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P
L8807B
Description
The AL8807B 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
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 AL8807B 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 AL8807B is set via an external resistor
connected between the V
achieved by applying 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.
and SET input pins. Dimming is
IN
NEW PRODUCT
Features
LED driving current up to 1.3A
Better than 5% accuracy
High efficiency up to 96%
Optimally controlled switching speeds
Operating input voltage from 6V to 36V
PWM input for dimming control
Open-Circuit LED protection
LED Chain Short Circuited
Over-Temperature Protection
MSOP-8EP Available in “Green” Molding Compound (No Br,
Sb) with lead Free Finish/ RoHS Compliant
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Pin Assignments
SET
GND
GND
CTRL
Applications
MR16 lamps
General illumination lamps
12V powered LED Lamps
24V powered LED Lamps
(Top View)
V
N/C
SW
SW
MSOP-8E
HIGH EFFICIENCY 36V 1.3A PWM DIMMABLE BUCK LED DRIVER
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.
Typical Application Circuit
IN
AL88070B
Document number: DS36191 Rev. 1 - 2
PWM Dimming
Input:
VIN:
6 ~ 36V
D1
C1
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R1
IN
V
AL8807B
GND
CTRL
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SETSW
L1
C2
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© Diodes Incorporated
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Pin Descriptions
L8807B
Pin Name
SET 1 Set Nominal Output Current Pin. Configure the output current of the device.
GND 2, 3 GND Pins
CTRL 4
SW 5, 6 Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI.
N/C 7 no connection
V
IN
EP EP
Pin
Number
8
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Functional Block Diagram
Function
Dimming and On/Off Control Input.
Leave floating for normal operation.
(V
= V
CTRL
Drive to voltage below 0.4V to turn off output current
A PWM signal ( 2.5V) allows the output current to be adjusted below the level set by the resistor
connected to SET input pin.
Input Supply Pin. Must be locally decoupled to GND with > 2.2µF X7R ceramic capacitor – see
applications section for more information.
Exposed pad/TAB connects to GND and thermal mass for enhanced thermal impedance. Should not be
used as electrical ground conduction path.
= 2.5V giving nominal average output current I
REF
= 0.1/RS)
OUTnom
AL88070B
Document number: DS36191 Rev. 1 - 2
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Absolute Maximum Ratings
Symbol Parameter Ratings Unit
ESD HBM Human Body Model ESD Protection 2.5 kV
ESD MM Machine Model ESD Protection 200 V
V
IN
V
SW
V
CTRL
I
SW-RMS
I
SW-PK
T
J
T
LEAD
T
ST
Caution: Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only;
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Recommended Operating Conditions
Continuous VIN Pin Voltage Relative to GND
SW Voltage Relative to GND -0.3 to +40 V
CTRL Pin Input Voltage -0.3 to +6 V
DC or RMS Switch Current MSOP-8EP 1.6 A
Peak Switch Current (<10%) 2.5 A
Junction Temperature +150 °C
Lead Temperature Soldering +300 °C
Storage Temperature Range -65 to +150 °C
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.
-0.3 to +40 V
L8807B
Symbol Parameter Min Max Unit
V
IN
V
CTRLH
V
CTRLL
f
SW
I
SW
T
J
Electrical Characteristics (V
Symbol Parameter Conditions Min Typ Max Unit
V
INSU
V
INSH
IQ
IS
VTH
V
TH-H
I
SET
R
CTRL
V
REF
R
DS(ON)
tR
tF
T
OTP
T
OTP-Hyst
I
SW_Leakage
JA
JC
Notes: 4. AL8807B does not have a low power standby mode but current consumption is reduced when output switch is inhibited: V
tested with V
5. Refer to figure 39 for the device derating curve.
6. 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.
7. Dominant conduction path is via exposed pad.
Operating Input Voltage Relative to GND 6.0 36 V
Voltage High for PWM Dimming Relative to GND 2.5 5.5 V
Voltage Low for PWM Dimming Relative to GND 0 0.4 V
Maximum Switching Frequency — 1 MHz
Continuous Switch Current MSOP-8EP — 1.3 A
Junction Temperature Range -40 +125 °C
= 12V, @TA = +25°C, unless otherwise specified.)
