AL8805
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L8805
HIGH EFFICIENCY 36V 1A BUCK LED DRIVER
Description
The AL8805 is a step-down DC/ DC converter designed to d rive 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 VIN and SET input pins. Dimming is achieved
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.
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)
Pin Assignments
4SET
5V
IN
SW 1
CTRL 3
GND 2
(Top View)
SOT25
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 In corpor ated’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
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
3 CTRL
Dimming and On/Off Control Input.
• Leave floating for normal operation.
(VCTRL = VREF = 2.5V giving nominal average output current IOUTnom = 0.1/RS)
• Drive to voltage below 0.4V to turn off output current
• Drive with DC voltage (0.5V < VCTRL < 2.5V) to adjust output current from 20% to 100% of IOUTnom
• 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 > 2.2µF X7R ceramic capacitor – see applications
section for more information.
Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.)
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
VSET SET Pin Voltage Relative to VIN Pin -5 to +0.3 V
VSW SW Voltage Relative to GND -0.3 to 40 V
VCTRL CTRL Pin Input Voltage -0.3 to 6 V
ISW-DC DC or RMS Switch current 1.25 A
ISW-PK Peak Switch Current (<10%) 2.5 A
TJ Junction Temperature 150 °C
TLEAD Lead Temperature Soldering 300 °C
TST Storage Temperature Ra nge -65 to +150 °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
Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Symbol Parameter Min Max Unit
VIN Operating Input Voltage relative to GND 6.0 36 V
VCTRLH Voltage High for PWM Dimming Relative to GND 2.6 5.5 V
VCTRLDC Voltage Range for 20% to 100% DC Dimming Relative to GND 0.5 2.5 V
VCTRLL Voltage Low for PWM Dimming Relative to GND 0 0.4 V
ISW Continuous Switch Current — 1 A
TJ Junction Temperature Range -40 125 °C
AL8805
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L8805
Electrical Characteristics (VIN = 12, @TA = +25°C, unless otherwise specified.)
Symbol Parameter Conditions Min Typ Max Unit
VINSU Internal Regulator Start Up Threshold VIN rising 5.9 V
VINSH Internal Regulator Hysteresis Threshold VIN falling 100 300 mV
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
VTH-H Set Threshold Hysteresis ±20 mV
ISET SET Pin Input Current VSET = VIN-0.1 16 22 µA
RCTRL CTRL Pin Input Resistance Referred to internal reference 50 kΩ
VREF Internal Reference Voltage 2.5 V
RDS(on) On Resistance of SW MOSFET ISW = 1A 0.25 0.4 Ω
ISW_Leakage Switch Leakage Current VIN = 30V 0.5 μA
fOSC Switching Frequency 1 MHz
θJA Thermal Resistance Junction-to-
Ambient (Note 5) SOT25 (Note 6) 250
°C/W
ΨJB Thermal Resistance Junction-to-Lead
(Note 7) SOT25 50
Notes: 4. AL8805 does not have a low power standby mode but current consumption is reduced when output switch is inhibited: VSENSE = 0V. Parameter is
tested with VCTRL ≤ 2.5V
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
. As SOT25 doesn’t have an exposed tab or exposed pad the majority of heat flow is though pin 2 down to ground.
AL8805
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L8805
Typical Performance Characteristics (@TA = +25°C, unless otherwise specified.)
