Diodes AP5726 User Manual

AP5726

WHITE LED STEP-UP CONVERTER

Description

The AP5726 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive 2 ~ 6 LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminates the need for ballast resistors. For driving higher number of LEDs, AP5726 also supports a single feedback of parallel connected multiple strings of equal number of LEDs.

The AP5726 switches at 1.2MHz that allows the use of tiny external components. A low 0.31V feedback voltage minimizes power loss in the current setting resistor for better efficiency.

Features

• High efficiency: 84% typical

• Fast 1.2MHz switching frequency

• Current limit and UVLO protections

• Internal Thermal Shutdown

• Internal Over Voltage Protection

• Integrated soft-start function

• SOT26, TSOT23-6 and DFN2020C-6: Available in “Green” Molding Compound (No Br, Sb)

• Lead Free Finish/ RoHS Compliant (Note 1)

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

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

Pin Assignments

(Top View)

SW

GND

FB

1

2

3

VIN

6

5

OVP

7

4

EN

SOT26 / TSOT23-6

Applications

• Cellular Phones

• PDAs, Hand help Computers

• Digital Cameras

• MP3 Players

• GPS Receivers

SW

V

IN

OVP

DFN2020C-6

(Top View)

1

2

3

6

GND

5

FB

4

EN

Typical Application Circuit

V

IN

OFFON

PWM Dimming

AP5726

Document number: DS31845 Rev. 3 - 2

L1

22uH

C

IN

D1

1uF

V

AP5726

EN

IN

SW

OVP

FB

GND

Figure 1. Typical Application Circuit

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R

15

SET

2~6 LEDs

C

OUT

1uF

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WHITE LED STEP-UP CONVERTER

Pin Descriptions

Pin Name Description

SW Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI.

GND GND pin.

FB

EN

OVP Output Voltage detect pin for over voltage protection.

VIN Input Supply Pin. Must be locally bypassed with 1μF or 2.2μF to reduce input noise.

Functional Block Diagram

Feedback Pin. Reference voltage is 0.31V. Connect cathode of lowest LED and a sense resister here. Calculate resistor value according to the formula: R

= 0.31V / ILED

SET

Converter On/Off Control Input. A high input at EN turns the converter On, and a low input turns it off. If On/Off control is not needed, connect EN to the input source for automatic startup. The EN pin cannot be left floating.

OVP

5

AP5726

1

Comparator

-

A2

+

Rc

A1

-

+

FB

3

V

6

IN

REF

0.31V

Cc

Σ

OTP

CONTROL

LOGIC

Driver

+

SW

Q1

-

RAMP

Generator

EN

4

Enable

1.2MHz

Oscillator

2

GND

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AP5726

WHITE LED STEP-UP CONVERTER

Absolute Maximum Ratings

Symbol Parameter Rating Unit

VIN VIN Pin Voltage -0.3~7 V

VSW SW Voltage -0.3~34 V

V

OVP Pin Voltage -0.3~35 V

OVP

VFB Feedback Pin Voltage -0.3~7 V EN EN -0.3~7 V

T

Maximum Junction Temperature 150

J(MAX)

T

Lead Temperature 300

LEAD

T

Storage Temperature Range -65 to +150

ST

Caution: Operation above the absolute maximum ratings can cause device failure. These values, therefore, must not be exceeded under

any condition. Operation at the absolute maximum rating for extended periods, may reduce device reliability.

