AL8805 - Diodes Incorporated

AL8805
HIGH EFFICIENCY 36V 1A BUCK LED DRIVER
Description
Pin Assignments
The AL8805 is a step-down DC/DC converter designed to drive LEDs
(Top View)
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.
SW
1
GND
2
CTRL
3
5
VIN
4
SET
Maximum output current of AL8805 is set via an external resistor
connected between the VIN and SET input pins. Dimming is achieved
SOT25
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
Applications
•
LED Driving Current up to 1A
•
MR16 Lamps
Better than 5% Accuracy
•
General Illumination Lamps
•
•
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
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
AL8805
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AL8805
Pin Descriptions
Pin Number
Pin Name
1
SW
2
GND
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.
3
CTRL
4
SET
5
VIN
•
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.
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
Junction Temperature
150
°C
TLEAD
TJ
Lead Temperature Soldering
300
°C
TST
Storage Temperature Range
-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
Min
Max
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
VIN
Parameter
AL8805
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AL8805
Electrical Characteristics (VIN = 12, @TA = +25°C, unless otherwise specified.)
Symbol
Parameter
Conditions
VINSU
Internal Regulator Start Up Threshold
VINSH
Internal Regulator Hysteresis Threshold VIN falling
Quiescent Current
Output not switching (Note 4)
IS
Input Supply Current
CTRL pin floating f = 250kHz
Set Current Threshold Voltage
VTH-H
Max
Unit
5.9
V
300
mV
350
µA
1.8
5
mA
100
105
mV
100
95
Set Threshold Hysteresis
ISET
Typ
VIN rising
IQ
VTH
Min
±20
mV
SET Pin Input Current
VSET = VIN-0.1
16
RCTRL
CTRL Pin Input Resistance
Referred to internal reference
50
kΩ
VREF
Internal Reference Voltage
2.5
V
RDS(on)
ISW_Leakage
On Resistance of SW MOSFET
ISW = 1A
Switch Leakage Current
VIN = 30V
fOSC
Switching Frequency
θJA
Thermal Resistance Junction-to-
ΨJB
Thermal Resistance Junction-to-Lead
Notes:
Ambient (Note 5)
(Note 7)
SOT25 (Note 6)
0.25
22
µA
0.4
Ω
0.5
μA
1
MHz
250
°C/W
SOT25
50
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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AL8805
Typical Performance Characteristics (@TA = +25°C, unless otherwise specified.)
400
900
VCRTL = 0V
VSET = VIN
T A = 25°C
350
700
FREQUENCY (kHz)
250
IIN (µA)
VIN = 12V
1 LED
RSET = 150mΩ
TA = 25°C
800
300
200
150
600
L = 68µH
500
400
300
100
200
50
L = 100µH
100
0
0
0
18
30
36
24
VIN (V)
Figure 1 Supply Current (not switching) vs. Input Voltage
6
12
1
0.9
0.8
0
1
2
3
4
5
VCTRL (V)
Figure 2 Switching Frequency vs. VCTRL
80
VIN = 12V
1 LED
L = 68µH
T A = 25°C
VSET = VIN = 12V
T A = 25°C
RSET = 100mΩ
60
40
0.7
RSET = 150mΩ
0.6
ICTRL (µA)
ILED (A)
L = 33µH
0.5
0.4
0.3
20
0
-20
RSET = 300mΩ
0.2
-40
0.1
-60
0
0
1
2
3
4
VCTRL (V)
Figure 3 LED Current vs. VCTRL
5
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)
Figure 4 ICTRL vs. VCTRL
2.52
3
VCTRL = Open
VSET = VIN = 12V
2.5
2.51
VCTRL (V)
VCTRL (V)
2
1.5
2.50
1
2.49
VCTRL = Open
VSET = VIN
T A = 25°C
0.5
0
0
3
6
9 12 15 18 21 24 27 30 33 36
VIN (V)
Figure 5. VCTRL vs. Input Voltage
(CTRL Pin Open Circuit)
AL8805
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2.48
-40
-15
10
35
60
85
AMBIENT TEMPERATURE (°C)
Figure 6 VCTRL vs. Temperature
110
July 2012
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AL8805
4.5
0.9
4.0
0.8
3.5
0.7
3.0
0.6
2.5
0.5
2.0
0.4
1.5
0.3
1.0
0.2
0.5
0.1
0.0
0%
300
240
180
120
VCTRL = Open
VSET = VIN
TA = 25 °C
60
0
40%
60%
80%
100%
PWM DUTY CYCLE
Figure 7 ILED vs. PWM Duty Cycle
0
20%
400
6
12
24
30
36
VIN (V)
Figure 8 SW RDS(ON) vs. Input Voltage
130
R SET = 150mΩ
L = 68µH
VIN = 12V
1 LED Load
125
350
18
120
VSENSE
VSW
VSENSE (mV)
RDS(ON) (mΩ)
250
16
14
12
115
300
18
110
10
105
8
100
6
95
4
90
2
85
0
80
-2
200
VSW
1
RDS(ON) (mΩ)
5.0
LED CURRENT (A)
LED CURRENT ERROR (%)
Typical Performance Characteristics (cont.) (@TA = +25°C, unless otherwise specified.)
