AL8807Q
HIGH EFFICIENCY LOW 30V 1.3A
AUTOMOTIVE GRADE BUCK LED DRIVER
Description
Pin Assignments
The AL8807Q is a step-down DC/DC converter designed to drive
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
(Top View)
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 AL8807Q switches at frequency up
SET
VIN
to 1MHz with controlled rise and fall times to reduce EMI. This allows
GND
N/C
GND
SW
CTRL
SW
the use of small size external components, hence minimizing the PCB
area needed.
Maximum output current of AL8807Q is set via an external resistor
connected between the VIN and SET input pins. Dimming is achieved
MSOP-8EP
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.
The AL8807Q has been qualified to AEC-Q100 Grade 1 and is
Automotive Grade supporting PPAPs
Applications
Features
LED driving current up to 1.3A
Automotive Interior LED Lamps
Better than 5% accuracy
Automotive Exterior LED Lamps
High efficiency up to 96%
Optimally controlled switching speeds
Operating input voltage from 6V to 30V
PWM/DC input for dimming control
Built-in output open-circuit protection
Automotive Grade with AEC-Q100 Qualification
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)
Automotive Grade
Qualified to AEC-Q100 Standards for High Reliability
PPAP Capable (Note 4)
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 those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
4. Automotive products are AEC-Q100 qualified and are PPAP capable. Automotive, AEC-Q100 and standard products are electrically and thermally the same,
except where specified. For more information, please refer to http://www.diodes.com/quality/product_compliance_definitions/.
Typical Applications Circuit
AL8807Q
Document number: DS36904 Rev. 1 - 2
1 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
Pin Descriptions
Pin Name
SET
GND
Pin Number
1
2, 3
CTRL
4
SW
5, 6
N/C
7
VIN
8
EP
EP
Functions
Set Nominal Output Current Pin. Configure the output current of the device.
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.
Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI.
no connection
Input Supply Pin. Must be locally decoupled to GND with > 2.2µF X7R ceramic capacitor – see applications
section for more information.
Exposed pad/TAB connect to GND and thermal mass for enhanced thermal impedance. Should not be used as
electrical ground conduction path.
Functional Block Diagram
Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.)
Symbol
ESD HBM
ESD MM
ESD CDM
Parameter
Human Body Model ESD Protection
Machine Model ESD Protection
Charged Device Model ESD Protection
Ratings
4000
300
1000
Unit
V
V
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
CTRL pin input voltage
-0.3 to +6
V
VCTRL
ISW-RMS
ISW-PK
DC or RMS Switch current
1.6
A
Peak Switch current (<10%)
2.5
A
+150
°C
Junction Temperature
TJ
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.
AL8807Q
Document number: DS36904 Rev. 1 - 2
2 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Symbol
Min
Max
Operating Input Voltage relative to GND
6.0
30
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
VIN
Parameter
Unit
Voltage Low for PWM dimming relative to GND
0
0.4
V
fSW
Maximum switching frequency
—
1
MHz
ISW
Continuous switch current
—
1.3
A
TJ
Junction Temperature Range
-40
125
°C
VCTRLL
Electrical Characteristics (@ VIN = 12V, TA = +25°C, unless otherwise specified.)
Symbol
VINSU
VINSH
Parameter
Internal regulator start up threshold
Min
Typ
Max
Unit
VIN rising
Conditions
—
—
5.9
V
100
—
300
mV
—
—
350
µA
Internal regulator hysteresis threshold
VIN falling
IQ
Quiescent current
Output not switching (Note 5)
IS
Input supply Current
CTRL pin floating f = 250kHz
—
1.8
5
mA
Set current Threshold Voltage
—
95
100
105
mV
VTH
VTH-H
Set threshold hysteresis
—
—
±20
—
mV
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
On Resistance of SW MOSFET
ISW = 1A
—
0.25
0.4
Ω
tR
SW rise time
12
—
ns
SW fall time
VSENSE = 100±20mV, fSW = 250kHz
VSW = 0.1V~12V~0.1V CL = 15pF
—
tF
—
20
—
ns
Switch leakage current
VIN =30V
—
—
0.5
μA
JA
Thermal Resistance Junction-toAmbient (Note 6)
(Note 7)
—
69
—
C/W
JC
Thermal Resistance Junction-to-case
(Note 8)
(Note 7)
—
4.3
—
—
ISET
RDS(on)
ISW_Leakage
Notes:
5. AL8807Q 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
6. Refer to figure 35 for the device derating curve.
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 exposed pad.
AL8807Q
Document number: DS36904 Rev. 1 - 2
3 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
Typical Performance Characteristics (@TA = +25°C, unless otherwise specified.)