0
50
100
150
200
250
300
350
400
V (V)
Figure 1 Supply Current (not switching) vs. Input V oltage
IN
I (µA)
IN
V = 0V
V = V
T = 25°C
CRTL
SET IN
A
06
12 18 24 30 36
0
100
200
300
400
500
600
700
800
900
012345
V(V)
Fig ur e 2 Switchin g Fr eq uency vs. V
CTRL
CTRL
F
R
E
Q
U
E
N
C
Y
(kHz)
V = 12V
1 LED
R = 150m
T = 25°C
IN
SET
A
Ω
L = 33µH
L = 68µH
L = 100µH
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
012345
V (V)
Figure 3 LED Current vs. V
CTRL
CTRL
I (A)
LED
V = 12V
1 LED
T = 25°C
IN
A
L = 68µH
R = 100m
SET
Ω
R = 150m
SET
Ω
R = 300m
SET
Ω
-60
-40
-20
0
20
40
60
80
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
V (V)
Figure 4 I vs. V
CTRL
CTRL CTRL
I (µ
A
)
CTRL
V = V = 12V
T = 25°C
SET IN
A
3
2.5
2
1.5
0.5
0
V (V)
CTRL
1
V = Open
V = V
CTRL
SET IN
T = 25°C
A
0 3 6 9 12 18 21 24 27 30 36
V (V)
Figure 5. V vs. Input Voltage
(CTRL P in Open Circuit)
IN
CTRL
15 33
2.48
2.49
2.50
2.51
2.52
-40 -15 10 35 60 85 110
AMBIENT TEMPERA TURE (°C)
Fi g u r e 6 V vs. Tem per ature
CTRL
V (V)
CTRL
V = Open
V = V = 12V
CTRL
SET IN
AL8805
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L8805
Typical Performance Characteristics (cont.) (@TA = +25°C, unless otherwise specified.)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0% 20% 40% 60% 80% 100%
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
LED CURRENT (A)
PWM DUTY CYCLE
F igure 7 I vs. PWM Duty Cycle
LED
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
0
60
120
180
240
300
612 18 24 30 36
V (V)
Figure 8 SW R vs. Input Voltage
IN
DS(ON)
R
(m )
DS(ON)
Ω
V = O pen
V = V
T = 25C
CTRL
SET IN
A
°
100
150
200
250
300
350
400
-40 -15 10 35 60 85 110
AMBIENT TEMPERA TURE (°C)
Figure 9 SW R vs. Temperature
DS(ON)
R(m)
DS(ON)
Ω
80
85
90
95
100
105
110
115
120
125
130
-2
0
2
4
6
8
10
12
14
16
18
TIME (µs)
Figure 10 SW Output Switching Characteristics
V
SW
V(mV)
SENSE
R = 150m
L = 68µH
V = 12V
1 LED Lo ad
SET
IN
Ω
V
SW
V
SENSE
I
LED
V
SW
V
CTRL
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
050100150200
Time (µs)
Figure 1 1 PWM Dimming
0
2
4
6
8
10
12
14
16
18
20
Du ty Cycle = 5%
SW ITCH and CTRL VOLTAGE (V)
LED CURRENT (A)
R = 150m , L =68µH, V = 12V, 1LED Load, T =25 C
SET IN A
Ω°
6912151821242730
INP UT VOLTAGE (V)
Figure 12 Duty Cycle vs. Input Voltage
D
U
T
Y
C
Y
C
LE
L = 33µH
R = 150m
T = 25°C
2 LED
S
A
Ω
33 36
AL8805
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L8805
Typical Performance Characteristics (cont.) (@TA = +25°C, unless otherwise specified.)
80%
82%
84%
86%
88%
90%
92%
94%
96%
98%
100%
6 9 12 15 18 21 24 27 33
INPU T VOLTAGE ( V)
F i gure 13 Effi c ie ncy v s . Input Vo ltag e
EFFI
C
IEN
C
Y
30 36
1 LED
2 LEDs
3 LEDs
4 LEDs 5 LEDs 6 LEDs7 LEDs 8 LEDs
L = 100µH
R = 150m
T = 25°C
S
A
Ω
2 LEDs 4 LEDs
5 L EDs 6 LE Ds 8 LEDs
INP UT VOLTAGE (V)
Figure 14 330m A LED Current v s. In put Voltage
LED
C
U
R
R
ENT (A)
0.30
0.31
0.32
0.33
0.34
0.35
0.36
6 9 12 15 18 21 24 27 30 33 36
1 LED
3 LE Ds
L = 68 H
R = 300m
T = 25C
µ
°
S
A
Ω
7 LEDs
0
50
100
150
200
250
300
350
INPUT VOLTAGE (V)
Figure 15 Switching Frequency vs. Input Voltage
L = 100 H
R = 150m
T = 25C
µ
°
S
A
Ω
SWITCHING FREQUENCY (kHz)
6 9 12 15 18 21 24 27 30 33 36
1 LED
2 LEDs
3 LE Ds 4 LEDs5 LEDs
6 LEDs7 LEDs
8 LEDs
6 9 12 15 18 21 24 27 36
INPUT VOLTAGE (V)
Figure 16 670mA LED Current vs. Input Voltage
LED CURRENT (A)
0.720
30 33
0.710
0.700
0.690
0.680
0.670
0.660
0.650
0.640
0.630
0.620
INP UT VOLTAGE (V)
Figure 17 1A LED Current vs. Input Voltage
L
E
D
C
U
R
R
E
N
T
(
A
)
0.90
0.95
1.00
1.05
1.10
6 9 12 15 18 21 24 27 30 33 36
AL8805
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L8805
Typical Performance Characteristics (cont.) (670mA LED Current) (@TA = +25°C, unless otherwise specified.)