Recommended Operating Conditions

o

C

o

C

o

C

Symbol Parameter Min Max Unit

VIN Input Voltage 2.7 5.5 V

TJ Operating Junction Temperature -40 125 TA Operating Ambient Temperature -40 85

o

C

o

C

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AP5726

WHITE LED STEP-UP CONVERTER

Electrical Characteristics (V

Symbol Parameter Conditions Min Typ. Max Unit

System Supply Input

VIN Operating Input Voltage 2.7 - 5.5 V

UVLO Under Voltage Lockout - 2.2 2.4 V

Under Voltage Lockout Hysteresis

IQ Quiescent Current FB=0.41V, No Switching - 500 - μA

ISD Shutdown Current VEN < 0.4V - 0.1 1 μA

Oscillator

F

Operation Frequency 1 1.2 1.4 MHz

OSC

Dmax Maximum Duty Cycle 86 90 - %

Reference Voltage

VFB Feedback Voltage 0.279 0.31 0.341 V

IFB FB Pin Bias Current 10 45 100 nA

MOSFET

Rds(on) On Resistance of MOSFET - 0.95 1.2 Ω

I

Switching Current Limit Normal Operation - 750 - mA

OCP

Control and Protection

EN Voltage High ON 1.5 - - V EN Voltage Low OFF - - 0.4 V

IEN EN Pin Pull Low Current - 4 6 μA

OVP OVP Threshold 26 30 34 V

θ

Notes: 2. Test condition for SOT26, TSOT23-6 and DFN2020C-6: Device mounted on FR-4 substrate, single-layer PC board, 2oz copper,

Thermal Resistance Junction-to-

JA

Ambient Thermal Resistance Junction-to-

JC

Case

with minimum recommended pad layout

= 3.6V, TA = 25°C, unless otherwise specified.)

IN

- 85 - mV

SOT26 (Note 2) 162 DFN2020C-6 (Note 2) 200

SOT26 (Note 2) 36 DFN2020C-6 (Note 2) 30

o

C/W TSOT23-6 (Note 2) 152

o

C/W TSOT23-6 (Note 2) 32

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Typical Performance Characteristics (6 LEDs ; V

= 3.6V ; I

IN

AP5726

WHITE LED STEP-UP CONVERTER

= 25mA)

OUT

VIN vs. Shutdown Current

1

0.8

0.6

0.4

0.2

Shutdown Current(uA)

0

2.533.544.555.5

V

(V)

IN

VIN vs. Frequency

1.25

1.2

1.15

1.1

Frequency(MHz)

1.05

V

vs. Quiescent Current

IN

700

600

500

400

300

200

100

Quiescent Current(uA)

0

2.5 3 3.5 4 4.5 5 5.5

100

95

90

Max Duty(%)

85

V

(V)

IN

VIN vs. Max Duty

1

2.5 3 3.5 4 4.5 5 5.5

V

(V)

IN

VIN vs. F eedb ack V olta g e

0.35

0.33

0.31

0.29

0.27

Feedb ack Voltage(V )

0.25

2.53 3.54 4.5 5 5.5

VIN (V)

80

2.533.544.555.5

(V)

V

IN

I

vs. Fee dback Voltage

0.35

0.33

0.31

0.29

0.27

Feedback V o l tag e(V )

0.25 0 1020304050

OUT

I

OUT

(mA)

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Typical Performance Characteristics (Continued)

AP5726

WHITE LED STEP-UP CONVERTER

VIN vs. O VP Threshold

35

33

31

29

27

OVP Threshold(V)

25

2.5 3 3.5 4 4.5 5 5.5

V

(V)

IN

Temperature vs. OVP Threshold

35

30

25

20

Temperature vs. Shutdown Current

1

0.8

0.6

0.4

0.2

Shutdown Current(uA)

0

-50 -25 0 25 50 75 100 125

Temperature (℃)

Temperature vs. Frequency

1.7

VIN = 4.2V

1.4

1.1

0.8

VIN = 3.6V

OVP Threshold(V)

15

10

-50 -25 0 25 50 75 100 125

Temperature (℃)

Frequency (MHZ)

0.5

0.2

-50 -25 0 25 50 75 100 125

Temperature (℃)

Tempera ture vs. Feedback Voltage

0.35

VIN = 4.2V

0.33

0.31

0.29

Feedback Voltage(V)

0.27

0.25

-50 -25 0 25 50 75 100 125

VIN = 3.6V

Tempera ture (℃)

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