AL8807
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A
L8807
HIGH EFFICIENCY LOW 36V 1A BUCK LED DRIVER
Description
The AL8807 is a step-down DC/ DC converter designed to d rive LEDs
with a constant current. The device can drive up to 9 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 AL8807 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 AL8807 is set via an external resistor
connected between the VIN and SET input pins. D imming 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 1.3A (MSOP-8EP)
Better Than 5% Accuracy
High Efficiency up to 96%
Optimally Controlled Switching Speeds
Operating Input Voltage from 6V to 36V
PWM/DC Input for Dimming Control
Built-In Output Open-Circuit Protection
SOT25, MSOP-8EP: Available in “Green” Molding Compound
(No Br, Sb)
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Pin Assignments
SOT25
(Top View)
SW
GND
CTRL SET
V
IN
(Top View)
MSOP-8EP
SET
GND
GND
CTRL
V
IN
N/C
SW
SW
Applications
MR16 Lamps
General Illumination Lamps
12V Powered LED Lamps
24V Powered LED 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/quality/lead_free.html 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 tho se which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
Typical Applications Circuit
100 nF
C1 1µF
C4
D1
DFLS2100
D2
DFLS2100
D3
DFLS 2100
D5
DFLS 2100
D4
DFLS2100
GND
SW
GND
CTRL
SET
V
IN
U1
AL8807
0R15
R1
L1
33µH
100nFC5
150µF
C2
150µF
C3
P1
P2
A
NODE
CATHODE
AL8807
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L8807
Pin Descriptions
Pin Name Pin Number Function
SOT25 MSOP-8EP
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
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 4 1 Set Nominal Output Current Pin. Configure the output current of the device.
VIN 5 8
Input Supply Pin. Must be locally decoupled to GND with > 2.2µF X7R ceramic capacitor – see applications
section for more information.
EP — EP
Exposed pad/TAB connect to GND and thermal mass for enhanced thermal impedance. Should not be
used as electrical ground conduction path.
N/C — 7 No Connection
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
VSW SW Voltage Relative to GND -0.3 to +40 V
VCTRL CTRL Pin Input Voltage -0.3 to +6 V
ISW-RMS DC or RMS Switch Current SOT25 1.25
A
MSOP-8EP 1.6
ISW-PK Peak Switch Current (<10%) 2.5 A
TJ Junction Temperature 150 °C
TLEAD 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 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
fSW Maximum Switching Frequency 1 MHz
ISW Continuous Switch Current SOT25 1
A
MSOP-8EP 1.3
TJ Junction Temperature Range -40 +125 °C
AL8807
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L8807
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
tR SW Rise Time VSENSE = 100±20mV, fSW = 250kHz
VSW = 0.1V to 12V to 0.1V, CL = 15pF 12 ns
tF SW Fall Time 20 ns
ISW_Leakage Switch Leakage Current VIN =30V 0.5 μA
JA Thermal Resistance Junction-to-Ambient (Note 5) SOT25 (Note 6) 250
C/W
MSOP-8EP (Note 7) 69
JL Thermal Resistance Junction-to-Lead (Note 8) SOT25 (Note 6) 50
JC Thermal Resistance Junction-to-case (Note 9) MSOP-8EP (Note 7) 4.3
Notes: 4. AL8807 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 35 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. 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
8. Dominant conduction path via Gnd pin (pin 2).
9. Dominant conduction path via exposed pad.
AL8807
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L8807
Typical Performance Characteristics
400
350
100
0
I (µA)
IN
300
50
V = 0V
V = V
T = 25°C
CTRL
SET IN
A
250
150
200
0 3 6 9 15 18 21 24 27 30 33
V (V)
Figure 1. Supply Current (not switching) vs.