150
100
-40
-15
10
35
60
85
110
AMBIENT TEMPERATURE (°C)
Figure 9 SW RDS(ON) vs. Temperature
RSET = 150mΩ, L =68µH, VIN = 12V, 1LED Load, T A =25°C
20
0.9
18
ILED
16
0.8
0.7
14
VSW
0.6
12
0.5
10
0.4
8
0.3
6
0.2
4
VCTRL
0.1
0
0
50
100
150
Time (µs)
Figure 11 PWM Dimming
AL8805
Document number: DS35030 Rev. 4 - 2
L = 33µH
RS = 150m Ω
TA = 25°C
2 LED
DUTY CYCLE
Duty Cycle = 5%
SWITCH and CTRL VOLTAGE (V)
1
LED CURRENT (A)
TIME (µs)
Figure 10 SW Output Switching Characteristics
2
0
200
6
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INPUT VOLTAGE (V)
Figure 12 Duty Cycle vs. Input Voltage
July 2012
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AL8805
Typical Performance Characteristics (cont.) (@TA = +25°C, unless otherwise specified.)
0.36
100%
6 LEDs 7 LEDs
98%
4 LEDs
96%
8 LEDs
5 LEDs
0.35
3 LEDs
2 LEDs
EFFICIENCY
2 LEDs
92%
90%
88%
86%
3 LEDs
LED CURRENT (A)
94%
1 LED
0.34
0.33 1 LED
0.30
6
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 13 Efficiency vs. Input Voltage
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 14 330mA LED Current vs. Input Voltage
L = 100µH
RS = 150mΩ
TA = 25° C
300
0.710
0.700
250
LED CURRENT (A)
SWITCHING FREQUENCY (kHz)
9
0.720
350
200
2 LEDs
150
1 LED
100
6
0.690
0.680
0.670
0.660
0.650
0.640
7 LEDs
6 LEDs
8 LEDs
5 LEDs
3 LEDs 4 LEDs
50
0
L = 68µH
R S = 300m Ω
TA = 25° C
0.31
L = 100µH
RS = 150mΩ
TA = 25°C
80%
6
5 LEDs 6 LEDs
7 LEDs 8 LEDs
0.32
84%
82%
4 LEDs
0.630
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 15 Switching Frequency vs. Input Voltage
0.620
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 16 670mA LED Current vs. Input Voltage
1.10
LED CURRENT (A)
1.05
1.00
0.95
0.90
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 17 1A LED Current vs. Input Voltage
AL8805
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AL8805
Typical Performance Characteristics (cont.) (670mA LED Current) (@TA = +25°C, unless otherwise specified.)
350
5%
L = 100µH
RS = 150m Ω
TA = 25° C
4%
300
3%
FREQUENCY (kHz)
2%
% ERROR
1%
0%
-1%
-2%
250
200
150
2 LEDs
100
1 LED
-3%
50
-4%
-5%
6
5 LEDs
3 LEDs 4 LEDs
0
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 18 LED Current Deviation vs. Input Voltage
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 19 Switching Frequency vs. Input Voltage
8%
450
SWITCHING FREQUENCY (kHz)
500
4%
% ERROR
6
10%
6%
2%
0%
-2%
-4%
-6%
350
300
250
200
150
100
50
0
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 20 LED Current Deviation vs. Input Voltage
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 21 Switching Frequency vs. Input Voltage
900
8%
800
6%
9
700
FREQUENCY (kHz)
4%
% ERROR
6
10%
2%
0%
-2%
-4%
600
500
400
300
-6%
200
-8%
100
-10%
6
9
400
-8%
-10%
6
7 LEDs
6 LEDs
8 LEDs
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 22 LED Current Deviation vs. Input Voltage
AL8805
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0
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 23 Switching Frequency vs. Input Voltage
July 2012
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AL8805
Typical Performance Characteristics (cont.) (1A LED Current) (@TA = +25°C, unless otherwise specified.)
