Diodes AP5725 User Manual

AP5725

WHITE LED STEP-UP CONVERTER

Description

The AP5725 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, AP5725 also supports a single feedback of parallel connected multiple strings of equal number of LEDs.

The AP5725 switches at 1.2MHz that allows the use of tiny external components. A low 0.25V 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 held 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

AP5725

Document number: DS31844 Rev. 3 - 2

L1

22uH

C

IN

D1

1uF

V

AP5725

EN

IN

SW

OVP

FB

GND

Figure 1. Typical Application Circuit

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R

12

SET

2~6 LEDs

C

OUT

1uF

July 2010

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 0.25V. Connect cathode of lowest LED and a sense resister here. Calculate resistor value according to the formula: R

= 0.25V / 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

AP5725

1

Comparator

-

A2

+

Rc

A1

-

+

FB

3

V

6

IN

REF

0.25V

Cc

Σ

OTP

CONTROL

LOGIC

Driver

+

SW

Q1

-

RAMP

Generator

EN

4

Enable

1.2MHz

Oscillator

2

GND

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AP5725

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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AP5725

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 Hysteretic - 85 - mV

IQ Quiescent Current FB=0.35V, 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 0.225 0.25 0.275 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

SOT26 (Note 2) 162 DFN2020C-6 (Note2) 200

SOT26 (Note 2) 36

DFN2020C-6 (Note 2) 30

o

C/WTSOT23-6 (Note 2) 152

o

C/WTSOT23-6 (Note 2) 32

AP5725

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Typical Performance Characteristics (6 LEDs ; V

= 3.6V ; I

IN

AP5725

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. Feed b ack V o lta g e

0.3

0.28

0.26

0.24

0.22

Feedback Vol tag e(V )

0.2

2.5 3 3.5 4 4.5 5 5.5

V

(V)

IN

80

2.533.544.555.5

I

vs. Feedback Voltage

OUT

0.3

0.28

0.26

0.24

0.22

Feedback V oltage(V)

0.2 0 1020304050

I

OUT

V

IN

(mA)

(V)

AP5725

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Typical Performance Characteristics (Continued)

AP5725

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 (℃)

Tem perature vs. Fee dback Voltage

0.28

0.27

V

= 4.2V

IN

0.26

V

0.25

0.24

Feedback V o l tag e(V )

0.23

-50 -25 0 25 50 75 100 125

Temperature(℃)

= 3.6V

IN

AP5725

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Typical Performance Characteristics (Continued)

I

vs. Efficiency

OUT

90

AP5725

WHITE LED STEP-UP CONVERTER

I

vs. Efficiency

OUT

90

85

80

75

70

Efficiency(%)

65

4 LEDs ; L = 22uH

60

0 5 10 15 20 25 30

100

90

80

70

60

Efficiency(%)

50

3 LEDs

V

= 4.2V

VIN = 3.6V

(mA)

I

OUT

V

vs. Efficiency

IN

4 LEDs

6 LEDs

85

80

75

70

Efficiency(%)

65

6 LEDs ; L = 22uH

60

0 5 10 15 20 25 30

VIN = 4.2V

VIN = 3.6V

(mA)

I

OUT

40

2.5 3 3.5 4 4.5 5

AP5725

Document number: DS31844 Rev. 3 - 2

VIN (V)

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Typical Performance Characteristics (Continued)

Ripple

V

= 3.6V; 4 LEDs ; IOUT = 30mA

V

IN

OUT

AP5725

WHITE LED STEP-UP CONVERTER

V

Ripple

= 3.6V; 6 LEDs ; IOUT = 30mA

V

IN

OUT

SW SW

VOUT

V

OUT

POWER ON

= 3.6V; 6 LEDs ; IOUT = 30mA

V

IN

VEN

OUT

V

Irushi

VIN = 3.6V; 6 LEDs ; IOUT = 30mA

POWER OFF

VEN

OUT

V

Irushin

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AP5725

WHITE LED STEP-UP CONVERTER

Applications Information

Inductor Selection

A 10μH~22μH inductor is recommended for most AP5725 applications. For high efficiency the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance). The inductor saturation current rating should also exceed the peak input current, especially for high load current applications (like 3S8P).

