Diodes AL8807A User Manual

A

L8807A

HIGH EFFICIENCY LOW EMI WIDE ANALOG

DIMMING RANGE 36V 1A/1.3A BUCK LED DRIVER

Description

The AL8807A is a step-down DC/DC converter designed to drive LEDs with a constant current. The device can drive up to 9 white high brightness LEDs in series from a voltage source of 6V to 36V.

The AL8807A has an extended CTRL pin voltage range; increasing its analog dimming range to greater than 10:1. The improved analog dimming range makes it suitable for a variety of lighting applications requiring wide analog dimming ranges.

The AL8807A 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 AL8807A is set via an external resistor connected between the V

Over Temperature Protection is incorporated so that should a fault occur the device will automatically shut-down and only restart when its junction temperature has cooled down,

and SET input pins.

IN

Features

 LED Driving Current up to 1A/1.3A  Better than 5% Accuracy  High Efficiency Up to 96%  Optimally Controlled Switching Speeds  Operating Input Voltage from 6V to 36V  Wide Analog Input Range for Dimming Control (>10:1)  Built-in Protection Features:

 Open-Circuit LED protection  LED Chain Short Circuited  Over-Temperature Protection

 MSOP-8EP and 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.

Pin Assignments

(Top View)

SOT25

(Top View)

SET

1

GND

2

GND

3

CTRL

4

MSOP-8EP

Applications

 General Illumination Lamps  12V Powered LED Lamps  Wide Analog Dimming Range LED Lamps

V

8

IN

N/C

7

SW

6

SW

5

Typical Applications Circuit

AL8807A

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L8807A

Pin Descriptions

Pin Name

SW 1 5, 6 Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI.

GND 2 2, 3 GND Pin

CTRL 3 4

SET 4 1 Set Nominal Output Current Pin. Configure the output current of the device.

VIN

EP — EP

N/C — 7 No connection – may be connected to GND.

SOT25 MSOP-8EP

Functional Block Diagram

Pin Number

LED current Analog Dimming Control Input. – No PWM dimming function. Connected to internal 2.5V V LED current is achieved - giving nominal average output current I For Analog dimming drive with analog voltage < 2.5V

(0.25V < V lower than this level but at reduced accuracy. Some devices will not totally turn off the LED current.

Soft-start can be implemented by connecting a capacitor to CTRL pin. The amount of soft-start is dependent on ramp-up of input supply voltage and capacitor on CTRL pin. See apps section.

5 8

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

Exposed pad/TAB. It should be connected to GND and thermal mass for enhanced thermal impedance. It should not be used as electrical ground conduction path.

Function

via 50k resistor. So if left open circuit V

REF

< 2.5V adjusts output current from 10% to 100% of I

CTRL

OUTnom

2.2µF X7R ceramic capacitor – see

= V

CTRL

= 0.1/RS

. Device will dim the LED current

= 2.5V and 100%

REF

AL8807A

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L8807A

Absolute Maximum Ratings (@T

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

VSW

V

CTRL

I

SW-RMS

I

SW-PK

TJ

T

LEAD

T

ST

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

SW Voltage Relative to GND -0.3 to +40 V CTRL Pin Input Voltage -0.3 to +6.0 V

DC or RMS Switch Current Peak Switch Current (< 10% duty cycle) 2.5 A

Junction Temperature 150 °C Lead Temperature Soldering 300 °C Storage Temperature Range -65 to +150 °C

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.

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

and transporting these devices.

Recommended Operating Conditions (@T

Symbol Parameter Min Max Unit

VIN

V

CTRL

fSW ISW

TJ

Notes: 4. AL8807A analog dimming range extends below 10% but at reduced LED current accuracies and may not turn completely off. Switching frequencies will also be increased.

5. Maximum switch current is dependent on power dissipation and junction temperature.

Operating Input Voltage 6.0 36 V CTRL Pin Input Voltage Range for 10% to 100% ANALOG Dimming (Note 4) 0.25 2.50 V Maximum Switching Frequency at 100% dimming 0.7 MHz

Continuous Switch Current (Note 5) Junction Temperature Range -40 +125 °C

= +25°C, unless otherwise specified.)

A

SOT25 1.25 MSOP-8EP 1.5

= +25°C, unless otherwise specified.)

A

SOT25 1 MSOP-8EP 1.3

-0.3 to +40 V

A

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Electrical Characteristics (@T

Symbol Parameter Conditions Min Typ Max Unit

V

INSU

V

INSH

IQ

VTH

V

TH-H

V

TH-10%

I

SET

R

CTRL

V

REF

R

DS(on)

tR

I

SW_Leakage

T

OTP

T

OTP-Hyst







Notes: 6. AL8807A does not have a low power standby mode but current consumption is reduced when output is not being switched.

7. Refer to Figure 40 for the device derating curve.

8. 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.