Input Vo ltage
IN
12 36
900
800
200
0
F
R
E
Q
U
E
N
C
Y
(k
H
z)
700
100
600
300
400
01234
V
Fi gur e 2. Swit chi ng Fr equ ency vs. V
CTRL
CTRL
5
500
V = 12V
1 LED
R = 150m
T = 25°C
IN
SET
A
L = 33µH
L = 68µH
L = 100µH
100
90
70
60
40
30
20
0
LED
C
U
R
R
E
N
T
(A)
0.0 0.5 1.0 1.5 2.0 3.0 3.5 4.0 4.5 5.0 5.5
CTRL PIN VOLTAGE (V)
Figure 3. LED Current vs. V
CTRL
2.5
0.0 0.5 1.0 1.5 2.5 3.0 3.5 4.0 4.5 5.0
V (V)
Fi gur e 4. I vs. V
CTRL
CTRL CTRL
2.0 5.0
80
60
-40
-60
I (µA)
CTRL
40
-20
0
20
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)
F igur e 5. V vs . In p ut Voltage
(CTRL P in Open Circuit)
IN
CTRL
15 33
-40 -15 10 35 60 85 110
AMBIENT TEMPERA TURE (°C)
Figure 6. V VS. TEMPERATURE
CTRL
2.52
2.51
2.50
2.49
2.48
V (V)
CTRL
V = Open
V = V= 12V
CTRL
SET IN
AL8807
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L8807
Typical Performance Characteristics (cont.)
LED Current
LED Current
Error
L = 68H, R = 150m
T = 25C, V = 12V
CTRL = PWM, f = 500Hz
1 LED
S
AIN
PWM
020406080100
PWM DUTY CYCLE
Figure 7. I vs. PWM Duty Cycle
LED
9
8
7
6
4
3
2
0
LED CURRENT ERROR (%)
5
1
0.8
LED CURRENT (A)
0.7
0.6
0.5
0
0.4
0.3
0.2
0.1
6 9 12 18 21 24 27 30 36
V (V)
Figure 8. SW R vs. Input Voltage
IN
DS(ON)
15 33
300
270
210
150
30
0
R
(m )
DS(ON)
90
240
180
120
60
V = Open
V = V
CTRL
SET IN
T = 25°C
A
-40 -15 35 60 11010 85
Am bi ent Temperatu re ( C)
Fi gur e 9. SW R v s. Tem per atur e
DS(ON)
V = Open
V = V= 12V
CTRL
SET IN
400
250
150
100
R
(m )
DS(ON)
350
300
200
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Figure 10. Duty Cycle vs. Input Voltage
100
90
80
70
60
40
30
20
10
0
50
D
U
T
Y
C
Y
C
LE ( % )
2 LEDS
3 LEDS
L = 68µH
R = 100m
T = 25°C
V = Open
S
A
CTRL
Figure. 11 SW Output Rise Time Figure. 12 SW Output Fall Time
AL8807
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L8807
Typical Performance Characteristics (cont.) (670LED Current)
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 13. LED Curr ent Devi at ion vs. In put Voltage
10
8
2
0
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
4
-4
-6
-2
6
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 14. Swi t ching Frequenc y vs. Input Voltage
350
300
200
50
0
SWI
T
C
H
IN
G
F
R
E
Q
U
EN
C
Y
(k
H
z)
250
100
150
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 15. LED Curr ent Devi at ion vs. In put Voltage
10
8
2
0
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
4
-4
-6
-2
6
6 9 12 15 18 21 24 27 30 33 36
INPU T VOLTAGE (V)
Fig ur e 16. Switching Fr equency vs. Input Voltage
500
450
300
250
50
0
SWI
T
C
H
IN
G
F
R
E
Q
U
EN
C
Y
(k
H
z)
350
150
100
200
400
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Figure 17. LED Current Deviation vs. Input V oltage
10
8
4
2
0
-4
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
1 LED
2 LEDs
3 LEDs
4 LEDs
5 LEDs6 LEDs7 LEDs 8 LEDs
L = 33µH
R = 150m
T = 25°C
V = Open
S
A
CTRL
6
-2
-6
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Figure 18. Switching Frequency vs. Input Voltage
800
700
500
400
100
0
SWI
T
C
H
IN
G
F
R
E
Q
U
EN
C
Y
(k
H
z)
1 LED
2 LEDs
3 LEDs4 LEDs
5 LEDs
6 LEDs
7 LEDs 8 LEDs
L = 33µH
R = 150m
T = 25°C
V = Open
S
A
CTRL
600
300
200
AL8807
