The bulk capacitors ESR will determine the output ripple voltageand the initial voltage drop after a high slew-rate transient.

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

PCB Layout Guide

If you need low TC& TJor large PD(Power Dissipation), The dual

SW pins(5& 6) and Vss pins(7& 8)on the SOP-8L package areinternally connected to die pad, The evaluation board should beallowed for maximum copper area at output (SW) pins.

1. Connect FB circuits as closely as possible and keep away

from inductor flux for pure VFB.

2. Connect input capacitor to Vcc and Vss pin as closely aspossible to get good power filter effect.

3. Connect ROCSET to Vcc and OCSET pin as closely aspossible.

4. Connect ground side of the input capacitor & Schottky &output capacitor as closely as possible and use groundplane for best performance.

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Marking Information

(1) SOP-8L( Top View )

AP1533YYWWX X

Logo

Part Number

58

41

WW : Week : 01~52; 52YY : Year : 08, 09,10~G : Green

X : Internal Coderepresents 52 and 53 week

Package Information ( All Dimensions in mm )

(1) Package Type: SOP-8L

1.27typ 0.3/0.5

7~9

4.85/4.95

3.8

5/3.9

5

5.9

0/6.1

0

0.1

5/0.2

5

7~9

0.62/0.820.1

0/0.2

0Gauge Plane0

.254

Seating Plane

0.35max. 45

Detail "A"

Detail "A"

1.3

0/1.5

0

1.7

5max.

Land Pattern Recommendation(Unit: mm)

6x-1.27

8x-1.55

8x-0.60

5.4

0/8

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AP1533