DIODES AL8805

AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
NEW PRODUCT
Description
Pin Assignments
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 30V. 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
(Top View)
SW
1
GND
2
CTRL
3
LED driving current up to 1A
Better than 5% accuracy
•
MR16 lamps
•
High efficiency up to 98%
•
General illumination lamps
•
Operating input voltage from 6V to 30V
High switching frequency up to 1MHz
PWM/DC input for dimming control
4
SET
Applications
•
•
VIN
SOT25
•
•
5
•
Built-in output open-circuit protection
•
SOT25: Available in “Green” Molding Compound (No Br,
Sb) with lead Free Finish/ RoHS Compliant (Note 1)
Notes:
1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at
http://www.diodes.com/products/lead_free.html.
Typical Application Circuit
AL8805
Document number: DS35030 Rev. 1 - 2
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
NEW PRODUCT
Absolute Maximum Ratings
Symbol
ESD HBM
ESD MM
VIN
VSW
VCTRL
ISW
TJ
TLEAD
TST
Parameter
Human Body Model ESD Protection
Machine Model ESD Protection
Continuous VIN pin voltage relative to GND
SW voltage relative to GND
CTRL pin input voltage
Switch current
Junction Temperature
Lead Temperature Soldering
Storage Temperature Range
Ratings
2.5
200
-0.3~36
-0.3~36
-0.3 ~ 6
1.25
150
300
-65 to +150
Unit
kV
V
V
V
V
A
°C
°C
°C
Caution: The absolute maximum ratings are rated values exceeding which the product could suffer physical damage. These values must therefore not be
exceeded under any condition. 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
Symbol
VIN
VCTRLH
VCTRLDC
VCTRLL
ISW
TJ
Parameter
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
Junction Temperature Range
Min
6.0
2.6
0.5
0
-40
Max
30
5.5
2.5
0.4
1
125
Unit
V
V
V
V
A
°C
Pin Descriptions
Pin Name
Pin Number
SW
1
GND
2
CTRL
3
SET
4
VIN
5
AL8805
Document number: DS35030 Rev. 1 - 2
Descriptions
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 = 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.
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.
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
NEW PRODUCT
Electrical Characteristics
VIN =12V, TA=25oC, unless otherwise specified.
Symbol
Parameter
VINSU
Internal regulator start up threshold
Internal regulator hysteresis
VINSH
threshold
IQ
Quiescent current
IS
Input supply Current
VTH
Set current Threshold Voltage
VTH-H
Set threshold hysteresis
ISET
SET pin input current
RCTRL
CTRL pin input resistance
VREF
Internal Reference Voltage
RDS(on)
On Resistance of SW MOSFET
ISW_Leakage Switch leakage current
fOSC
Switching Frequency
Thermal Resistance Junction-toθJA
Ambient
Notes: 2.
3.
‡
Conditions
Min
Typ.
VIN rising
VIN falling
100
Output not switching‡
CTRL pin floating f = 250kHz
95
VSET = VIN-0.1
Referred to internal reference
ISW = 1A
VIN =30V
SOT25 (Note 3)
1.8
100
±20
16
50
2.5
0.25
Max
5.9
Unit
V
300
mV
350
5
105
µA
mA
mV
mV
µA
kΩ
V
Ω
μA
MHz
22
0.4
0.5
1
°C/W
250
Refer to figure 34 for the device derating curve.
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.