IN
Internal Regulator Start Up Threshold
Internal Regulator Hysteresis Threshold
Quiescent Current Output not switching (Note 4) — — 350 µA
Input Supply Current CTRL pin floating f = 250kHz — 1.8 5 mA
Set Current Threshold Voltage
Set Threshold Hysteresis
SET Pin Input Current
CTRL Pin Input Resistance Referred to internal reference — 50 — k
Internal Reference Voltage
On Resistance of SW MOSFET
SW Rise Time
SW Fall Time — 20 — ns
Over-Temperature Shutdown
Over-Temperature Hysteresis
Switch Leakage Current
Thermal Resistance Junction-toAmbient (Note 5)
Thermal Resistance Junction-to-case
(Note 7)
2.5V.
CTRL
VIN rising
VIN falling
—
—
V
= VIN-0.1
SET
ISW = 1A
V
= 100 ±20mV fSW = 250kHz
SENSE
VSW = 0.1V~12V~0.1V CL = 15pF
—
—
VIN =36V
(Note 6) — 69 — °C/W
(Note 6) — 4.3 — —
— — 5.9 V
100 — 300 mV
95 100 105 mV
— ±15 — mV
— 16 22 µA
— 2.5 — V
— 0.25 0.4
— 12 — ns
— 155 — °C
— 55 — °C
— — 0.5 A
= 0V. Parameter is
SENSE
AL88070B
Document number: DS36191 Rev. 1 - 2
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A
(°C)
R
p
R
Typical Performance Characteristics (@T
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400
350
300
250
200
IN
I (µA)
150
100
50
0
0 3 6 9 15 18 21 24 27 30 33
12 36
V (V)
IN
Figure 1. Supply Current (not switching) vs.
Input Voltage
3
2.5
2
V = 0V
CTRL
V = V
SET IN
T = 25°C
A
= +25°C, unless otherwise specified.)
A
80
V = V = 12V
SET IN
60
T = 25°C
A
40
)
20
CTRL
0
I (µ
-20
-40
-60
0.0 0.5 1.0 1.5 2.5 3.0 3.5 4.0 4.5 5.0
2.0 5.0
V (V)
Figure 2 I
2.52
2.51
CTRL
CTRL
vs. V
CTRL
V = Open
CTRL
V = V= 12V
SET IN
L8807B
1.5
CTRL
V (V)
2.50
CTRL
V (V)
1
V = Open
CTRL
0.5
0
0 3 6 9 12 18 21 24 27 30 36
Figure 3 V
15 33
V (V)
IN
vs. Input Voltage
CTRL
(CTRL Pin open circuit)
V = V
SET IN
T = 25°C
A
300
2.49
2.48
-40 -15 10 35 60 85 110
AMBIENT TEMPERATURE
Figure 4 V
vs. Temperature
CTRL
400
270
240
210
180
(m )
150
DS(ON)
120
90
60
30
0
6 9 12 18 21 24 27 30 36
15 33
Figure 5 SW R
V (V)
IN
vs. Input Voltage
DS(ON)
V = Open
CTRL
V = V
SET IN
T = 25°C
A
350
300
(m )
250
DS(ON)
200
150
100
-40 -15 35 60 11010 85
Ambient Tem
Figure 6 SW R
eratur e (C)
vs. Temperature
DS(ON)
V = Open
CTRL
V = V= 12V
SET IN
AL88070B
Document number: DS36191 Rev. 1 - 2
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Typical Performance Characteristics
(cont.) (@TA = +25°C, unless otherwise specified.)
L8807B
NEW PRODUCT
Figure 7 I
Figure 9. Efficiency vs. Input Voltage
vs. PWM Duty Cycle
LED
Figure 8. Duty Cycle vs. Input Voltage
Figure 10. On-time vs. Input Voltage
Figure. 11 SW Output Rise Time Figure. 12 SW Output Fall Time
AL88070B
Document number: DS36191 Rev. 1 - 2
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Typical Performance Characteristics
(670mA LED current) (@TA = +25°C, unless otherwise specified.)
L8807B
NEW PRODUCT
Figure 13. LED Current Deviation vs. Input Voltage
Figure 15. LED Current Deviation vs. Input Voltage
Figure 14. Switching Frequency vs. Input Voltage
Figure 16. Switching Frequency vs. Input Voltage
AL88070B
Document number: DS36191 Rev. 1 - 2
Figure 17. LED Current Deviation vs. Input Voltage
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Figure 18. Switching Frequency vs. Input Voltage
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March 2014
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Typical Performance Characteristics
(1A LED currentMSOP-8EP) (@TA = +25°C, unless otherwise specified.)
