Diodes AL8808 User Manual

A

L8808

COST EFFECTIVE LOW EMI 30V 1A BUCK LED DRIVER

Description

The AL8808 is a step-down DC/DC converter designed to drive LEDs

with a constant current. The device can drive up to 8 LEDs,

depending on the forward voltage of the LEDs, in series from a

voltage source of 6V to 30V. Series connection of the LEDs provides

identical LED currents resulting in uniform brightness and eliminating

the need for ballast resistors. The AL8808 switches at frequency up to

1MHz with controlled rise and fall times to reduce EMI. This allows

the use of small size external components, hence minimizing the PCB

area needed.

Maximum output current of AL8808 is set via an external resistor

connected between the V

by applying either an analog DC voltage or a PWM signal at the

CTRL input pin. An input voltage of 0.4V or lower at CTRL switches

off the output MOSFET simplifying PWM dimming.

NEW PRODUCT

and SET input pins. Dimming is achieved

IN

Applications

• MR16 Lamps

• General Illumination Lamps

Notes: 1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.

2. See http://www.diodes.com for more information about Diodes Incorporated’s definitions of Halogen and Antimony free, "Green" and Lead-Free.

3. Halogen and Antimony free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and <1000ppm antimony compounds.

Pin Assignments

(Top View)

1

SW

GND

CTRL

2

3

54V

TSOT25

Features

• LED Driving Current Up to 1A

• Better Than 5% Accuracy

• High Efficiency Up to 96%

• Fast Controlled Falling Edges 7ns

• Operating Input Voltage from 6V to 30V

• High Switching Frequency Up to 1MHz

• PWM/DC Input for Dimming Control

• Built-In Output Open-Circuit Protection

• Built-In Over-Temperature Protection

• TSOT25: Available in “Green” Molding Compound (No Br, Sb)

 Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)

 Halogen and Antimony Free. “Green” Device (Note 3)

IN

SET

Typical Applications Circuit

AL8808

Document number: DS35648 Rev. 2 - 2

1 of 20

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L8808

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Pin Descr

Pin Number

1

2

3

4

5

Function

ptions

Pin Name

SW

GND

CTRL

SET

VIN

l Block Di

Switch Pin.

GND Pin

Dimming an

• Leave (

• Drive t

• Drive w

I

OUTno

• Drive w

• A PWM

current

Set Nominal

Input Supply section for

gram

onnect inducto

On/Off Control

loating for norm

= 5V, Giv

CTRL

voltage below ith an analog vo

ith an analog vo signal (low leve

to be adjusted

Output Current

Pin. Must be lo ore information.

/freewheeling di

Input.

l operation.

s nominal avera

.4V to turn off o tage (0.5V < V

tage > 2.6V out

l  0.4V and hig

elow the level s

in. Configure t

ally decoupled t

Function

de here, minim

ge output curre

tput current

< 2.5V) to a

C

RL

ut current will b level > 2.6; tra

t by the resisto

e output current

o GND with > 2.

zing track lengt

t I

OUTnom

= 0.1/

just output curr

100% of I

OUTn

sition times les

connected to S

of the device.

µF X7R cerami

at this pin to re

)

S

nt from 20% to

m

than 1µs) allo

ET input pin.

c capacitor – se

uce EMI.

100% of

s the output

applications

Figure 1

.

AL8808 Bloc

Diagram

Absolute

aximum

Ratings

(@

T

A

= +25°C, unl

ss otherwise s

ecified.)

Symbol

ESD HBM

ESD MM

VIN

V

SET

VSW

V

CTRL

ISW

TJ

T

LEAD

T

ST

Caution: Stress

AL8808

Document numbe

s greater than th

functio

al operation of th

affecte

d by exposure to a

Semic

nductor devices

and tr

nsporting these d

: DS35648 Rev. 2

Human Body

Machine Mod

Continuous V

SET pin volta

SW voltage r

CTRL pin inp

Switch curren

Junction Tem

Lead Temper

Storage Tem

odel ESD Prot

l ESD Protectio

pin voltage rel

I

N

e relative to V

lative to GND

t voltage

erature

ture Soldering

erature Range

'Absolute Maxi device at these

bsolute maximum

re ESD sensitive vices.

- 2

Parameter

ction

n

tive to GND

IN

um Ratings' spec

r any other condi

rating conditions f

nd may be dama

ified above, may

ions exceeding th r extended period

ed by exposure t

2 of 20

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ause permanent se indicated in th of time. ESD events. Sui

m

Ratin

2.5

20

-0.3 to

-5 to +

-0.3 to

1.2

15

-55 to

amage to the de

s specification is

able ESD precaut

s

+33

0.3

+33

+6

150

ice. These are s

ot implied. Devic

ions should be ta

Unit

kV

V

A

°C

ess ratings only;

reliability may be

en when handling

January 201

3

d

A

Recommended Operating Conditions (@T

= +25°C, unless otherwise specified.)