Capacitor Selection The small size of ceramic capacitors are ideal for AP5725 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1μF input capacitor and a 1μF output capacitor are sufficient for most AP5725 applications. For high output current applications like 3S8P, larger output capacitor of 2.2uF ~ 4.7uF is recommended to minimize output ripple.

Diode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AP5725 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode, while the diode capacitance (C

or CD) represents the switching losses. For diode selection, both forward voltage drop

T

and diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.2MHz switching frequency of the AP5725. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance. Larger Schottky diode capacitance can cause significant switching losses at the 1.2MHz switching frequency of the AP5725. A Schottky diode rated at 100mA to 200mA is sufficient for most AP5725 applications.

LED Current Control The LED current is controlled by the feedback resistor (R LED current is 0.25V/ R recommended). The formula and table for R R

SET

= 0.25V/I

(See Table 1)

LED

. In order to have accurate LED current, precision resistors are preferred (1% is

SET

selection are shown below.

SET

in Figure 1). The feedback reference is 0.25V. The

SET

Table 1. R

I

LED

Resistor Value Selection

SET

(mA) R

SET

(Ω)

5 50 10 25 15 16.6 20 12.5 30 8.3

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AP5725

WHITE LED STEP-UP CONVERTER

Applications Information (Continued)

Open-Circuit Protection

In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail, the feedback voltage will be zero. The AP5725 will then switch at a high duty cycle resulting in a high output voltage, which may cause the SW and OVP pin voltage to exceed the voltage rating of these pins. The OVP pin monitors the output voltage. If the output voltage reaches the over voltage protection threshold at the OVP pin (Figure 2), the over voltage protection is activated and SW pin stops switching.

L1

V

IN

C

IN

22uH

1uF

D1

C

OUT

1uF

V

IN

SW

x

AP5725

EN

GND

Figure 2. LED Driver with Open-Circuit Protection

Dimming Control

There are four different types of dimming control circuits:

1. Using a PWM Signal to EN Pin

With the PWM signal applied to the EN pin, the AP5725 is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM signal. A 0% duty cycle will turn off the AP5725 and corresponds to zero LED current. A 100% duty cycle corresponds to full current. The typical frequency range of the PWM signal is below 2kHz.

OVP

FB

x

RSET

12

AP5725

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AP5725

WHITE LED STEP-UP CONVERTER

Applications Information (Continued)

2. Using a DC Voltage

For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown in Figure 3. As the DC voltage increases, the voltage drop on R2 increases and the voltage drop on R selection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias current. For V dimming control of LED current from 0mA to 20mA.

range from 0V to 2V, the selection of resistors in Figure 3 gives

DC

AP5725

FB

decreases. Thus, the LED current decreases. The

SET

R3

100k

V

DC

R2

5k

RSET

12

Figure 3. Dimming Control Using a DC Voltage

3. Using a Filtered PWM Signal

The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC voltage source in dimming control.

4. Using a Logic Signal

For applications that need to adjust the LED current in discrete steps, a logic signal can be used as shown in Figure 4. R increases when the NMOS is turned on.

sets the minimum LED current (when the NMOS is off). R

SET

sets how much the LED current

SET

AP5725

FB

AP5725

Document number: DS31844 Rev. 3 - 2

RINC

Logic

RSET

Signal

Figure 4. Dimming Control Using a Logic Signal

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Applications Information (Continued)

VOUT

C1 1uF

D2

LED

D3

LED

D4

LED

D5

LED

D6

LED

D7

LED

D1 B0540WS

R1 12ohm

1 2 3

AP5725

WHITE LED STEP-UP CONVERTER

VIN

L1 22uH

U1

SW GND FB

AP5725

Vin

OVP

EN

6 5 4

C2 1uF

ON OFF

Table 2. Suggested Inductors

Vendor

Inductors

(uH)

Current Rating

(A)

Type

Dimensions

(mm)