L8807B
NEW PRODUCT
Figure 19. LED Current Deviation vs. Input Voltage
Figure 21. LED Current Deviation vs. Input Voltage
Figure 20. Switching Frequency vs. Input Voltage
Figure 22. Switching Frequency vs. Input Voltage
AL88070B
Document number: DS36191 Rev. 1 - 2
Figure 23. LED Current Deviation vs. Input Voltage
Figure 24. Switching Frequency vs. Input Voltage
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Typical Performance Characteristics
L8807B
(1.3A LED current MSOP-8EP) (@TA = +25°C, unless otherwise specified.)
NEW PRODUCT
Figure 25. LED Current Deviation vs. Input Voltage
Figure 27. LED Current Deviation vs. Input Voltage
Figure 26. Switching Frequency vs. Input Voltage
Figure 28. Switching Frequency vs. Input Voltage
AL88070B
Document number: DS36191 Rev. 1 - 2
Figure 29. LED Current Deviation vs. Input Voltage
Figure 30. Switching Frequency vs. Input Voltage
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Application Information
The AL8807B 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.
AL8807B Operation
In normal operation, when voltage is applied at +VIN, the AL8807B 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 R
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 R
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 R
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 R
NEW PRODUCT
LED Current Control
The LED current is controlled by the resistor R1 in Figure 31.
. The internal circuit of the AL8807B senses the voltage across R1 and applies a
1
, which is sensed by the AL8807B. A voltage proportional to the sense voltage across R1 is
1
.
1
L8807B
1
, L1,
R1
D1
VIN:
6 ~ 36V
C1
PWM Dimming
Input:
Figure 31 Typical Application Circuit
Connected between V
I
LED
For example for a desired LED current of 660mA and a default voltage V
1R
and SET the nominal average output current in the LED(s) is defined as:
IN
V
THD
1R
V
THD
I
LED
1.0
66.0
AL88070B
Document number: DS36191 Rev. 1 - 2
IN
V
AL8807B
GND
CTRL
m150
SETSW
C2
L1
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Ch4: LED Current
VIN= 12V
=25ºC
T
A
2 LEDs
20ns/div
No C2
Ch2: 2V/div
Ch4: 100mA/div
Ch2: SW Pin
Figure 32 Typical Operating Waveform (C2 not fitted)
=2.5V the resulting resistor is:
CTRL
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L8807B
Applications 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 R
SET
NEW PRODUCT
While the PWM pin is high, the AL8807B switches as normal. When the PWM pin is brought low the output switch is turned off causing the SW pin
to go high (one Schottky voltage drop above V
to zero. The time taken for the inductor current is dependent on the LED current, inductor value and LED chain voltage.
As the duty cycle gets smaller or PWM dimming frequency increases then fewer normal hysteretic switching cycles occur which will affect the
overall average LED current.
Figure 33 PWM Dimming waveforms (f
). It remains high (one Schottky voltage drop above VIN) until the current through the inductor falls
IN
= 500Hz, 25% Duty Cycle f
PWM
SW(N OM)
= 530kHz)
.
To achieve high resolution the PWM frequency has to be much lower than the nominal switching frequency and the LED current output filter
capacitor across the LEDs must not be used. The figures above have an LED current output filter present.
AL88070B
Document number: DS36191 Rev. 1 - 2
Figure 34 PWM Dimming waveforms (f
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= 500Hz, 2% Duty Cycle f
PWM
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SW(N OM)
= 530kHz)
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L8807B
Applications Information
Figures 35 and 36 show the PWM dimming performance of the AL8807B with a range of PWM frequencies with a nominal switching frequency of
530kHz.
(cont.)
NEW PRODUCT
Looking at difference between duty cycle and percentage of full scale LED current yields a “Linearity Error”:
The accuracy of the PWM dimming is affected by both the PWM frequency and also the switching frequency of the AL8807B. 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.
Figure 35 PWM Dimming at 530kHz nominal switching frequency
Figure 36 PWM Dimming Non-Linearity at 530kHz nominal switching frequency
AL88070B
Document number: DS36191 Rev. 1 - 2
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Applications Information
(cont.)
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 1F 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 AL8807B 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 2.2F input capacitor is sufficient for most intended applications of AL8807B; however a 4.7F input capacitor is suggested for input voltages
approaching 36V.
Diode Selection
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode with low reverse leakage at the
NEW PRODUCT
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 AL8807B applications.