A

Symbol Parameter Min Max Unit

VIN

V

CTRLH

V

CTRLDC

V

CTRLL

ISW

fSW

TJ

Note: 4. Subject to ambient temperature, input voltage and switching frequency. See applications section for suggested derating.

Electrical Characteristics (@ T

Symbol Parameter Conditions Min Typ Max Unit

V

NEW PRODUCT

INSU

V

INSH

IQ

IS

VTH

V

TH-H

I

SET

V

CTRL

R

CTRL

V

REF

R

DS(on)

I

SW_Lkg

tR

tF

T

OTP

T

OTP-Hyst

θJA

θJL

θJT

Notes: 5. Device mounted on FR-4 PCB (25mm x 25mm 1oz copper, minimum recommended pad layout on top layer and thermal vias to maximum area

bottom layer ground plane. For better thermal performance, larger copper pad for heat-sink is needed. …Refer to Figure 42 for the device derating curve.

AL8808

Document number: DS35648 Rev. 2 - 2

Operating Input Voltage Relative to GND 6.0 30 V

Voltage High for PWM Dimming Relative to GND 2.6 5.5 V

Voltage Range for 20% to 100% DC Dimming Relative to GND 0.5 2.5 V

Voltage Low for PWM Dimming Relative to GND 0 0.4 V

Continuous Switch Current (Note 4) 1 A

Maximum Switching Frequency 1 MHz

Junction Temperature Range -40 +125 °C

= +25°C, VIN = 12V, CTRL pin floating; unless otherwise specified.)

A

Internal Regulator Start Up Voltage

Internal Regulator Hysteresis Threshold

Quiescent Current

Input Supply Current

VIN rising

VIN falling

VIN = 30V, output not switching

fSW = 250kHz

5.6 V

200 mV

350 µA

450 µA

Set Current Threshold Voltage 95 100 105 mV

Set Threshold Hysteresis ±20 mV

SET Pin Input Current

V

= V

IN

-0.1

SET

16 µA

Open Circuit CTRL Pin Voltage 5 V

CTRL Pin Input Resistance Referred to internal 5V regulator. 50 k

Internal Reference Voltage 2.5 V

On Resistance of SW MOSFET

Switch Leakage Current

SW Rise Time

SW Fall Time 5 ns

Over-Temperature Shutdown

Over-Temperature Hysteresis 10 °C

ISW = 0.35A

VIN = 30V, V

V

= 100 ±20mV, fSW = 250kHz

SENSE

CTRL

= 0.4V, V

SENSE

= 0V

VSW = 0.1V to 12V to 0.1V, CL = 15pF

0.35 

0.5 µA

7 ns

145 °C

Thermal Resistance Junction-to-Ambient TSOT25 (Note 5) 209

Thermal Resistance Junction-to-Lead TSOT25 (Note 5) 57

Thermal Resistance Junction-to-Top TSOT25 (Note 5) 13

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L8808

°C/W

January 2013

A

P

U

T

C

URRENT

F

REQ

UENCY

H

CUR

RENT

CTRL PIN CUR

REN

T

C

U

R

T ER

ROR

C

R

UTY CYC

Typical Performance Characteristics (@ T

NEW PRODUCT

400

350

300

(µA)

250

200

150

IN

100

50

0

0 3 6 9 12 15 18 21 24 27 30

INPUT VOLTAGE (V)

Figure 2. Supply Current vs. Input Voltage

1.2

R

T = +25°C

A

V= 12V

IN

1.0

L = 68µH 1 LED

0.8

(A)

SET

R

0.6

0.4

LED

0.2

V = 0V

CTRL

V = V

SET IN

T = +25°C

A

= 100m

= 150m

SET

R

= 300m

SET

L8808

= +25°C, unless otherwise stated.)

A

900

800

700

z)

600

(k

500

400

300

200

100

0

20

Ω

0

-20

(µA)

Ω

-40

-60

-80

Ω

-100

L = 33µH

L = 100µH

T = +25°C

A

V = 12V

IN

R = 150m

SET

1 LED

L = 68µH

Ω

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 V

(V)

= 150m

CTRL

Ω

Figure 3. Switching Frequency vs. V

T = +25°C, V = 12V

AIN

L = 68µH, R 1 LED

SET

0.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 V

(V)

Figure 4. LED Current vs. V

CTRL

6

T = +25°C, V = 12V

AIN

L = 68µH, R 1 LED, f = 500Hz

5

PWM

SET

= 150m

Ω

(%)

4

3

EN

2

LED

1

0

020406080100

PWM DUTY CYCLE (%)

Figure 6. I vs. PWM Duty Cycle

LED

0.9

LED

0.6

U

ENT (A)