900
400
V CTRL = 0V
V SET = V IN
350
TA = 25 °C
700
FREQUENCY (kHz)
300
IIN (µA)
250
200
150
500
L = 68µH
400
300
L = 100µH
100
50
0
0
5
10
15
20
25
30
VI N (V)
Supply Current (not switching) vs. Input Current
100
80
90
60
70
40
ICTRL (µA)
LED CURRENT (A)
600
200
100
0
VIN = 12V
1 LED
RSET = 150m
TA = 25°C
L = 33µH
800
60
40
0
1
2
3
4
5
VCTRL
Figure 2. Switching Frequency vs. VCTRL
VSET = VIN = 12V
TA = 25°C
20
0
30
-20
20
-40
-60
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.0
VCTRL (V)
Figure 4. ICTRL vs. VCTRL
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
CTRL PIN VOLTAGE (V)
Figure 3. LED Current vs. VCTRL
2.52
3
VCTRL = Open
VSET = VIN = 12V
2.5
2.51
VCTRL (V)
V CTRL (V)
2
1.5
1
V CTRL = Open
2.49
V SET = V IN
TA = 25 C
0.5
0
2.50
0
5
10
15
20
VIN (V)
V CTRL vs. Input Voltage
(CTRL pin open circuit)
AL8807Q
Document number: DS36904 Rev. 1 - 2
25
2.48
-40
30
4 of 16
www.diodes.com
-15
10
35
60
85
110
AMBIENT TEMPERATURE (°C)
Figure 6. VCTRL VS. TEMPERATURE
March 2014
© Diodes Incorporated
AL8807Q
Typical Performance Characteristics (cont.) (@TA = +25°C, unless otherwise specified.)
7
160
0.5
LED Current
Error
5
LED Current
4
180
0.7
0.6
6
200
0.4
0.3
3
140
RDS(ON) (m)
8
LED CURRENT ERROR (%)
0.8
L = 68H, RS = 150m
TA = 25C, VIN = 12V
CTRL = PWM, fPWM = 500Hz
1 LED
LED CURRENT (A)
9
100
80
60
0.2
2
120
40
0.1
1
0
0
20
40
60
80
PWM DUTY CYCLE
Figure 7. ILED vs. PWM Duty Cycle
VCTRL = Open
VSET = VIN 12V
20
0
100
0
TA = 25C
0
5
10
15
20
25
VIN (V)
RDS(ON) vs. Input Voltage
100
400
90
350
80
DUTY CYCLE (%)
RDS(ON) (m)
30
300
250
200
VCTRL = Open
VSET = VIN = 12V
150
3 LEDS
L = 68µH
RS = 100m
TA = 25°C
VCTRL = Open
70
60
2 LEDS
50
40
30
20
10
100
-40
-15
10
35
60
85
110
Ambient Temperature (C)
Figure 9. SW RDS(ON) vs. Temperature
Figure 11 SW Output Rise Time
AL8807Q
Document number: DS36904 Rev. 1 - 2
0
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 10. Duty Cycle vs. Input Voltage
Figure 12 SW Output Fall Time
5 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
Typical Performance Characteristics 670mA LED Current (cont.) (@TA = +25°C, unless otherwise specified.)
10
350
SWITCHING FREQUENCY (kHz)
LED CURRENT ERROR (%)
8
6
4
2
0
-2
-4
-6
-8
-10
9
200
150
100
50
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 14. Switching Frequency vs. Input Voltage
500
8
450
SWITCHING FREQUENCY (kHz)
10
6
4
2
0
-2
-4
-6
-8
-10
6
9
300
250
200
150
100
50
6
9
6
SWITCHING FREQUENCY (kHz)
800
L = 33µH
RS = 150m
TA = 25°C
VCTRL = Open
8
1 LED
2 LEDs
2
0
-2
3 LEDs
4 LEDs
5 LEDs
6 LEDs
-4
7 LEDs
-6
8 LEDs
-8
-10
350
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 16. Switching Frequency vs. Input Voltage
10
4
9
400
0
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 15. LED Current Deviation vs. Input Voltage
LED CURRENT ERROR (%)
250
0
6
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 13. LED Current Deviation vs. Input Voltage
LED CURRENT ERROR (%)
6
300
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 17. LED Current Deviation vs. Input Voltage
AL8807Q
Document number: DS36904 Rev. 1 - 2
6 of 16
www.diodes.com
L = 33µH
RS = 150m
TA = 25°C
VCTRL = Open
700
600
500
400
300
1 LED
200
7 LEDs
100
0
8 LEDs
5 LEDs
3 LEDs
4 LEDs
6 LEDs
2 LEDs
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 18. Switching Frequency vs. Input Voltage
March 2014
© Diodes Incorporated
AL8807Q
Typical Performance Characteristics 1A LED Current (cont.) (@TA = +25°C, unless otherwise specified.)