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
AL8805
Document number: DS35030 Rev. 1 - 2
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Typical Performance Characteristics (TA = 25°C unless otherwise stated)
900
400
350
Frequency (kHz)
250
IIN (µA)
VIN = 12V
1 LED
RSET = 150mΩ
TA = 25°C
700
300
VCTRL = 0V
VSET = VIN
TA = 25°C
200
150
NEW PRODUCT
L=33µH
800
100
600
L=68µH
500
400
300
200
L=100µH
50
100
0
0
0
5
10
15
VIN (V)
20
25
30
0
1
2
3
4
5
VCTRL
Figure 1 Supply current (not switching) vs Input voltage
Figure 2. switching frequency vs VCTRL
1
80
VIN = 12V
1 LED
L = 68µH
TA = 25°C
0.9
0.8
0.7
RSET = 100mΩ
VSET = VIN = 12V
TA = 25°C
60
40
0.5
ICTRL (µA)
ILED (A)
0.6
RSET = 150mΩ
0.4
0.3
20
0
-20
RSET = 300mΩ
0.2
-40
0.1
-60
0
0
1
2
VCTRL (V)
3
4
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
VCTRL (V)
5
Figure 3. LED current vs VCTRL
Figure 4. ICTRL vs VCTRL
3
2.52
VCTRL = Open
VSET = VIN = 12V
2.5
2.51
VCTRL (V)
VCTRL (V)
2
VCTRL = Open
VSET = VIN
TA = 25°C
1.5
1
2.50
2.49
0.5
0
0
5
10
15
VIN (V)
20
25
30
2.48
-40
Figure 5. VCTRL vs Input voltage
(CTRL pin open circuit)
AL8805
Document number: DS35030 Rev. 1 - 2
-15
10
35
60
Ambient Temperature (°C)
85
110
igure 6. VCTRL vs temperature
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F
AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Typical Performance Characteristics Continued (TA = 25°C unless otherwise stated)
VIN = 12V
1LED
RSET = 150mΩ
L = 68µH
0.7
3.0
0.6
2.5
0.5
LED Current Error
2.0
0.4
ILED
1.5
0.3
1.0
0.2
0.5
0.1
20%
40%
60%
PWM Duty Cycle
150
80%
VCTRL = Open
VSET = VIN
TA = 25°C
100
50
0
0
100%
0.0
0%
200
0
5
Figure 7. ILED vs PWM duty cycle
10
20
25
130
18
125
350
16
VSENSE
120
14
115
110
250
VCTRL = Open
VSET = VIN = 12V
200
8
100
6
4
RSET = 150mΩ
L = 68µH
VIN = 12V
1LED Load
90
85
100
10
105
95
150
12
VSW
VSENSE (mV)
300
2
0
80
-40
-15
10
35
60
Ambient Temperature (°C)
85
-2
110
0
ILED
VSW
14
12
0.5
10
0.4
8
0.3
6
0.2
VCTRL
0.1
4
2
0
0
50
100
Time (µs)
150
Document number: DS35030 Rev. 1 - 2
8
0
200
L = 33µH
RS = 150mΩ
TA = 25°C
2 LED
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
6
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 12. Duty cycle vs Input voltage
Figure 11. PWM dimming
AL8805
6
100%
Duty Cycle
16
Switch and CTRL voltage (V) .
0.8
0.6
4
Time (µs)
Figure 10. SW Output switching characteristics
RSET = 150mΩ, L = 68µH, VIN = 12V, 1 LED Load, TA = 25°C
1
20
Duty Cycle = 5%
0.9
18
0.7
2
F
igure 9. SW RDS(ON) vs temperature
LED Current (A)
30
Figure 8. SW RDS(ON) vs input voltage
400
RDS(ON) (mΩ)
15
VIN (V)
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VSW
3.5
250
0.8
RDS(ON) (mΩ)
LED Current Error (%)
4.0
0.9
LED Current (A)
4.5
NEW PRODUCT
300
1
5.0
AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Typical Performance Characteristics Continued (TA = 25°C unless otherwise stated)
0.39
100%
L = 100µH
RS = 150mΩ
TA = 25°C
98%
6 LEDs
7 LEDs
8 LEDs
0.37
5 LEDs
4 LEDs
96%
3 LEDs
NEW PRODUCT
0.35