5%
INPUT VOLTAGE (V)
Figure 18 LED Current Deviation vs. Input Voltage
% ER R OR
6 9 12 15 18 21 24 27 30 33 36
4%
3%
2%
1%
0%
-1%
-2%
-3%
-4%
-5%
0
50
100
150
200
250
300
350
INPUT VOLTAGE (V)
Fig ur e 19 Switching Frequency vs. I nput Volta ge
F
R
E
Q
U
E
N
C
Y
(kHz)
L = 100 H
R = 150m
T = 25C
µ
°
S
A
Ω
6 9 12 15 18 21 24 27 30 33 36
1 LED
2 LEDs
3 LEDs 4 LEDs
5 LEDs6 LEDs
7 LEDs
8 LEDs
INP UT VOLTAGE (V)
Figur e 20 L ED Current Deviat ion vs. Input Vol tage
-10%
-8%
-6%
-4%
-2%
0%
2%
4%
6%
8%
10%
%
E
R
R
O
R
6 9 12 15 18 21 24 27 30 33 36
0
50
100
150
200
250
300
350
400
450
500
INPUT VOLTAGE (V )
Figure 21 Switching Frequency vs. Input V oltage
SWITCHING FREQUENCY (kHz)
6 9 12 15 18 21 24 27 30 33 36
-10%
-8%
-6%
-4%
-2%
0%
2%
4%
6%
8%
10
%
INPUT VOLTAGE (V)
Figure 22 LED Current Deviation vs. Input V oltage
%
E
R
R
O
R
69
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 23 Switching Frequency vs. Input V oltage
0
100
200
300
400
500
600
700
800
FREQUENCY (kHz)
6 9 12 15 18 21 24 27 30 33 36
900
AL8805
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Typical Performance Characteristics (cont.) (1A LED Current) (@TA = +25°C, unless otherwise specified.)
2 LEDs
3 LEDs 5 LEDs
6 LEDs 7 L EDs
-8%
-6%
-4%
-2%
0%
2%
4%
6%
8%
10%
INPUT VOLTAGE (V)
Figure 24 LED Current Deviation vs. Input V o ltage
L = 100 H
R = 100m
T = 25C
µ
°
S
A
Ω
% ERROR
-10%6 9 12 15 18 21 24 27 30 33 36
1 LED
4 LEDs
8 LEDs
0
50
100
150
200
250
INP UT VOLTAGE (V)
Figure 25 Switching Frequency vs. Input Voltage
S
WIT
C
H
I
N
G
F
R
E
Q
U
E
N
C
Y
(k
H
z)
9 1215182124273033366
2 LEDs
3 LEDs
-8%
-6%
-4%
-2%
0%
2%
4%
6%
8%
10%
INPUT VOLTAGE (V)
Figure 26 LED Current Deviation vs. Input V oltage
L =68 H
R = 100m
T = 25C
µ
°
S
A
Ω
% ERROR
6 9 12 15 18 21 24 27 30 33 36
8 L EDs
1 LED
4 L EDs
5 LEDs
6 LEDs7 LEDs
1 LED
2 LEDs3 LEDs
4 LEDs 6 LEDs7 LE Ds8 LEDs
0
50
100
150
200
250
300
350
L = 68 H
R = 100m
T = 25C
µ
°
S
A
Ω
INPU T VOLTAGE (V)
Figure 27 Switching Frequency vs. Input Voltage
6 9 12 15 18 21 24 27 30 33 36
5 LEDs
S
WIT
C
HIN
G
F
R
E
Q
UEN
C
Y
(
k
Hz)
1 L ED
2 LEDs
3 LEDs
5 LEDs
6 L EDs
8 L EDs
-8%
-6%
-4%
-2%
0%
2%
4%
6%
8%
10%
INPU T VOLTAGE ( V)
Figure 28 LED Current Deviation vs. Input Voltage
L = 33 H
R = 100m
T = 25C
µ
°
S
A
Ω
% ERROR
-10%6 9 12 15 18 21 24 27 30 33 36
4 LEDs
0
100
200
300
400
500
600
INP UT VOLTAGE (V)
Figure 29 Switching Frequency vs. Input Voltage
700
S
WIT
C
H
I
N
G
F
R
E
Q
U
E
N
C
Y
(k
H
z)
6 9 12 15 18 21 24 27 30 33 36
AL8805
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Application Information
AL8805 Operation
In normal operation, when voltage is applied at +VIN, the AL8805 internal switch is turned on. Current starts to flow through sense resistor R1,
inductor L1, and the LEDs. The current ramps up linearly, and the ramp rate is determined by the input voltage +Vin and the inductor L1.
This rising current produces a voltage ramp across R1. The internal circuit of the AL8805 senses the voltage across R1 and applies a proportional
