Diodes AL8805 User Manual

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Description

The AL8805 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 36V. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The AL8805 switches at frequency up to 1MHz. This allows the use of small size external components, hence minimizing the PCB area needed.

Maximum output current of AL8805 is set via an external resistor connected between the V by applying either a 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.

and SET input pins. Dimming is achieved

IN

HIGH EFFICIENCY 36V 1A BUCK LED DRIVER

Pin Assignments

SW

GND

CTRL

(Top View)

1

2

3

SOT25

5V

IN

4SET

L8805

Features

• LED Driving Current up to 1A

• Better than 5% Accuracy

• High Efficiency up to 98%

• Operating Input Voltage from 6V to 36V

• High Switching Frequency up to 1MHz

• PWM/DC Input for Dimming Control

• Built-In Output Open-Circuit Protection

• SOT25: Available in “Green” Molding Compound (No Br,Sb) with lead Free Finish/ RoHS Compliant

 Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)  Halogen and Antimony Free. “Green” Device (Note 3)

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.

Applications

• MR16 Lamps

• General Illumination Lamps

Typical Applications Circuit

AL8805

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L8805

Pin Descriptions

Pin Number Pin Name Function

1 SW Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI. 2 GND GND Pin

Dimming and On/Off Control Input.

• Leave floating for normal operation. = V

3 CTRL

• Drive to voltage below 0.4V to turn off output current

• Drive with DC voltage (0.5V < V

(V

CTRL

= 2.5V giving nominal average output current I

REF

< 2.5V) to adjust output current from 20% to 100% of I

CTRL

OUTnom

= 0.1/RS)

OUTnom

• A PWM signal (low level ≤ 0.4V and high level > 2.6; transition times less than 1us) allows the output

current to be adjusted below the level set by the resistor connected to SET input pin.

4 SET Set Nominal Output Current Pin. Configure the output current of the device.

5 VIN

Input Supply Pin. Must be locally decoupled to GND with > section for more information.

2.2µF X7R ceramic capacitor – see applications

Absolute Maximum Ratings (@T

= +25°C, unless otherwise specified.)

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Symbol Parameter Ratings Unit

ESD HBM Human Body Model ESD Protection 2.5 kV

ESD MM Machine Model ESD Protection 200 V

VIN Continuous VIN Pin Voltage Relative to GND -0.3 to 40 V

V

SET Pin Voltage Relative to VIN Pin -5 to +0.3 V

SET

VSW SW Voltage Relative to GND -0.3 to 40 V

V

CTRL Pin Input Voltage -0.3 to 6 V

CTRL

I

DC or RMS Switch current 1.25 A

SW-DC

I

Peak Switch Current (<10%) 2.5 A

SW-PK

TJ Junction Temperature 150 °C

T

Lead Temperature Soldering 300 °C

LEAD

T

Storage Temperature Range -65 to +150 °C

ST

Caution: Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only;

Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and

functional operation of the device at these or any other conditions exceeding those indicated in this specification is not implied. Device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time.

transporting these devices

Recommended Operating Conditions (@T

= +25°C, unless otherwise specified.)

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Symbol Parameter Min Max Unit

VIN Operating Input Voltage relative to GND 6.0 36 V

V

Voltage High for PWM Dimming Relative to GND 2.6 5.5 V

CTRLH

V

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

CTRLDC

V

Voltage Low for PWM Dimming Relative to GND 0 0.4 V

CTRLL

ISW Continuous Switch Current — 1 A

TJ Junction Temperature Range -40 125 °C

AL8805

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L8805

Electrical Characteristics (V

= 12, @TA = +25°C, unless otherwise specified.)

IN

Symbol Parameter Conditions Min Typ Max Unit

V

Internal Regulator Start Up Threshold VIN rising 5.9 V

INSU

V

Internal Regulator Hysteresis Threshold VIN falling 100 300 mV

INSH

IQ Quiescent Current Output not switching (Note 4) 350 µA IS Input Supply Current CTRL pin floating f = 250kHz 1.8 5 mA

VTH Set Current Threshold Voltage 95 100 105 mV

V

Set Threshold Hysteresis ±20 mV

TH-H

I

SET Pin Input Current V

SET

R

CTRL Pin Input Resistance Referred to internal reference 50 kΩ

CTRL

V

Internal Reference Voltage 2.5 V

REF

R

On Resistance of SW MOSFET ISW = 1A 0.25 0.4 Ω

DS(on)

I

SW_Leakage

Notes: 4. AL8805 does not have a low power standby mode but current consumption is reduced when output switch is inhibited: V tested with V

5. Refer to figure 34 for the device derating curve.

6. Test condition for SOT25: Device mounted on FR-4 PCB (25mm x 25mm 1oz copper, minimum recommended pad layout on top layer and thermal vias to bottom layer ground plane. For better thermal performance, larger copper pad for heat-sink is needed.