LED Current (A)
Efficiency
94%
2 LEDs
92%
90%
88%
2 LEDs
3 LEDs
0.33
4 LEDs
1 LED
5 LEDs
6 LEDs
7 LEDs 8 LEDs
0.31
L = 68µH
RS = 300mΩ
TA = 25°C
1 LED
86%
84%
0.29
82%
0.27
80%
6
9
12
15
18
21
Input voltage (V)
24
27
6
30
Figure 13. Efficiency vs Input voltage
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 14. 330mA LED current vs Input voltage
0.8
800
L = 68µH
RS = 300mΩ
TA = 25°C
700
500
400
7 LEDs
8 LEDs
300
1 LED
200
5 LEDs
3 LEDs
100
0.7
2 LEDs
1 LED
3 LEDs 4 LEDs
5 LEDs
6 LEDs 7 LEDs 8 LEDs
0.65
L = 68µH
RS = 150mΩ
TA = 25°C
6 LEDs
0.6
4 LEDs
2 LEDs
0.55
0
6
LED Current (A)
Switching frequency (kHz)
0.75
600
9
12
15
18
21
Input voltage (V)
24
27
6
30
Figure 15. Switching frequency vs Input voltage
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 16. 670mA LED current vs Input voltage
1.20
1.15
LED current (A)
1.10
1.05
2 LEDs
3 LEDs
4 LEDs
5 LEDs
6 LEDs 7 LEDs
8 LEDs
1.00
1 LED
0.95
L = 68µH
RS = 100mΩ
TA = 25°C
0.90
0.85
0.80
6
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 17. 1A LED current vs input voltage
AL8805
Document number: DS35030 Rev. 1 - 2
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Typical Performance Characteristics (670mA LED current) (TA = 25°C unless otherwise stated)
10%
350
L = 100µH
RS = 150mΩ
TA = 25°C
8%
300
6%
2 LEDs
3 LEDs
4 LEDs
5 LEDs
6 LEDs
250
8 LEDs
7 LEDs
2%
0%
Freq (kHz)
% Error
4%
1 LED
-4%
150
100
L = 100µH
RS = 150mΩ
TA = 25°C
-6%
1 LED
7 LEDs
50
6 LEDs
-8%
2 LEDs 3 LEDs
6
9
12
15
18
21
Input voltage (V)
24
27
6
30
Figure 18: LED current deviation vs Input voltage
8 LEDs
9
500
8%
450
8 LEDs
6 LEDs
2%
Switching frequency (kHz)
5 LEDs
1 LED
7 LEDs
0%
-2%
L = 68µH
RS = 150mΩ
TA = 25°C
-4%
-6%
15
18
21
Input voltage (V)
24
27
30
L = 68µH
RS = 150mΩ
TA = 25°C
400
2 LEDs 3 LEDs 4 LEDs
4%
12
Figure 19: Switching frequency vs Input voltage
10%
6%
% Error
4 LEDs
5 LEDs
0
-10%
350
300
250
200
150
1 LED
100
6 LEDs
50
-8%
2 LEDs 3 LEDs 4 LEDs
7 LEDs
8 LEDs
5 LEDs
0
-10%
6
9
12
15
18
21
Input voltage (V)
24
27
6
30
Figure 20: LED current deviation vs Input voltage
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 21: Switching frequency vs Input voltage
10%
800
8%
L = 33µH
RS = 150mΩ
TA = 25°C
700
6%
2 LEDs 3 LEDs
4 LEDs
600
5 LEDs
500
2%
6 LEDs
7 LEDs
8 LEDs
0%
1 LED
-2%
400
300
L = 33µH
RS = 150mΩ
TA = 25°C
-4%
Freq (kHz)
4%
% Error
NEW PRODUCT
-2%
200
1 LED
200
7 LEDs
-6%
8 LEDs
6 LEDs
100
-8%
3 LEDs
2 LEDs
4 LEDs 5 LEDs
0
-10%
6
9
12
15
18
21
Input voltage (V)
24
27
Figure 22: LED current deviation vs Input voltage
AL8805
Document number: DS35030 Rev. 1 - 2
30
6
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 23: Switching frequency vs Input voltage
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Typical Performance Characteristics (1A LED current) (TA = 25°C unless otherwise stated)
10%
250
8%
6%
3 LEDs
200
6 LEDs
7 LEDs
Switching frequency (kHz)
4 LEDs 5 LEDs
2 LEDs
4%
8 LEDs
2%
% Error
1 LED
0%
L = 100µH
RS = 100mΩ
TA = 25°C
-6%
150
100
1 LED