Series

Wurth Electronics 22 0.51A SMD 3.8X 3.8 X 1.6 744031220

GOTREND 22 0.56A SMD 3.8 X 3.8 X 1.05 GLP3810PH220N

TAIYO YUDRN 22 0.51A SMD 4.0 X 4.0 X 1.25 NR4012

Table 3. Suggested Capacitors for C

and C

IN

OUT

Vendor Capacitance Type Series

TAIYO YUDEN 1uF SMD TMK212 B7105MG-T

Table 4. Suggested Diodes

Vendor Rating Type Series

ZETEX 40V/0.5A SOD323 ZLLS400 DIODES 40V/0.5A SOD323 B0540WS DIODES 40V/0.25A SOD523 SDM20U40

Table 5. Suggested Resistor

Vendor Type Series

YAGEO SMD FR-SK

Table 6. Suggested W-LED

Vendor Type Series

LITEON SMD LTW-C1911UC5

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Ordering Information

AP 5725 XXX

AP5725

WHITE LED STEP-UP CONVERTER

G - 7

Package

W : SOT26

WU : TSOT23-6

FDC : DFN2020C-6

Green

G : Green

Packing

7 : Tape & Reel

Device

AP5725WG-7 W SOT26 3000/Tape & Reel -7 AP5725WUG-7 WU TSOT23-6 3000/Tape & Reel -7 AP5725FDCG-7 FDC DFN2020C-6 3000/Tape & Reel -7

Notes: 3. 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.

Package

Code

Packaging

(Note 3)

Quantity Part Number Suffix

7” Tape and Reel

Marking Information

(1) SOT26 and TSOT23-6

( Top View )

6

5

7

4

XX : Identification Code

Y

XX Y

WX

: Year 0~9

W : Week : A~Z : 1~26 week;

a~z : 27~52 week; z represents

1 2 3

52 and 53 week

X

: A~Z : Green

Part Number Package Identification Code

AP5725WG-7 SOT26 FC

AP5725WUG-7 TSOT23-6 GC

(2) DFN2020C-6

AP5725FDCG-7 DFN2020C-6 GC

AP5725

Document number: DS31844 Rev. 3 - 2

( Top View )

: Identification Code

XX

Y W X

Part Number Package Identification Code

www.diodes.com

Y : Year : 0~9

W

: Week : A~Z : 1~26 w eek;

a~z : 27~52 week; z represents

52 and 53 week

X

: A~Z : Green

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Package Outline Dimensions (All Dimensions in mm)

(1) Package Type: SOT26

AP5725

WHITE LED STEP-UP CONVERTER

(2) Package Type: TSOT23-6

AP5725

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Package Outline Dimensions (Continued)

(3) Package Type: DFN2020C-6

AP5725

WHITE LED STEP-UP CONVERTER

Marking

1.95/2.075

1.55/1.75

0.15max.

A

0.25/0.35

0.43mon.

(Active area depth)

Seating plane

C

0.10

M C A B

0.37

Top View

0.9

0.45

0.65

1.59

Land Pattern Recommendation

(Unit:mm)

2x-

0.10 C

0.08 C

Pin#1 ID

0.25 B

0.57/0.63

0/0.05

B

R

0

0.86/1.06

1.95/2.075

0.1

R

0.65nom.

A

0.25

2x

.

1

5

Bottom View

AP5725

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Taping Orientation

For DFN2020C-6

AP5725

WHITE LED STEP-UP CONVERTER

Notes: 4. The taping orientation of the other package type can be found on our website at http://www.diodes.com/datasheets/ap02007.pdf.

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AP5725

WHITE LED STEP-UP CONVERTER

IMPORTANT NOTICE

DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 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 arising out of the application or use of this document or any product described herein; neither does Diodes In corporated convey any license under its patent or trademark rights, nor the rights of others. Any Customer or user of this documen t 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 Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel. Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.

Products described herein may be covered by one or more United States, international or foreign p atents pending. Product names and markings noted herein may also be covered by one or more United States, international or foreign trademarks.

LIFE SUPPORT

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 Executive Officer of Diodes Incorporated. As used herein:

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 component is any component in a life support device or system whose failure to perform can be reasonably expected

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

Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support dev ices 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, notwithstanding any devices- or systems-related information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems.

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AP5725

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