Inductor Selection
Recommended inductor values for the AL8807B are in the range 33H to 100H.
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).
L8807B
The inductor should be mounted as close to the device as possible with low resistance/stray inductance connections to the SW pin.
AL88070B
Document number: DS36191 Rev. 1 - 2
Figure 37 Inductor value with input voltage and number of LEDs
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Applications Information (cont.)
Inductor Selection (cont.)
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 AL8807B are listed in the table below:
Part No.
L
(µH)
MSS1038-333 33 0.093 2.3
MSS1038-683 68 0.213 1.5
DCR
(V)
I
SAT
(A)
Manufacturer
CoilCraft www.coilcraft.com
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.
The following equations can be used as a guide, with reference to Figure 38 – typical switching waveforms.
Switch ‘On’ time
t
ON
NEW PRODUCT
Switch ‘Off’ time
Where:
L is the coil inductance (H)
r
R
I
I is the coil peak-peak ripple current (A)
{Internally set to 0.3 x Iavg}
V
V
R
V
t
OFF
is the coil resistance ()
L
is the current sense resistance ()
S
is the required LED current (A)
avg
is the supply voltage (V)
IN
is the total LED forward voltage (V)
LED
is the switch resistance () {=0.5 nominal}
SW
is the diode forward voltage at the required load current (V)
D
IL
x
IVV
IL
x
IVV
RrR
SWLSAVGLEDIN
rR
LSAVGDLED
Figure 38 Typical Switching Waveform
Off
VIN= 12V
T
=25ºC
A
2 LEDs
20ns/div
SW Pin: 2V/div
On
Thermal Protection
The AL8807B includes Over-Temperature Protection (OTP) circuitry that will turn off the device if its junction temperature gets too high. This is to
protect the device from excessive heat damage. The OTP circuitry includes thermal hysteresis that will cause the device to restart normal
operation once its junction temperature has cooled down by approximately 55°C.
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
between junction and ambient temperature.
The maximum power dissipation can be calculated using the following formula:
where
P
= (T
D(MAX)
is the maximum operating junction temperature Maximum recommended = 125°C
T
J(MAX)
is the ambient temperature, and
T
A
is the junction to ambient thermal resistance.
JA
J(MAX)
TA) /
JA
, is layout dependent and package dependent; the AL8807BMP’s JA on an FR4 51x51mm PCB with 2oz copper standing in still air is
JA
approximately 69°C/W.
So the maximum power dissipation at T
= (125°C 25°C) / (69°C/W) = 1.41W for the above dimensioned PCB
P
D(MAX)
= +25°C is:
A
AL88070B
Document number: DS36191 Rev. 1 - 2
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, PCB layout, airflow surrounding the IC, and difference
JA
© Diodes Incorporated
L8807B
March 2014
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L8807B
Applications Information
Figure 39, shows the power derating of the AL8807BMP on an FR4 51x51mm PCB with 2oz copper standing in still air. Changing the PCB
dimensions, material, amount of metal associated with the thermal and other PCB components will change the AL8807BMP’s junction-ambient
thermal impedance.
NEW PRODUCT
(cont.)
1600
1400
1200
1000
800
600
400
Power dissipation (mW)
200
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Figure 39 Derating Curve for Different PCB
MSOP-8EP
Ambient temperature (°C)
Soft-Start
The AL8807B does not have in-built soft-start action; this can be seen in Figure 40.
Figure 40 LED Current Start-up (V
At power–up V
Out turn-on threshold at around 5.6V. This causes the CTRL pin voltage to rise and reaches 2.5V – 100% LED current - before the AL8807B
fully turns on. When the AL8807B turns on, its output switch turns on causing the inductor current to increase until it reaches the upper threshold
of the sense current level and the switching process begins.
As the CTRL pin only has PWM functionality, placing a capacitor on the CTRL pin will have no effect on the ramp-up of the LED current; the
capacitor will just delay the ramp-up of the LED current and delay/extend the ramp-down of the LED current.
If some form of extra soft-start is required then the AL8807, AL8807A or PAM2861 should be considered.
AL88070B
Document number: DS36191 Rev. 1 - 2
rises exponentially, due to the bulk capacitor, the internal reference will reach 2.5V before VIN reaches the Under-Voltage Lock-
IN
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IN
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= 12V, I
= 667mA, 2 LEDs)
LED
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L8807B
Applications Information (cont.)