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L8807
Typical Performance Characteristics (cont.) (1A LED Current MSOP-8EP)
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 19. LED Curr ent Devi at ion vs. In put Voltage
10
8
2
0
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
4
-4
-6
-2
6
5 LEDs6 LEDs7 LEDs8 LEDs
L = 100µH
R = 100m
T = 25°C
V = Open
S
A
CTRL
2 LEDs3 LEDs
4 LEDs
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Figure 20. Switching Frequency vs. Input Voltage
350
300
200
0
SWI
T
C
H
IN
G
F
R
E
Q
U
EN
C
Y
(k
H
z)
250
50
150
1 LED
100
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 21. LED Curr ent Devi at ion vs. In put Voltage
10
8
2
0
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
4
-4
-6
-2
6
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE ( V)
Figure 22. Switching Frequency vs. Input Voltage
350
300
200
0
SWI
T
C
H
I
N
G
F
R
E
Q
U
E
N
C
Y
(k
H
z)
250
50
150
100
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 23. LED Curr ent Devi at ion vs. In put Voltage
10
8
2
0
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
4
-4
-6
-2
6
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 24. Swi t ching Frequenc y vs. Input Volt age
600
500
300
0
SWI
T
C
H
I
N
G
F
R
E
Q
U
E
N
C
Y
(k
H
z)
400
100
200
AL8807
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L8807
Typical Performance Characteristics (cont.) (1.3A LED Current MSOP-8EP)
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 25. LED Curr ent Devi at ion vs. In put Voltage
10
8
2
0
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
4
-4
-6
-2
6
5 LEDs6 LEDs7 LEDs 8 LEDs
L = 100µH
R = 77m
T = 25°C
V = Open
S
A
CTRL
2 LEDs3 LEDs
4 LEDs
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Figure 26. Sw itching Fr equenc y vs. Input Voltage
250
200
100
0
SWI
T
C
H
IN
G
F
R
E
Q
U
EN
C
Y
(k
H
z)
150
1 LED
50
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 27. LED Curr ent Devi at ion vs. In put Voltage
10
8
2
0
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
4
-4
-6
-2
6
5 LEDs
6 LEDs7 LEDs8 LEDs
L = 68µH
R = 77m
T = 25°C
V = Open
S
A
CTRL
2 LEDs3 LEDs4 LEDs
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Figure 28. Switching Frequency vs. Input Voltage
300
250
150
0
SWI
T
C
H
IN
G
F
R
E
Q
U
EN
C
Y
(k
H
z)
200
100
1 LED
50
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE (V)
Fig ur e 29. LED Curr ent Devi at ion vs. In put Voltage
10
8
2
0
-8
-10
LED
C
U
R
R
EN
T
E
R
R
O
R
(%)
4
-4
-6
-2
6
5 LEDs
6 LEDs7 LEDs8 LEDs
L = 33µH
R = 77m
T = 25°C
V = Open
S
A
CTRL
2 LEDs3 LEDs4 LEDs
6 9 12 15 18 21 24 27 30 33 36
INP UT VOLTAGE ( V)
Figure 30. Switching Frequency vs. Input Voltage
600
500
300
0
SWI
T
C
H
I
N
G
F
R
E
Q
U
E
N
C
Y
(k
H
z)
400
200
1 LED
100
AL8807
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L8807
Application Information
The AL8807 is a hysteretic (also known as equal ripple) LED driver with integrated power s witch. It is available in two packages that provide a PC B
area-power dissipation capability compromise. It is recommended that at higher LED currents/smaller PCBs that the MSOP-8EP vers ion is used to
maximize the allowable LED current over a wider ambient temperature range.