350
10
SWITCHING FREQUENCY (kHz)
LED CURRENT ERROR (%)
8
6
4
2
0
-2
-4
-6
-8
-10
6
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 19. LED Current Deviation vs. Input Voltage
SWITCHING FREQUENCY (kHz)
8
LED CURRENT ERROR (%)
250
200
150
1 LED
100
50
4 LEDs 5 LEDs 6 LEDs
2 LEDs3 LEDs
6
9
0
6
9
7 LEDs
8 LEDs
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 20. Switching Frequency vs. Input Voltage
350
10
6
4
2
0
-2
-4
-6
-8
-10
300
0
9
L = 100µH
RS = 100m
TA = 25°C
VCTRL = Open
6
300
250
200
150
100
50
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 22. Switching Frequency vs. Input Voltage
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 21. LED Current Deviation vs. Input Voltage
600
10
SWITCHING FREQUENCY (kHz)
LED CURRENT ERROR (%)
8
6
4
2
0
-2
-4
-6
-8
-10
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 23. LED Current Deviation vs. Input Voltage
AL8807Q
Document number: DS36904 Rev. 1 - 2
7 of 16
www.diodes.com
500
400
300
200
100
0
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 24. Switching Frequency vs. Input Voltage
March 2014
© Diodes Incorporated
AL8807Q
Typical Performance Characteristics 1.3A LED Current (cont.) (@TA = +25°C, unless otherwise specified.)
10
250
L = 100µH
RS = 77m
TA = 25°C
VCTRL = Open
SWITCHING FREQUENCY (kHz)
LED CURRENT ERROR (%)
8
6
4
2
0
-2
-4
-6
-8
-10
6
200
150
100
1 LED
50
0
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 25. LED Current Deviation vs. Input Voltage
2 LEDs 3 LEDs
5 LEDs 6 LEDs7 LEDs 8 LEDs
4 LEDs
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 26. Switching Frequency vs. Input Voltage
300
10
L = 68µH
RS = 77m
T A = 25°C
VCTRL = Open
SWITCHING FREQUENCY (kHz)
LED CURRENT ERROR (%)
8
6
4
2
0
-2
-4
-6
-8
-10
250
200
150
100
1 LED
50
2 LEDs 3 LEDs 4 LEDs
6 LEDs
5 LEDs
6
0
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 27. LED Current Deviation vs. Input Voltage
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 28. Switching Frequency vs. Input Voltage
10
SWITCHING FREQUENCY (kHz)
LED CURRENT ERROR (%)
9
600
L = 33µH
RS = 77m
TA = 25°C
VCTRL = Open
8
6
4
2
0
-2
-4
-6
-8
-10
7 LEDs 8 LEDs
6
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 29. LED Current Deviation vs. Input Voltage
AL8807Q
Document number: DS36904 Rev. 1 - 2
8 of 16
www.diodes.com
500
400
300
200
1 LED
100
0
4 LEDs
2 LEDs 3 LEDs
6
5 LEDs
6 LEDs
7 LEDs
8 LEDs
9
12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 30. Switching Frequency vs. Input Voltage
March 2014
© Diodes Incorporated
AL8807Q
Application Information
The AL8807Q is a hysteretic (also known as equal ripple) LED driver with integrated power switch. It is available in two packages that provide a
PCB area-power dissipation capability compromise. It is recommended that at higher LED currents/smaller PCBs that the MSOP-8EP version is
used to maximize the allowable LED current over a wider ambient temperature range.
AL8807Q Operation
In normal operation, when voltage is applied at +VIN, the AL8807Q 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 AL8807Q 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 AL8807Q. 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:
ILED
VTHD
R1
For example for a desired LED current of 660mA and a default voltage VCTRL=2.5V the resulting resistor is:
R1
VTHD
0.1
150m
ILED
0.66
Analog 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:
ILED
VCTRL VTHD
VREF R SET
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
V
be clamped to approximately 100% and follows ILED THD .
RSET
When the CTRL voltage falls below the threshold, 0.4V, the output switch is turned off which allows PWM dimming.
AL8807Q
Document number: DS36904 Rev. 1 - 2
9 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
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%
PWM dimming [%]
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 AL8807Q. 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.
AL8807Q
Document number: DS36904 Rev. 1 - 2
10 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
Application Information (cont.)
Soft Start
The AL8807Q 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 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 AL8807Q 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 AL8807Q; however a 4.7μF input capacitor is suggested for input voltages
approaching 30V.