7

Switch Leakage Current VIN = 30V 0.5 μA

f

Switching Frequency 1 MHz

OSC

θ

Ψ

Thermal Resistance Junction-to-

JA

Ambient (Note 5) Thermal Resistance Junction-to-Lead

JB

(Note 7)

≤ 2.5V

CTRL

. As SOT25 doesn’t have an exposed tab or exposed pad the majority of heat flow is though pin 2 down to ground.

AL8805

Document number: DS35030 Rev. 4 - 2

= VIN-0.1 16 22 µA

SET

SOT25 (Note 6) 250

SOT25 50

= 0V. Parameter is

SENSE

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F

REQUENC

Y

A

L8805

Typical Performance Characteristics (@T

400

V = 0V

CRTL

V = V

350

SET IN

T = 25°C

A

300

250

200

IN

I (µA)

150

100

50

0

06

12

18

V (V)

IN

24

30 36

Figure 1 Supply Current (not switching) vs. Input Voltage

1

0.9

0.8

V = 12V

IN

1 LED L = 68µH T = 25°C

A

R = 100m

SET

Ω

0.7

0.6

0.5

LED

I (A)

0.4

0.3

R = 150m

SET

R = 300m

SET

Ω

0.2

0.1 0

012345

Figure 3 LED Current vs. V

V (V)

CTRL

3

= +25°C, unless otherwise specified.)

A

900

L = 33µH

800 700 600

(kHz)

500

L = 68µH

400 300 200

L = 100µH

100

0

012345

Figure 2 Switching Frequency vs . V

80

V = V = 12V

SET IN

T = 25°C

A

60

40

)

20

CTRL

0

I (µ

-20

-40

-60

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

2.52

V(V)

CTRL

V (V)

Figure 4 I vs. V

CTRL

CTRL CTRL

V = 12V

IN

1 LED R = 150m

SET

T = 25°C

A

CTRL

Ω

V = Open

CTRL

2.5

V = V = 12V

SET IN

2.51

2

1.5

CTRL

V (V)

2.50

CTRL

V (V)

1

2.49

V = Open

CTRL

0.5

0

0 3 6 9 12 18 21 24 27 30 36

Figure 5. V vs. Input Voltage

15 33

V (V)

IN

CTRL

V = V

SET IN

T = 25°C

A

2.48

-40 -15 10 35 60 85 110 AMBIENT TEMPERATURE (°C)

Figu r e 6 V vs. Temper ature

CTRL

(CTRL Pin Open Circuit)

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CUR

RENT

R

ROR

R

UTY

C

Y

C

Typical Performance Characteristics (cont.) (@T

5.0

4.5

4.0

(%)

3.5

3.0

E

2.5

2.0

1.5

LED

1.0

0.5

0.0 0% 20% 40% 60% 80% 100%

PWM DUTY CYCLE

Fig u re 7 I vs. PWM Duty Cyc le

LED

400

350

300

Ω

250

DS(ON)

R(m)

200

150

100

-40 -15 10 35 60 85 110 AMBIENT TEMPERATURE (°C)

Figure 9 SW R vs. Temperature

R = 150m , L =68µH, V = 12V, 1LED Load, T =25 C

SET IN A

1

Duty Cycle = 5%

Ω°

0.9

DS(ON)

I

LED

0.8

0.7

V

SW

0.6

0.5

0.4

LED CURRENT (A)

0.3

0.2

0.1 0

050100150200

V

CTRL

Time (µs)

Figure 11 PWM Dimming

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1 0

20 18

16 14 12 10 8

6 4

2 0

LED CURRENT (A)

SWITCH an d CTRL VO LTAGE (V)

= +25°C, unless otherwise specified.)

A

300

240

180

Ω

(m )

120

DS(ON)

60

0

6

12 18 24 30 36

Figure 8 SW R vs. Input Voltage

130 125

120 115

V

SENSE

110 105

SENSE

100

V(mV)

95 90 85

80

TIME (µs)

Figure 10 SW Output Switching Characteristics

LE

D

6 912151821242730

INPUT VOLTAGE (V)

Figure 12 Duty Cycle vs. Input Voltage

V (V)

IN

DS(ON)

V = Open

CTRL

V = V

SET IN

T = 25C

A

R = 150m

SET

L = 68µH V = 12V

IN

1 LED Load

V

SW

L = 33µH R = 150m

S

T = 25°C

A

2 LED

°

Ω

33 36

L8805

18 16

14 12

10

8

V

6 4

2 0

-2

Ω

SW

AL8805

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