voltage to the input of the internal comparator.
When this voltage reaches an internally set upper threshold, the in ternal switch is turned off. The inductor current continues to flow through R1,
L1, the LEDs and the schottky diode D1, and back to the supply rail, but it decays, with the rate of decay determined b y the forward voltage drop
of the LEDs and the schottky diode.
This decaying current produces a falling voltage at R1, which is sensed by the AL8805. A voltage proportional to the sense voltage across R1 is
applied at the input of the internal comparator. When this voltage falls to the internally set lo wer threshold, the inte rnal switch is turned on again.
This switch-on-and-off cycle continues to provide the average LED current set by the sense resistor R1.
LED Current Control
The LED current is controlled by the resistor R1 in Figure 30.
Connected between VIN and SET the nominal average output current in the LED(s) is defined as:
SET
THD
LED R
V
I=
If the CTRL pin is driven by an external voltage (higher than 0.4V and lower than 2.5V), the average LED current is:
SET
THD
REF
CTRL
LED R
V
V
V
I=
For example for a desired LED current of 660mA and a default voltage VCTRL=2.5V the resulting resistor is:
Ω≈== m150
5.2 5.2
66.0 1.0
V
V
I
V
RREF
CTRL
LED
THD
SET
Figure 30 Typical Application Circuit
DC Dimming
The CTRL pin can be driven by an external DC voltage (VCTRL), to adjust the output current to a value below the nominal average value defined
by RSET. The LED current decreases linearly with the CTRL voltage when 0.5V ≤ VCTRL ≤ 2.5V, as in Figure 2 for 4 different current levels.
When the CTRL voltage falls below the threshold, 0.4V, the output switch is turned off which allows PWM dimming.
Note that 100% brightness setting corresponds to V CTRL = VREF, nominally 2.5V. For any voltage appl ied on the CTR L pin that is higher than VREF,
the device will not overdrive the LED current and will still set the current according to the equation VCTRL = VREF.
R1
AL8805
1
L1
VIN
SET
SW
CTRL
GND
C1
C2
D1
AL8805
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Application Information (cont.)
PWM Dimming
LED current can be adjusted digitally, by applying a low frequency Pulse Width Modulated (PWM) logic signal to the CTRL pin to turn the device
on and off. This will produce an average output current proportional to the duty cycle of the control signal. In particular, a PWM signal with a
max resolution of 10bit can be applied to the CTRL pin to change the output current to a value below the nominal average value set by resistor
RSET. To achieve this resolution the PWM frequency has to be lower than 500Hz, however higher dimming frequencies can be used, at the
expense of dimming dynamic range and accuracy.
Typically, for a PWM frequency of 500Hz the accuracy is better than 1% for PWM ranging from 1% to 100%.