50
-8%
3 LEDs
2 LEDs
6
9
12
15
18
21
Input voltage (V)
24
27
6
30
Figure 24: LED current deviation vs Input voltage
8 LEDs
5 LEDs 6 LEDs 7 LEDs
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 25: Switching frequency vs Input voltage
10%
350
8%
L = 68µH
RS = 100mΩ
TA = 25°C
300
6%
2 LEDs
3 LEDs 4 LEDs 5 LEDs
6 LEDs 7 LEDs 8 LEDs
Switching frequency (kHz)
4%
2%
% Error
4 LEDs
0
-10%
1 LED
0%
-2%
L = 68µH
RS = 100mΩ
TA = 25°C
-4%
250
200
150
100
1 LED
-6%
50
-8%
2 LEDs
-10%
4 LEDs 5 LEDs
3 LEDs
8 LEDs
6 LEDs 7 LEDs
0
6
9
12
15
18
21
Input voltage (V)
24
27
30
6
Figure 26: LED current deviation vs Input voltage
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 27: Switching frequency vs Input voltage
10%
600
L = 33µH
RS = 100mΩ
TA = 25°C
8%
500
6%
2 LEDs
3 LEDs
4 LEDs
5 LEDs 6 LEDs
Switching frequency (kHz)
4%
7 LEDs 8 LEDs
2%
% Error
NEW PRODUCT
-2%
-4%
L = 100µH
RS = 100mΩ
TA = 25°C
0%
1 LED
-2%
-4%
L = 33µH
RS = 100mΩ
TA = 25°C
-6%
400
300
200
1 LED
100
7 LEDs
-8%
2 LEDs
3 LEDs 4 LEDs
5 LEDs
8 LEDs
6 LEDs
0
-10%
6
9
12
15
18
21
Input voltage (V)
24
27
Figure 28: LED current deviation vs Input voltage
AL8805
Document number: DS35030 Rev. 1 - 2
6
30
9
12
15
18
21
Input voltage (V)
24
27
30
Figure 29: Switching frequency vs Input voltage
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Applications Information
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 internal 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 by 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 lower threshold, the internal 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:
ILED =
VTHD
RSET
If the CTRL pin is driven by an external voltage (higher than
0.4V and lower than 2.5V), the average LED current is:
ILED =
VCTRL VTHD
VREF R SET
For example for a desired LED current of 660mA and a
default voltage VCTRL=2.5V the resulting resistor is:
R SET =
VTHD VCTRL
0 .1 2 .5
=
≈ 150mΩ
ILED VREF
0.66 2.5
AL8805
Document number: DS35030 Rev. 1 - 2
VIN
CTRL
R1
SET
D1
C1
1
NEW PRODUCT
AL8805 Operation
AL8805
C2
L1
GND
SW
Figure 30: Typical Application Curcuit
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
VCTRL= VREF, nominally 2.5V. For any voltage applied on the
CTRL 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.
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.
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Applications Information (cont.)
PWM Dimming (cont.)
Typically, for a PWM frequency of 500Hz the accuracy is
better than 1% for PWM ranging from 1% to 100%.
700
LED current [mA]
500
400
300
200
100
0
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
7%
8%
9%
10%
PWM dimming [%]
Figure 30. PWM Dimming at 500Hz
70
60
LED current [mA]
NEW PRODUCT
600
50
40
30
20
10
0
0%
1%
2%
3%
4%
5%
6%
PWM dimming [%]
Figure 31. Low duty cycle PWM Dimming at 500Hz
AL8805
Document number: DS35030 Rev. 1 - 2
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Applications Information (cont.)
PWM Dimming (cont.)