250
10%
6%
SWITCHING FREQUENCY (kHz)
8%
3 LEDs
5 LEDs
2 LEDs
4 LEDs
6 LEDs 7 LEDs
8 LEDs
4%
% ERROR
2%
1 LED
0%
-2%
-4%
-6%
L = 100µH
RS = 100mΩ
TA = 25° C
-8%
-10%
6
150
100
50
0
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 25 Switching Frequency vs. Input Voltage
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 24 LED Current Deviation vs. Input Voltage
9
6%
3 LEDs
5 LEDs
2 LEDs
4 LEDs
6 LEDs 7 LEDs
4%
SWITCHING FREQUENCY (kHz)
8%
8 LEDs
2%
0%
1 LED
-2%
-4%
-6%
L =68µH
RS = 100m Ω
TA = 25° C
-8%
6
L = 68µH
R S = 100m Ω
TA = 25 °C
250
200
150
100
1 LED
50
0
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 27 Switching Frequency vs. Input Voltage
9
6
8 LEDs
6 LEDs 7 LEDs
4 LEDs
2 LEDs 3 LEDs
5 LEDs
9
700
10%
2 LEDs
8%
4 LEDs
SWITCHING FREQUENCY (kHz)
3 LEDs
6 LEDs
5 LEDs
6%
8 LEDs
4%
% ERROR
9
300
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 26 LED Current Deviation vs. Input Voltage
2%
0%
6
350
10%
% ERROR
200
1 LED
-2%
-4%
-6%
-8%
-10%
6
L = 33µH
R S = 100m Ω
T A = 25 °C
600
500
400
300
200
100
0
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 28 LED Current Deviation vs. Input Voltage
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9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 29 Switching Frequency vs. Input Voltage
July 2012
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AL8805
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 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
VIN
CTRL
R1
SET
1
D1
C1
AL8805
C2
L1
GND
SW
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 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.
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%.
700
LED current [mA]
600
500
400
300
200
100
0
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
7%
8%
9%
10%
PWM dimming [%]
Figure 31 PWM Dimming at 500Hz
70
LED current [mA]
60
50
40
30
20
10
0
0%
1%
2%
3%
4%
5%
6%
PWM dimming [%]
Figure 32 Low Duty Cycle PWM Dimming at 500Hz
The CTRL pin is designed to be driven by both 3.3V and 5V logic
µC
levels directly from a logic output with either an open drain output
AL8805
CTRL
or push-pull output stage.
GND
AL8805
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AL8805
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 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 36V.
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AL8805
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 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.
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 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 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
Document number: DS35030 Rev. 4 - 2
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AL8805
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. 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.
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.
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.
AL8805
Document number: DS35030 Rev. 4 - 2
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AL8805
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
Sources
1
U1
AL8805
1
D1,
DFLS240L
freewheeling diode
Diodes Zetex
4
D2, D3, D4, D5
SBR2A40
Input bridge
Diodes Zetex
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. 4 - 2
LED Driver IC
Suggested
Resistor, 0805, +/-1% <+/-300ppm Generic
KOA SR732ATTDR150F
SMD tantalum Kemet D case, T491X157K020AT
Diodes Zetex
Kemet
Kemet
Not fitted
X7R 0805 Generic Kemet C0805C104K5RAC (50v)
NIC NMC0805X7R104K50TRPF (50v)
X7R 1206 Generic Kemet C1206105K5RAC7800 (50v)
NIC NMC1206X7R105K50F (50v)
LPS6235 - 333MLB
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Kemet
NIC Components
Kemet
NIC Components
Coilcraft
July 2012
© Diodes Incorporated
AL8805
Ordering Information
AL 8805 W5 - 7
Device
Package Code
AL8805W5-7
W5
Note:
Package
Packing
W5 :SOT25
7 : Tape & Reel
7” Tape and Reel
Packaging
(Note 6)
Quantity
Part Number Suffix
SOT25
3000/Tape & Reel
-7
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
(Top View)
4
7
5
XX Y W X
1
2
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
Part Number
Package
Identification Code
AL8805W5-7
SOT25
A6
Package Outline Dimensions (All dimensions in mm.)
A
B C
H
K
J
M
N
D
AL8805
Document number: DS35030 Rev. 4 - 2
L
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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
0°
8°
α
⎯
All Dimensions in mm
July 2012
© Diodes Incorporated
AL8805
Suggested Pad Layout
C2
Z
C2
Dimensions Value (in mm)
Z
3.20
G
1.60
X
0.55
Y
0.80
C1
G
C1
C2
Y
2.40
0.95
X
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Copyright © 2012, Diodes Incorporated
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Document number: DS35030 Rev. 4 - 2
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