AL8807Q
Document number: DS36904 Rev. 1 - 2
11 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
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 AL8807Q applications.
Inductor Selection
Recommended inductor values for the AL8807Q 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 AL8807Q are listed in the table below:
L
DCR
ISAT
Part No.
(µH)
(V)
(A)
MSS1038-333
33
0.093
2.3
MSS1038-683
68
0.213
1.5
NPIS64D330MTRF
33
0.124
1.1
Manufacturer
CoilCraft www.coilcraft.com
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.
AL8807Q
Document number: DS36904 Rev. 1 - 2
12 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
Application Information (cont.)
Inductor Selection (cont.)
The following equations can be used as a guide, with reference to Figure 1 - Operating waveforms.
Switch ‘On’ time
L I
tON
VIN VLED IAVG x RS rL RSW
Switch ‘Off’ time
tOFF
LI
VLED VD IAVG x RS rL
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)
∆I 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, the absolute maximum junction temperature must not be exceeded. The maximum power 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
TJ(MAX) is the maximum operating junction temperature,
TA 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 AL8807Q’s
junction to ambient thermal resistance, JA and device power dissipation. To support high LED drive at higher ambient temperatures the AL8807Q
has been packaged in thermally enhanced MSOP-8EP package.
JA, is layout dependent and the AL8806Q’s JA in MSOP-8EP on a
1600
approximately 69°C/W.
Therefore the maximum power dissipation at TA = 25°C is:
PD(MAX )
125 C 25C 1.45 W
69 C / W
Figure 35, shows the power derating of the AL8807QMP on an FR4
51x51mm PCB with 2oz copper standing in still air.
Power dissipation (mW)
51 x 51mm double layer PCB with 2oz copper standing in still air is
1400
1200
1000
800
600
400
200
0
As the ambient temperature increases and/or the PCB area reduces
the maximum allowable power dissipated by the AL8807Q will
decrease.
AL8807Q
Document number: DS36904 Rev. 1 - 2
MSOP-8EP
13 of 16
www.diodes.com
-40 -25 -10
5 20 35 50 65 80
Ambient temperature (°C)
95 110 125
Figure 35 Derating Curve for Different PCB
March 2014
© Diodes Incorporated
AL8807Q
Application Information (cont.)
EMI and Layout Considerations
The AL8807Q 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 AL8807Q 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 AL8807Q this can be assumed to be around 1nH. 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.
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.
4.
The Ground return path from C1 must be a low impedance path with the ground plane as large as possible
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 AL8807Q is through the GND pin 2. A maximum earth 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.
AL8807Q
Document number: DS36904 Rev. 1 - 2
14 of 16
www.diodes.com
March 2014
© Diodes Incorporated
AL8807Q
Ordering Information
Part Number
Package Code
Packaging
(Note 9)
AL8807QMP-13
MP
MSOP-8EP
Note:
Packing: 13” Tape and Reel
Quantity
2500
Tape Width
12mm
Part Number Suffix
-13
Qualification Grade
(Note 10)
Automotive Grade
9. 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
10. AL8807Q has been qualified to AEC-Q100 grade 1 and is classified as “Automotive Grade” which supports PPAP documentation.
See AL8807 datasheet for commercial qualified versions.
Marking Information
(1)
MSOP-8EP
Part Number
AL8807QMP-13
Package
MSOP-8EP
Package Outline Dimensions (All dimensions in mm.)
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.
D
1
D
4X
x
5
2
.
0
10
°
2
E
E
e
n
a
l
P
e
g
u
a
G
e
n
a
l
P
g
n
i
t
a
e
S
y
a
L
10
°
3
E
C
l
i
a
t
e
D
b
X
8
e
1
4X
c
3
A
1
A
2
A
A
1
E
D
C
l
i
a
t
e
D
e
e
S
AL8807Q
Document number: DS36904 Rev. 1 - 2
15 of 16
www.diodes.com
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
March 2014
© Diodes Incorporated
AL8807Q
Suggested Pad Layout
Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.
X
C
G
Y2
Y
Dimensions
Y1
C
G
X
X1
Y
Y1
Y2
X1
Value
(in mm)
0.650
0.450
0.450
2.000
1.350
1.700
5.300
IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS 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).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume
all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated
website, harmless against all damages.
Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel.
Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and
hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or
indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.
Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings
noted herein may also be covered by one or more United States, international or foreign trademarks.
This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the
final and determinative format released by Diodes Incorporated.
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 products and any
use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
information or support that may be provided by Diodes Incorporated. Further, 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 © 2014, Diodes Incorporated
www.diodes.com
AL8807Q
Document number: DS36904 Rev. 1 - 2
16 of 16
www.diodes.com
March 2014
© Diodes Incorporated