Figure 31 PWM Dimming at 500Hz
Figure 32 Low Duty Cycle PWM Dimming at 500Hz
The CTRL pin is designed to be driven by both 3.3V and 5V logic
levels directly from a logic output with either an open drain output
or push-pull output stage.
0
100
200
300
400
500
600
700
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
PWM dim ming [%]
LED current [m A
]
0
10
20
30
40
50
60
70
0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10%
PW M dim m ing [%]
LED current [m A
]
µC AL8805
GND
CTRL
µC AL8805
GND
CTRL
AL8805
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Application Information (cont.)
Soft Start
The AL8805 does not have in-built soft-start action – this provides very fast turn off of the output the stage improving PWM dimming accuracy;
nonetheless, adding an external capacitor from the CTRL pin to ground will provide a soft-start delay. This is achieved by increasing the time
taken for the CTRL voltage to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the
comparator. Adding a capacitor increases the time taken for the output to reach 90% of its final value, this delay is 0.1ms/nF, but will impact on
the PWM dimming accuracy depending on the delay introduced.
Figure 33 Soft Start with 22nF Capacitor on CTRL Pin (VIN = 36V, ILED = 667mA, 1 LED)
Reducing Output Ripple
Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a capacitor C2 across the LED(s) as shown already in the
circuit schematic.
A value of 1μF will reduce the supply ripple current by a factor three (approx.). Proportionally lower ripple can be achieved with higher capacitor
values. Note that the capacitor will not affect opera ting frequency or efficiency, but it will increase start-up delay, by reducing the rate of rise of
LED voltage. By adding this capacitor the current waveform through the LED(s) changes from a triangular ramp to a more sinusoidal version
without altering the mean current value.
Capacitor Selection
The small size of ceramic capacitors makes them ideal for AL8805 applications. X5R and X7R types are recommended because they retain their
capacitance over wider voltage and temperature ranges than other types such as Z5U.
A 2.2μF input capacitor is sufficient for most intended applications of AL8805; however a 4.7μF input capacitor is suggested for input voltages
approaching 36V.
AL8805
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Application Information (cont.)
Diode Selection
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode with low reverse leakage at the
maximum operating voltage and temperatu re. Th e Schottky diode also provides better efficienc y than silicon PN diodes, due to a com bination of
lower forward voltage and reduced recovery time.
It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum
output load current. In particular, it is recommended to h ave a diode voltage rating at least 15 % hig her tha n the ope r ating voltage to e nsure safe
operation during the switching and a current rating at least 10% higher than the average diode current. The power rating is verified by
calculating the power loss through the diode.
Schottky diodes, e.g. B240 or B140, with their low forward voltage drop and fast reverse recovery, are the ideal choice for AL8805 applications.
Thermal and Layout Considerations
For continuous conduction mode of operation, the absolute maximum junction temperature must not be exceeded. The maximum power
dissipation depends on several factors: the thermal resistance of the IC package θJA, PCB layout, airflow surrounding the IC, and difference
between junction and ambient temperature.
The maximum power dissipation can be calculated using the following formula:
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum operating junction temperature,
TA is the ambient temperature, and
θJA is the junction to ambient thermal resistance.
The recommended maximum operating junction temperature, TJ, is +125°C and so maximum ambient temperature is determined by the
AL8805’s junction to ambient thermal resistance, θJA.
θJA, is layout dependent and the AL8805’s θJA on a 25 x 25mm single layer PCB with 1oz copper standing in still air is approximatel y +250°C/W
(+160°C/W on a four-layer PCB).
The maximum power dissipation at TA = +25°C can be calculated by the following formulas:
PD(MAX) = (+125°C − +25°C) / (250°C/W) = 0.4W for single-layer PCB
PD(MAX) = (+125°C − +25°C) / (160°C/W) = 0.625W for standard four-layer PCB
Figure 34, shows the power derating of the AL8805 on two (one single-layer and four-layer) different 25x25mm PCB with 1oz copper standing in
still air.
Figure 34 Derating Curve for Different PCB
AL8805
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Application Information (cont.)