EMI and Layout Considerations
The AL8807B 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 AL8807B 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, L
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 AL8807B 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.
An example of good layout is shown in Figure 42 (showing SOT25 package) - the stray track inductance should be less than 5nH.
, See Figure 41.
TRACK
NEW PRODUCT
D1
C
D1
L
TRAC K
~5nH
SW
C
1
100nF
AL8807B
GND
Figure 41 PCB Loop Resonance
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 V
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 V
5. The majority of the conducted heat from the AL8807B 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
AL88070B
Document number: DS36191 Rev. 1 - 2
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Figure 42 Recommended PCB Layout
pin and D1 Cathode
IN
and SET pins.
IN
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L8807B
Applications Information
(cont.)
Fault Condition Operation
Open Circuit LEDs
The AL8807B has by default open LED protection. If the LEDs should become open circuit the AL8807B will stop oscillating; the SET pin will rise
to VIN and the SW pin will then fall to GND. No excessive voltages will be seen by the AL8807B.
LED Chain Shorted Together
If the LED chain should become shorted together (the anode of the top LED becomes shorted to the cathode of the bottom LED) the AL8807B will
continue to switch and the current through the AL8807B’s internal switch will still be at the expected current - so no excessive heat will be
generated within the AL8807B. However, the duty cycle at which it operates will change dramatically and the switching frequency will most likely
decrease. See Figure 43 for an example of this behavior at 24V input voltage driving 3 LEDs.
The on-time of the internal power MOSFET switch is significantly reduced because almost all of the input voltage is now developed across the
inductor. The off-time is significantly increased because the reverse voltage across the inductor is now just the Schottky diode voltage (See Figure
43) causing a much slower decay in inductor current.
NEW PRODUCT
Figure 43 Switching Characteristics (normal operation to LED chain shorted out)
High Temperature Operation and Protection
The AL8807B is a high efficiency switching LED driver capable of operating junction temperatures up to +125°C. This allows it operate with
ambient temperature in excess of +100°C given the correct thermal impedance to free air. If a fault should occur that leads to increased ambient
temperatures and hence junction temperature then the Over-Temperature Protection (OTP) of the AL8807B will cut-in, turning the output of the
AL8807B off. This will allow the junction temperature of the AL8807B to cool down and potentially giving an opportunity for the fault to clear itself.
The OTP shutdown junction temperature of the AL8807B is approximately +155°C with a hysteresis of +55°C. This means that the AL8807B will
never switch-off with a junction temperature below +125°C allowing the designer to design the system thermally to fully utilize the wide operating
junction temperature of the AL8807B.
AL88070B
Document number: DS36191 Rev. 1 - 2
www.diodes.com
16 of 18
March 2014
© Diodes Incorporated
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Ordering Information
L8807B
Part Number Package Code Packaging
AL8807BMP-13 MP MSOP-8EP 2500 12mm -13
Marking Information
(1) MSOP-8EP
NEW PRODUCT
(Top View)
8 7 6 5
Logo
Part Number
AL8807B
Y W X E
1 2 3 4
Part Number Package
AL8807BMP-13 MSOP-8EP
Package Outline Dimensions
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.
(1) MSOP-8EP
D
(All dimensions in mm.)
x
y
E
E2
1
e
A1
A
D
8Xb
A3
A2
D1
E3
E1
Gauge Plane
Seating Plane
See Detail C
0.25
4
X
1
0
°
Detail C
c
Packing: 13” Tape and Reel
Quantity Tape Width Part Number Suffix
A~Z : Green
MSOP-8EP
Y : Year : 0~9
W : Week: A~Z : 1~26 week;
a~z : 27~52 week;
z represents 52 and 53 week
MSOP-8EP
Dim Min Max Typ
A - 1.10 -
4
X
1
0
°
a
L
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
AL88070B
Document number: DS36191 Rev. 1 - 2
17 of 18
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March 2014
© Diodes Incorporated
Page 18
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Suggested Pad Layout
Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.
1) MSOP-8EP
X C
NEW PRODUCT
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).
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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.
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
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
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
G
Y2
X1
AL88070B
Document number: DS36191 Rev. 1 - 2
Y
Y1
IMPORTANT NOTICE
LIFE SUPPORT
18 of 18
www.diodes.com
Dimensions
C 0.650
G 0.450
X 0.450
X1 2.000
Y 1.350
Y1 1.700
Y2 5.300
Value
(in mm)
© Diodes Incorporated
L8807B
March 2014
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