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AL8808 Datasheet
COST EFFECTIVE LOW EMI 30V 1A BUCK LED DRIVER

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AL8808
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 VIN and SET input pins. Dimming is achieved
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.
Applications
MR16 Lamps
General Illumination Lamps
Pin Assignments
(Top View)
SW 1
GND 2
5 VIN
CTRL 3
4 SET
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)
ƒ Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
ƒ 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.
Typical Applications Circuit
AL8808
Document number: DS35648 Rev. 2 - 2
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January 2013
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AL8808 Datasheet
COST EFFECTIVE LOW EMI 30V 1A BUCK LED DRIVER

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AL8808
Pin Descriptions
Pin Number
1
2
Pin Name
SW
GND
3 CTRL
4 SET
5 VIN
Function
Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI.
GND Pin
Dimming and On/Off Control Input.
Leave floating for normal operation.
(VCTRL = 5V, Gives nominal average output current IOUTnom = 0.1/RS)
Drive to voltage below 0.4V to turn off output current
Drive with an analog voltage (0.5V < VCTRL < 2.5V) to adjust output current from 20% to 100% of
IOUTnom
Drive with an analog voltage > 2.6V output current will be 100% of IOUTnom
A PWM signal (low level 0.4V and high level > 2.6; transition times less than 1µs) allows the output
current to be adjusted below the level set by the resistor connected to SET input pin.
Set Nominal Output Current Pin. Configure the output current of the device.
Input Supply Pin. Must be locally decoupled to GND with > 2.2µF X7R ceramic capacitor – see applications
section for more information.
Functional Block Diagram
Figure 1. AL8808 Block Diagram
Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.)
Symbol
ESD HBM
ESD MM
VIN
VSET
VSW
VCTRL
ISW
TJ
TLEAD
TST
Parameter
Human Body Model ESD Protection
Machine Model ESD Protection
Continuous VIN pin voltage relative to GND
SET pin voltage relative to VIN pin
SW voltage relative to GND
CTRL pin input voltage
Switch current
Junction Temperature
Lead Temperature Soldering
Storage Temperature Range
Ratings
2.5
200
-0.3 to +33
-5 to +0.3
-0.3 to +33
-0.3 to +6
1.25
150
300
-55 to +150
Unit
kV
V
V
V
V
V
A
°C
°C
°C
Caution:
Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only;
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.
AL8808
Document number: DS35648 Rev. 2 - 2
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January 2013
© Diodes Incorporated


AL8808 Datasheet
COST EFFECTIVE LOW EMI 30V 1A BUCK LED DRIVER

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AL8808
Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Symbol
Parameter
Min
VIN
VCTRLH
VCTRLDC
VCTRLL
ISW
fSW
TJ
Operating Input Voltage Relative to GND
Voltage High for PWM Dimming Relative to GND
Voltage Range for 20% to 100% DC Dimming Relative to GND
Voltage Low for PWM Dimming Relative to GND
Continuous Switch Current (Note 4)
Maximum Switching Frequency
Junction Temperature Range
6.0
2.6
0.5
0
-40
Note:
4. Subject to ambient temperature, input voltage and switching frequency. See applications section for suggested derating.
Max
30
5.5
2.5
0.4
1
1
+125
Unit
V
V
V
V
A
MHz
°C
Electrical Characteristics (@ TA = +25°C, VIN = 12V, CTRL pin floating; unless otherwise specified.)
Symbol
Parameter
Conditions
Min Typ Max Unit
VINSU
VINSH
IQ
IS
VTH
VTH-H
ISET
VCTRL
RCTRL
VREF
RDS(on)
ISW_Lkg
tR
tF
TOTP
TOTP-Hyst
θJA
θJL
θJT
Internal Regulator Start Up Voltage
Internal Regulator Hysteresis Threshold
Quiescent Current
Input Supply Current
Set Current Threshold Voltage
Set Threshold Hysteresis
SET Pin Input Current
Open Circuit CTRL Pin Voltage
CTRL Pin Input Resistance
Internal Reference Voltage
On Resistance of SW MOSFET
Switch Leakage Current
SW Rise Time
SW Fall Time
Over-Temperature Shutdown
Over-Temperature Hysteresis
Thermal Resistance Junction-to-Ambient
Thermal Resistance Junction-to-Lead
Thermal Resistance Junction-to-Top
VIN rising
VIN falling
VIN = 30V, output not switching
fSW = 250kHz
VSET = VIN -0.1
Referred to internal 5V regulator.
ISW = 0.35A
VIN = 30V, VCTRL = 0.4V, VSENSE = 0V
VSENSE = 100 ±20mV, fSW = 250kHz
VSW = 0.1V to 12V to 0.1V, CL = 15pF
TSOT25 (Note 5)
TSOT25 (Note 5)
TSOT25 (Note 5)
5.6 V
200 mV
350 µA
450 µA
95 100 105 mV
±20 mV
16 µA
5V
50 k
2.5 V
0.35
0.5 µA
7 ns
5 ns
145 °C
10 °C
209
57 °C/W
13
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
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January 2013
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AL8808 Datasheet
COST EFFECTIVE LOW EMI 30V 1A BUCK LED DRIVER