AL8807 Operation
In normal operation, when voltage is applied at +VIN, the AL8807 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 acros s R1. The internal circuit of the AL8807 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 deca ys, with the rate of decay determined b y the forward voltag e drop of th e
LEDs and the schottky diode.
This decaying current produces a falling voltage at R1, which is sensed by the AL8807. 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.
Figure 30 Typical Application Circuit
Connected between VIN and SET the nominal average output current in the LED(s) is defined as:
1R
V
ITHD
LED
For example for a desired LED current of 660mA and a default voltage VCTRL=2.5V the resulting resistor is:
m150
66.0 1.0
I
V
1R LED
THD
DC Dimming
Further control of the LED current can be achieved by driving the CTRL pin with an external voltage (between 0.4V and 2.5V); the average LED
current becomes:
SET
THD
REF
CTRL
LED R
V
V
V
I
With 0.5V ≤ VCTRL ≤ 2.5V the LED current varies linearly with VCTRL, as in figure 2. If the CTRL pin is brought higher than 2.5V, the LED current will
be clamped to approximately 100% and follows SET
THD
LED R
V
I.
When the CTRL voltage falls below the threshold, 0.4V, the output switch is turned off which allows PWM dimming.
AL8807
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Application Information (cont.)
PWM Dimming
LED current can be adjusted digitally, by applying a lo w frequenc y Pulse Width Modulated (PWM) logic signal to the CTRL pin to t urn the device o n
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 CTR L pin to change the o ut put 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%.
0
100
200
300
400
500
600
700
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
PWM dimm in g [%]
LED current [m A
]
Figure 31 PWM Dimming at 500Hz
Zooming in at duty cycles below 10% shows:
Figure 32 Low Duty Cycle PWM Dimming at 300Hz
The accuracy of the low duty cycle dimming is affected by both the PWM frequency and also the switching frequency of the AL8807. For best
accuracy/resolution the switching frequency should be increased while the PWM frequency should be reduced.
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.
AL8807
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Application Information (cont.)
Soft Start
The AL8807 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 = 30V, ILED = 667mA, 1 LED)
Reducing Output Ripple
Peak to peak ripple current in the LED(s) can be reduced, if r equired, by shunting a capacitor C2 across the LED(s) as sho wn 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 frequenc y or efficiency, but it will increase start-up delay, by re ducing the rate o f rise of LE D
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 AL8807 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 AL8807; however a 4.7μF input capacitor is suggested for input voltages
approaching 36V.
AL8807
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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 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 ra ting above th e p eak coil current a nd a continu ous current rating higher th an th e ma ximum outpu t
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 AL8807 applications.
Inductor Selection
Recommended inductor values for the AL8807 are in the range 33μH to 100μH.
Higher values of inductance are recommended at higher supply voltages in order to minimize errors due to switching delays, which result in
increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current over the supply voltage range.
(See graphs).
Figure 34 Inductor value with input voltage and number of LEDs
The inductor should be mounted as close to the device as possible with low resistance/stray inductance connections to the SW pin.
The chosen coil should have a saturation current higher than the peak output current and a continuous current rating above the required mean
output current.
Suitable coils for use with the AL8807 are listed in the table below:
Part No. L
(µH) DCR
(V) ISAT
(A) Manufacturer
MSS1038-333 33 0.093 2.3
CoilCraft www.coilcraft.com
MSS1038-683 68 0.213 1.5
NPIS64D330MTRF 33 0.124 1.1 NIC www.niccomp.com
The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times over the supply voltage and load current range.
AL8807
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Application Information (cont.)
The following equations can be used as a guide, with reference to Figure 1 - Operating waveforms.