0.3

0.0

-120

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 V

(V)

Figure 5. I vs. V

CTRL

CTRL CTRL

100

90

80

70

60

LE (%)

50

40

D

30

20

T = +25°C, R = 150m

A SET

10

L = 33µH, L = 68µH, L = 100µH

0

6 9 12 15 18 21 24 27 30

INPUT VOLTAGE V

Ω

(V)

CTRL

Figure 7. Duty Cycle vs. Input Voltage

AL8808

Document number: DS35648 Rev. 2 - 2

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5

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5

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5

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S

2

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T

S

w

t

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u

r

M

OSFET R

=

V

°

p

r

8

O

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A

L8808

NEW PRODUCT

Typical P

Ω

(m )

DS(ON)

SW M

0.5

0.4

Ω

0.3

rformanc

6

0

V = Open

CTRL

V = V = 1

SET IN

5

0

-40 -25 -10 5

Figure 8.

V = 12V

IN

V = V

SET IN

T = +25°C

A

CTRL = Floating

Charact

V

20 35

AMBI

ENT TEMPERA SW R vs

50 6

DS(ON)

ristics

(con

80 95 110 1

URE (°C)

. Temperature

.) (@ TA = +25°

25

, unless other

400

350

300

Ω

(m )

250

DS(ON)

200

150

100

SW

V

CTRL

V =

50

SET

T = 25

A

0

69

ise stated.)

Open

IN

C

12 15 1

Fig

ure 9. SW R

DS(

V

IN

21 24

(V)

vs. Input Volt

N)

27 30

ge

0.3

DS(ON)

0.2

0.1

SW MOSFET R ( )

0.1

0.0

0.0 0200

S

Figure 10.

400 600

ITCH CURREN

SW R vs.

DS(ON)

800 1

(mA) witch Current

000

Fig

re 11. SW Out

ut Fall Time

Figure 12.

AL8808

Document numbe

: DS35648 Rev. 2

teady State W

- 2

veforms

5 of 20

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m

Figu

e 13. SW Outp

ut Rise Time

January 201

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A

C

Y

C

URREN

T

TCHING F

REQ

UENC

Y

H

CUR

RENT

U

T

Y CYC

CUR

R

T

L8808

Typical Performance Characteristics (L = 68µH, T

NEW PRODUCT

100

95

3 LEDs

2 LEDs

5 LEDs

4 LEDs

90

(%)

1 LED

85

IEN

80

EFFI

T = 25°C

A

L= 68µH

75

R = 150m

SET

Ω

70

6 9 12 15 18 21 24 27 30

INPUT VOLTAGE (V)

Figure 14. Efficiency vs. Input Voltage

450

400

z)

350

(k

300

250

7 LEDs

= +25°C, unless otherwise stated.)

A

0.36

0.35

0.34

(A)

2 LEDs

0.33

0.32

LED

0.31

0.30 6 9 12 15 18 21 24 27 30

Figure 15. 330mA LED Current vs. Input Voltage

0.74

0.72

2 LEDs

0.70

(A)

0.68

3 LEDs

T = 25°C

A

L= 68µH R = 300m

SET

3 LEDs

1 LED

4 LEDs

Ω

5 LEDs

INPUT VOLTAGE (V)

5 LEDs

4 LEDs

7 LEDs

200

150

1 LED

LED

0.66

0.64

1 LED

100

SWI

50

5 LEDs

3 LEDs

4 LEDs

2 LEDs

0

6 9 12 15 18 21 24 27 30

7 LEDs

INPUT VOLTAGE (V)

Figure 16. Switching Frequency vs. Input Voltage

100

90

2 LEDs

4 LEDs

3 LEDs

5 LEDs

80

70

1 LED

60

LE (%)

50

7 LEDs

0.62

T = 25°C, V

A

L= 68µH, R = 150m

0.60 6 9 12 15 18 21 24 27 30

SET

IN

= 12V

Ω

INPUT VOLTAGE (V)

Figure 17. 670mA LED Current vs. Input Voltage

1.10

7 LEDs

1.05

2 LEDs

3 LEDs

4 LEDs

5 LEDs

(A)

EN

1.00

1 LED

40

30

D

20

T = 25°C

A

L= 68µH

10

R = 150m

SET

0

6 9 12 15 18 21 24 27 30

Ω

INPUT VOLTAGE (V)

Figure 18. Duty Cycle vs. Input Voltage

LED

0.95

T = 25°C

A

L= 68µH R = 100m

SET

0.90 6 9 12 15 18 21 24 27 30

Ω

INPUT VOLTAGE (V)

Figure 19. 1A LED Current vs. Input Voltage

AL8808

Document number: DS35648 Rev. 2 - 2

6 of 20

www.diodes.com

January 2013