9. Test condition for MSOP-8EP: Device mounted on FR-4 PCB (51mm x 51mm 2oz copper, minimum recommended pad layout on top layer and

thermal vias to bottom layer with maximum area ground plane. For better thermal performance, larger copper pad for heat-sink is needed.

10. Dominant conduction path via Gnd pin (pin 2).

11. Dominant conduction path via exposed pad.

AL8807A

Document number: DS35990 Rev. 2 - 2

Internal Regulator Start Up Threshold Internal Regulator Hysteresis Threshold Quiescent Current

IS

Input Supply Current f = 250kHz 1.8 5 mA Set Current Threshold Voltage Set Threshold Hysteresis ±20 % 10% Set Current Threshold Voltage SET Pin Input Current CTRL Pin Input Resistance Referred to internal reference 50 k Internal Reference Voltage 2.5 V

On Resistance of SW MOSFET

SW Rise Time

tF

SW Fall Time 20 ns Switch Leakage Current Over-Temperature Shutdown Over-Temperature Hysteresis 25 C

Thermal Resistance Junction-to-Ambient

JA

(Note 7) Thermal Resistance Junction-to-Lead

JL

(Note 10) Thermal Resistance Junction-to-case

JC

(Note 11)

= +25°C, unless otherwise specified.)

A

VIN rising VIN falling

CTRL pin

Output not switching (Note 6) 350 µA

floating

CTRL pin floating

V

= 0.25V

CTRL

V

= V

SET

ISW = 0.3A

V

SENSE

V

SW

-0.1

IN

SOT25 0.25 0.40 MSOP-8EP 0.18 0.35

= 100 ±20mV, fSW = 250kHz

= 0.1V ~ 12V ~ 0.1V, CL = 15pF

VIN = 36V

SOT25 (Note 8) 250 MSOP-8EP (Note 9) 69

SOT25 (Note 8) 50

MSOP-8EP (Note 9) 4.3

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5.9 V

100 300 mV

95 100 105 mV

4 10 15 mV

16 22 µA



12 ns

0.5 A 150 C

°C/W

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R

Typical Performance Characteristics

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

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

80

V

= VIN = 12V

60

SET

= 25°C

T

A

40

20

(µA)

0

CTRL

I

-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

Figure 2 I

V

CTRL

(V)

vs. V

CTRL

L8807A



(m )

300

240

180

DS(ON)

120

Figure 3 V

vs Input Voltage

CTRL

(CTRL pin open circuit)

MSOP-8EP

SOT25

2.52 V

= Open

CTRL

= VIN = 12V

V

SET

2.51

(V)

2.50

CTRL

V

2.49

2.48

-40 -15 10 35 60 85 110 Ambient Temperature (°C)

400

Figure 4 V

V = Open

CTRL

V = V = 12V

SET IN

vs. Temperature

CTRL

350

300



(m )

250

DS(ON)

200

SOT25

MSOP-8EP

60

0

61218243036

INPUT VOLTAGE

Figure 5 SW R vs. Input Voltage

AL8807A

Document number: DS35990 Rev. 2 - 2

DS(ON)

V = Open

CTRL

V = V

SET IN

T = 25°C

A

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150

100

-40 10 35 60 85 110

-15 AMBIENT TEMPERATURE (°C)

Figure 6 SW R vs. Temperature

DS(ON)

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CUR

REN

T ERRO

R

CUR

RENT

C

URREN

T

Typical Performance Characteristics

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

L8807A

Figure 7 SW Output Rise Time

22%

R = 100m



S

LED Current

(%)

20% 18% 16%

V = 12V

IN

2 LEDs L = 68µH T = 25°C

A

14%

R = 150m



12%

S

10%

8% 6% 4%

LED

2% 0%

-2% 012345

R = 150m

S



LED Current Error

R = 100m

S



CTRL VOLTAGE (V)

Figure 9 LED Current (Different Sense Resistor) vs. V

0.25

V = 12V

IN

2 LEDs R = 100m



S

T = 25°C

A

0.20

1.10

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10

0.00

-0.10

CTRL

Figure 8 SW Output Fall Time

1.2

V = 12V

IN

2 LEDs

1.0

0.8

(A)

R = 100m

S

T = 25°C

A



0.6

L = 33µH

LED CURRENT (A)

0.4

LED

0.2

L = 68 ~ 220µH

0.0 012345

CTRL VOLTAGE (V )

Figure 10 LED Current (Different Inductor) vs. V

CTRL

(A)

0.15

0.10

LED

L = 33µH

0.05

L = 68 ~ 220µH

0.00

0 0.1 0.2 0.3 0.4 0.5

Figure 11 LED Current (Zoomed In) vs. V

AL8807A

Document number: DS35990 Rev. 2 - 2

CTRL

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Figure 12 Switching Frequency vs. V

CTRL

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CTRL PIN VOLT AGE (V)