Thermal and Layout Considerations
Figure 35 gives details about the PCB layout suggestions:
1. the capacitor C1 has to be placed as close as possible to VIN
2. The sense resistor R1 has to be placed as close as possible to VIN and SET
3. The D1 anode, the SW pin and the inductor have to be placed as close as possible to avoid ringing.
Figure 35 Recommended PCB Layout
Application Example
Typical application example for the AL8805 is the MR16 lamp. The y typically operate from 12VDC or 12VAC, using conventional electromagnetic
transformers or electronic transformers.
As a replacement in some halogen lamp applications LEDs offer a more energy efficient solution – providing no radiated heat and no Ultra Violet
light.
This application example is intended to fit into the base connector space of an MR16 style LED lamp. The design has been optimized for part
count and thermal performance for a single 3W LED in the Lens section.
Figure 36 MR16 Schematic
An inductor choice of 33µH with saturation current higher than 1.1A, will limit the frequency variation between 230kHz and 350kHz over the
whole input voltage variation (8V to 18V), and therefore represent the best choice for an MR16 solution also taking into account the size
constraint of the lamp.
The AL8805 guarantee high level of performance both with 12VAC and 12VDC power supply.
The efficiency is generally higher than 81% and current regulation is better than 0.1mA/V in for a DC input voltage in the range from 8V to 18V.
In table 1 can be found the bill of material of the MR16 application example.
AL8805AL8805
AL8805
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Application Information (cont.)
In Figures 37 and 38 are displayed the top layer and the bottom layer of a typical PCB design for an MR16 solution.
Figure 37 Top Layer
Figure 38 Bottom Layer
Table1 MR16 Application Example Bill of Material
Quantity PCB
Ident Value Description Suggested
Sources
1 U1 AL8805 LED Driver IC Diodes Zetex
1 D1, DFLS240L freewheeling diode Diodes Zetex
4 D2, D3, D4, D5 SBR2A40 Input bridge Diodes Zetex
1 R1 0R15
Resistor, 0805, +/-1% <+/-300ppm Generic
KOA SR732ATTDR150F Kemet
1 C1 150uF 20V SMD tantalum Kemet D case, T491X157K020AT Kemet
0 C2 - Not fitted
1 C3 100nF > = 25V X7R 0805 Generic Kemet C0805C104K5RAC (50v)
NIC NMC0805X7R104K50TRPF (50v) Kemet
NIC Components
1 C4 1uF > = 25V X7R 1206 Generic Kemet C1206105K5RAC7800 (50v)
NIC NMC1206X7R105K50F (50v) Kemet
NIC Components
1 L1 33µH LPS6235 - 333MLB Coilcraft
AL8805
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Ordering Information
AL 8805 W5 - 7
Package Packing
W5 :SOT25 7 : Tape & Reel
Device Package Code
Packaging
(Note 6) 7” Tape and Reel
Quantity Part Number Suffix
AL8805W5-7 W5 SOT25 3000/Tape & Reel -7
Note: 8. 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 .
Marking Information
1 2 3
5
7
4
XX YW X
(Top View)
XX : Identification code
W : Week : A~Z : 1~26 week;
X : A~Z : Intern al code
Y : Year 0~9
a~z : 27~52 week; z represents
52 and 53 week
Part Number Package Identification Code
AL8805W5-7 SOT25 A6
Package Outline Dimensions (All dimensions in mm.)
SOT25
Dim Min Max Typ
A 0.35 0.50 0.38
B 1.50 1.70 1.60
C 2.70 3.00 2.80
D ⎯ ⎯ 0.95
H 2.90 3.10 3.00
J 0.013 0.10 0.05
K 1.00 1.30 1.10
L 0.35 0.55 0.40
M 0.10 0.20 0.15
N 0.70 0.80 0.75
α 0° 8°
⎯
All Dimensions in mm
A
M
JL
D
B C
H
KN
AL8805
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Suggested Pad Layout
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(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
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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 devices or systems, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their pro ducts and an y
use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
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Copyright © 2012, Diodes Incorporated
www.diodes.com
Dimensions Value (in mm)
Z 3.20
G 1.60
X 0.55
Y 0.80
C1 2.40
C2 0.95
X
Z
Y
C1
C2C2
G