Switch ‘On’ time Switch ‘Off’ time
RrR
x
IVV IL
tSWLSAVGLEDIN
ON
rR
x
IVV IL
tLSAVGDLED
OFF
Where:
L is the coil inductance (H)
rL is the coil resistance (Ω)RS is the current sense resistance (Ω)
Iavg is the required LED current (A)
ΔI is the coil peak-peak ripple current (A) {Internally set to 0.3 x Iavg}
VIN is the supply voltage (V)
VLED is the total LED forward voltage (V)
RSW is the switch resistance (Ω) {=0.5Ω nominal}
VD is the diode forward voltage at the required load current (V)
Thermal Considerations
For continuous conduction mode of operation, t he absolute maximum junction tempe rature must not b e exceede d. The maximum p o wer dissipation
depends on several factors: the thermal resistance of the IC package JA, 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) / JA
where
T
J(MAX) is the maximum operating junction temperature,
T
A is the ambient temperature, and
JA 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 AL8807’s
junction to ambient thermal resistance, JA and device power dissipation.
JA, is layout dependent and package dependent; the AL8807W5’s JA 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:
P
D(MAX) = (125°C − 25°C) / (250°C/W) = 0.4W for single-layer PCB
P
D(MAX) = (125°C − 25°C) / (160°C/W) = 0.625W for standard four-layer PCB
Figure 35, shows the power derating of the AL8807W5 on two (one single-layer and four-la yer) diffe rent 25x25mm PC B with 1oz copper standing in
still air and the AL8807MP on an FR4 51x51mm PCB with 2oz copper standing in still air.
Figure 35 Derating Curve for Different PCB
AL8807
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Application Information (cont.)
EMI and Layout Considerations
The AL8807 is a switching regulator with fast edges and measures small differential voltages; as a result of this care has to be taken with
decoupling and layout of the PCB.To help with these effects the AL8807 has been developed to minimise radiated emissions by controlling the
switching speeds of the internal power MOSFET. The rise and fall times are controlled to get the right compromise between power dissipation due
to switching losses and radiated EMI. The turn-on edge (falling edge) dominates the radiated EMI which is due to an interaction between the
Schottky diode (D1), Switching MOSFET and PCB tracks. After the Schottky diode reverse recovery time of around 5ns has occurred; the falling
edge of the SW pin sees a resonant loop between the Schottky diode capacitance and the track inductance, LTRACK, See figure 36.
Figure 36 PCB Loop Resonance
The tracks from the SW pin to the Anode of the Schottky diode, D1, and then from D1’s cathode to the decoupling capacitors C1 should be as short
as possible. There is an inductance internally in the AL8807 this can be assumed t o be around 1 nH. For PCB tracks a figure of 0.5nH per mm can
be used to estimate the primary resonant frequency. If the track is capable of handling 1A increasing the thickness will have a minor effect on the
inductance and length will dominate the size of the inductance. The resonant frequency of any oscillation is determined by the combined
inductance in the track and the effective capacitance of the Schottky diode. An example of good layout is shown in figure 37 - the stray track
inductance should be less than 5nH.
Figure 37 Recommended PCB La yout
AL8807
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Application Information (cont.)
Recommendations for minimising radiated EMI and other transients and thermal considerations are:
1. The decoupling capacitor (C1) has to be placed as close as possible to the VIN pin and D1 Cathode
2. The freewheeling diode’s (D1) anode, the SW pin and the inductor have to be placed as close as possible to each other to avoid ringing.
3. The Ground return path from C1 must be a low impedance path with the ground plane as large as possible
4. The LED current sense resistor (R1) has to be placed as close as possible to the VIN and SET pins.
5. The majority of the conducted heat from the AL88 07 is through the GND pin 2. A maximum eart h plane with thermal vias into a second earth
plane will minimise self-heating
6. To reduce emissions via long leads on the supply input and LEDs low RF impedance capacitors (C2 and C5 ) should be used at the point the
wires are joined to the PCB
A typical application for the AL8807 is an LED MR16 lamp (schematic shown in Figure 38).
Figure 38 MR16 Circuit Schematic
An evaluation board for the AL8807 (named the AL8807EV2) for MR16 is available on request from your local Diodes’ sales representative. This
board follows Diodes’ recommendations for low EMI. Images of the top layer and bottom layers are shown in Figure 39.