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AL8808
Typical Performance Characteristics (@ TA = +25°C, unless otherwise stated.)
400
350
300
250
200
150
100
50
VCTRL = 0V
VSET = VIN
TA = +25°C
0
0 3 6 9 12 15 18 21 24 27 30
INPUT VOLTAGE (V)
Figure 2. Supply Current vs. Input Voltage
1.2
TA = +25°C
1.0
VIN = 12V
L = 68µH
1 LED
RSET = 100mΩ
0.8 RSET = 150mΩ
0.6
0.4
RSET = 300mΩ
0.2
900
800
L = 33µH
700
600
TA = +25°C
VIN = 12V
RSET = 150mΩ
1 LED
500
400
L = 68µH
300
200
100
L = 100µH
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
VCTRL (V)
Figure 3. Switching Frequency vs. VCTRL
20
TA = +25°C, VIN = 12V
0 L = 68µH, RSET = 150mΩ
1 LED
-20
-40
-60
-80
-100
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
VCTRL (V)
Figure 4. LED Current vs. VCTRL
6 0.9
TA = +25°C, VIN = 12V
L = 68µH, RSET = 150mΩ
5 1 LED, fPWM = 500Hz
4 0.6
3
2 0.3
1
0 0.0
0 20 40 60 80 100
PWM DUTY CYCLE (%)
Figure 6. ILED vs. PWM Duty Cycle
-120
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
VCTRL (V)
Figure 5. ICTRL vs. VCTRL
100
90
80
70
60
50
40
30
20
10
TA = +25°C, RSET = 150mΩ
L = 33µH, L = 68µH, L = 100µH
0
6 9 12 15 18 21 24 27
INPUT VOLTAGE VCTRL (V)
Figure 7. Duty Cycle vs. Input Voltage
30
AL8808
Document number: DS35648 Rev. 2 - 2
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AL8808 Datasheet
COST EFFECTIVE LOW EMI 30V 1A BUCK LED DRIVER

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AL8808
Typical Performance Characteristics (cont.) (@ TA = +25°C, unless otherwise stated.)
600
500
VCTRL = Open
VSET = VIN = 12V
400
300
200
100
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
AMBIENT TEMPERATURE (°C)
Figure 8. SW RDS(ON) vs. Temperature
0.50
0.45
0.40
VIN = 12V
VSET = VIN
TA = +25°C
CTRL = Floating
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
200 400 600 800 1000
SWITCH CURRENT (mA)
Figure 10. SW RDS(ON) vs. Switch Current
400
350
300
250
200
150
100
VCTRL = Open
50 VSET = VIN
TA = 25°C
0
6 9 12 15 18 21 24 27
VIN (V)
Figure 9. SW RDS(ON) vs. Input Voltage
30
Figure 11. SW Output Fall Time
Figure 12. Steady State Waveforms
AL8808
Document number: DS35648 Rev. 2 - 2
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Figure 13. SW Output Rise Time
January 2013
© Diodes Incorporated


AL8808 datasheets pdf
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