Soft Start
NEW PRODUCT
The PWM 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.
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 softstart 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 32. Soft start with 22nF capacitor on CTRL pin (VIN = 30V, ILED = 667mA, 1 LED)
AL8805
Document number: DS35030 Rev. 1 - 2
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Applications Information (cont.)
where
NEW PRODUCT
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 operating 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 30V.
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
temperature. The Schottky diode also provides better
efficiency than silicon PN diodes, due to a combination 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 have a diode voltage rating at least
15% higher than the operating voltage to ensure 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.
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
25x25mm single layer PCB with 1oz copper standing in still
air is approximately 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 singlelayer 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.
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.
Figure 34. Derating Curve for different PCB
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.
The maximum power dissipation can be calculated using the
following formula:
PD(MAX) = (TJ(MAX) − TA) / θJA
AL8805
Document number: DS35030 Rev. 1 - 2
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Applications Information (cont.)
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.
NEW PRODUCT
In table 1 can be found the bill of material of the
MR16 application example.
In figures 37 and 38 are displayed the top layer and the
bottom layer of a typical PCB design for an MR16 solution.
Figure 35. Recommended PCB Layout
Application Example
Typical application example for the AL8805 is the
MR16 lamp. They 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 37. Top Layer
AL8805
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.
AL8805
Document number: DS35030 Rev. 1 - 2
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Figure 38. Bottom Layer
September 2010
© Diodes Incorporated
AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Application Information (cont.)
NEW PRODUCT
Table 1. MR16 application example Bill of Material
QUANTITY
PCB IDENT
VALUE
1
1
4
U1
D1,
D2, D3, D4, D5
AL8805
DFLS240L
SBR2A40
1
R1
0R15
1
C1
150uF 20V
0
C2
-
1
C3
100nF >=25V
1
C4
1uF >=25V
1
L1
33µH
AL8805
Document number: DS35030 Rev. 1 - 2
DESCRIPTION
LED Driver IC
freewheeling diode
Input bridge
Resistor, 0805, +/-1% <+/-300ppm Generic
KOA SR732ATTDR150F
SMD tantalum Kemet D case, T491X157K020AT
SUGGESTED
SOURCES
Diodes Zetex
Diodes Zetex
Diodes Zetex
Kemet
Kemet
Not fitted
X7R 0805 Generic Kemet C0805C104K5RAC (50v)
NIC NMC0805X7R104K50TRPF (50v)
Kemet
NIC Components
X7R 1206 Generic Kemet C1206105K5RAC7800 (50v)
Kemet
NIC NMC1206X7R105K50F (50v)
NIC Components
LPS6235 - 333MLB
Coilcraft
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AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Ordering Information
AL 8805 W5 - 7
W5 :SOT25
7 : Tape & Reel
AL8805W5-7
Packaging
(Note 4)
SOT25
7” Tape and Reel
Quantity
Part Number Suffix
3000/Tape & Reel
-7
4. 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) SOT25
(Top View)
5
4
7
NEW PRODUCT
Packing
Package
Code
W5
Device
Notes:
Package
XX Y W X
1
2
Part Number
AL8805W5-7
3
XX : Identification code
Y : Year 0~9
W : Week : A~Z : 1~26 week;
a~z : 27~52 week; z represents
52 and 53 week
X : A~Z : Internal code
Package
SOT25
Identification Code
A6
Package Outline Dimensions (All Dimensions in mm)
(1) Package Type: SOT25
AL8805
Document number: DS35030 Rev. 1 - 2
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September 2010
© Diodes Incorporated
AL8805
HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
IMPORTANT NOTICE
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DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
NEW PRODUCT
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changes without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability
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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
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Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or
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concerning their products and any use of Diodes Incorporated products in such safety-critical, life support devices or systems,
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Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes
Incorporated products in such safety-critical, life support devices or systems.
Copyright © 2010, Diodes Incorporated
www.diodes.com
AL8805
Document number: DS35030 Rev. 1 - 2
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