Figure 39 Recommended MR16 PCB Layout
AL8807
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Application Information (cont.)
The associated EMI measurements for this board using the AL8807 is shown in figure 40.
Figure 40 AL8807EV2 Radiated EMI Performance
The EMI performance was measured at 12VDC dri ving two white LEDs (VF = 3.1V at 660mA) on the AL8807EV2. The red bold line i s for EN55022
class B used for domestic equipment including lighting. The bottom magenta line is the noise floor of the test chamber. The middle purple line is the
EMI emitted radiation of the AL8807 over 30MHz to 1000MHz. This shows that the AL8807 passes the standard with at least 16dB margin.
MR16 lamps typically operate from 12VDC or 12VAC, using conventional electromagnetic transformers or electronic transformers.
In enclosed lamps such MR16 the ability for the device to operate at high ambient temperatures is critical and figure 41 shows the surface
temperature of the AL8807 on AL8807EV2 in operation under the same conditions as the EMI tests at an free air temperature of 25°C. It is
anticipated that the internal junction temperature is approximately 6°C hotter than the surface temperature.
Figure 41 Thermal picture of AL8807EV2 at 12VDC 2 white LEDS at 660mA
The thermal image shows that components increasing the board temperature are the inductor, Schottky diodes and the AL8807.
An inductor choice of 33µH with saturation current higher than 1.1A, will limit the frequency variation between 180kHz and 400k Hz 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 AL8807 guarantees high performance levels with both 12VAC and 12VDC power supplies.
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.
AL8807
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Ordering Information
Package Packing
W5 : SOT25
MP : MSOP-8EP 7 : 7” Tape & Reel
13 : 13” Tape & Reel
A
L8807 XX - X X
Part Number Status Package Code Packaging 7” Tape and Reel
Quantity Part Number Suffix
AL8807W5-7 New Product W5 SOT25 3000/Tape & Reel -7
AL8807MP-13 New Product MP MSOP-8EP 2500/Tape & Reel -13
Marking Information
(1) SOT25
1 2 3
5
7
4
XX YW X
(Top View)
XX : Identification code
W : Week : A~Z : 1~26 week;
X : A~Z : Internal code
Y : Year 0~9
a~z : 27~52 week; z represents
52 and 53 week
Part Number Package Identification Code
AL8807W5-7 SOT25 B6
(2) MSOP-8EP
Part Number Package
AL8807MP-13 MSOP-8EP
AL8807
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Package Outline Dimensions (All dimensions in mm.)
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.
(1) SOT25
(2) MSOP-8EP
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°
All Dimensions in mm
MSOP-8EP
Dim Min Max Typ
A - 1.10 -
A1 0.05 0.15 0.10
A2 0.75 0.95 0.86
A3 0.29 0.49 0.39
b 0.22 0.38 0.30
c 0.08 0.23 0.15
D 2.90 3.10 3.00
D1 1.60 2.00 1.80
E 4.70 5.10 4.90
E1 2.90 3.10 3.00
E2 1.30 1.70 1.50
E3 2.85 3.05 2.95
e - - 0.65
L 0.40 0.80 0.60
a 0° 8° 4°
x - - 0.750
y - - 0.750
All Dimensions in mm
A
M
JL
D
B C
H
KN
1
D
A
A1
A2
E
e
y
x
Seating Plane
Gauge Plane
L
D
8Xb
See Detail C
Deta il C
c
a
E1
E3
A3
E2
4X10°
4X10°
0.25
D1
AL8807
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Suggested Pad Layout
Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.
(1) SOT25
(2) MSOP-8EP
Dimensions Value (in mm)
Z 3.20
G 1.60
X 0.55
Y 0.80
C1 2.40
C2 0.95
Dimensions Value
(in mm)
C 0.650
G 0.450
X 0.450
X1 2.000
Y 1.350
Y1 1.700
Y2 5.300
X
Z
Y
C1
C2C2
G
G
X C
Y
Y2 Y1
X1
AL8807
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