Diodes AL8807Q User Manual

A

Description

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

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

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 AL8807Q is set via an external resistor

connected between the V

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

and SET input pins. Dimming is achieved

IN

Features

AUTOMOTIVE GRADE BUCK LED DRIVER

Pin Assignments

SET

GND

GND

CTRL

Applications

L8807Q

HIGH EFFICIENCY LOW 30V 1.3A

(Top View)

V

IN

N/C

SW

SW

MSOP-8EP

 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 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

 Automotive Interior LED Lamps

 Automotive Exterior LED Lamps

AL8807Q

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Pin Descriptions

Pin Name Pin Number Functions

SET 1 Set Nominal Output Current Pin. Configure the output current of the device.

GND 2, 3 GND Pin

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

VIN

EP EP

Functional Block Diagram

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
 Drive with DC voltage (0.5V < V
 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.

8

Input Supply Pin. Must be locally decoupled to GND with >
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.

= 2.5V giving nominal average output current I

REF

< 2.5V) to adjust output current from 20% to 100% of I

CTRL

2.2µF X7R ceramic capacitor – see applications

OUTnom

= 0.1/RS)

L8807Q

OUTnom

Absolute Maximum Ratings

Symbol Parameter Ratings Unit

ESD HBM Human Body Model ESD Protection 4000 V

ESD MM Machine Model ESD Protection 300 V

ESD CDM Charged Device Model ESD Protection 1000 V

VIN Continuous VIN pin voltage relative to GND

VSW

V

CTRL

I

SW-RMS

I

SW-PK

TJ

T

LEAD

TST

Caution: Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only;

AL8807Q

Document number: DS36904 Rev. 1 - 2

SW voltage relative to GND -0.3 to +40 V

CTRL pin input voltage -0.3 to +6 V

DC or RMS Switch current 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.

(@TA = +25°C, unless otherwise specified.)

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L8807Q

Recommended Operating Conditions (@T

= +25°C, unless otherwise specified.)

A

Symbol Parameter Min Max Unit

VIN

V

CTRLH

V

CTRLDC

V

CTRLL

fSW

ISW

TJ

Operating Input Voltage relative to GND 6.0 30 V

Voltage High for PWM dimming relative to GND 2.6 5.5 V

Voltage range for 20% to 100% DC dimming relative to GND 0.5 2.5 V

Voltage Low for PWM dimming relative to GND 0 0.4 V

Maximum switching frequency — 1 MHz

Continuous switch current — 1.3 A

Junction Temperature Range -40 125 °C

Electrical Characteristics (@ V

= 12V, TA = +25°C, unless otherwise specified.)

IN

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

I

SW_Leakage

JA

JC

Notes: 5. AL8807Q does not have a low power standby mode but current consumption is reduced when output switch is inhibited: V
tested with V

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.

Internal regulator start up threshold

Internal regulator hysteresis threshold

Quiescent current Output not switching (Note 5) — — 350 µA

Input supply Current CTRL pin floating f = 250kHz — 1.8 5 mA

Set current Threshold Voltage — 95 100 105 mV

Set threshold hysteresis — — ±20 — mV

SET pin input current

CTRL pin input resistance Referred to internal reference — 50 — kΩ

Internal Reference Voltage — — 2.5 — V

On Resistance of SW MOSFET

SW rise time

SW fall time — 20 — ns

Switch leakage current

Thermal Resistance Junction-to-

Ambient (Note 6)

Thermal Resistance Junction-to-case

(Note 8)

≤ 2.5V

CTRL

VIN rising

VIN falling

V

= VIN-0.1

SET

ISW = 1A

= 100±20mV, fSW = 250kHz

V

SENSE

V

= 0.1V~12V~0.1V CL = 15pF

SW

VIN =30V

— — 5.9 V

100 — 300 mV

— 16 22 µA

— 0.25 0.4 Ω

— 12 — ns

— — 0.5 μA

(Note 7) — 69 — C/W

(Note 7) — 4.3 — —

= 0V. Parameter is

SENSE

AL8807Q

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F

REQ

UENCY

H

CUR

REN

T

Typical Performance Characteristics (@T

400

350

300

250

200



IN

I (µA)

150

V = 0V

CTRL

V = V

SET IN

°

T = 25C

A

= +25°C, unless otherwise specified.)

A

900

800

L = 33µH

700

z)

600

(k

L = 68µ H

500

400

300

V = 12V

IN

1 LED
R = 150m

SET

T = 25°C

A

L8807Q



100

50

0

0 5 10 15 20 25 30

V (V)

IN

Supp ly Curr ent (not s wit ching) vs . Inpu t Current

100

90

70

(A)

60

40

LED

30

20

0

0.0 0.5 1.0 1.5 2.0 3.0 3.5 4.0 4.5 5.0 5.5

2.5

CTRL PIN VOLTAGE (V)

Figure 3. LED Current vs. V

3

2.5

2

CTRL

200

L = 100µH

100

0

01234

V

CTRL

Figure 2. Switching Frequency vs. V

CTRL

5

80

V = V = 12V

SET IN

60

T = 25°C

A

40

20

CTRL

0

I (µA)

-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 4. I vs. V

CTRL

CTRL CTRL

2.52

V = Open

CTRL

V = V= 12V

SET IN

2.51

1.5

CTRL

V (V)

1

0.5

0

0 5 10 15 20 25 30

V (V)
V vs. In put Voltage

(CTRL pin o pen circui t)

IN

CTRL

V= Open

CTRL

V = V

SET IN

T = 25C

A



2.50

CTRL

V (V)

2.49

2.48

-40 -15 10 35 60 85 110
AMBIENT TEMPERATURE (°C)

Figure 6. V VS. TEMPERATURE

CTRL

AL8807Q

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R

DUT

Y CYC

Typical Performance Characteristics

9

L = 68H, R = 150m

S

T = 25C, V = 12V

AIN

8

CTRL = PWM, f = 500Hz
1 LED

7

6

LED Current
Error

5

4

3

2

LED CURRENT ERROR (%)

1

0

020406080100

Figure 7. I vs. PWM Duty Cycle

400

350

300



(m )

250

DS(ON)

200

150

100

-40 -15 35 60 11010 85

PWM

LED Current

PWM DUTY CYCLE

LED

V = Open

CTRL

V = V= 12V

SET IN

Ambient Temperature ( C)

Figure 9. SW R vs. Temperature

DS(ON)



(cont.) (@TA = +25°C, unless otherwise specified.)

0.8

0.7

200

180

160

0.6

0.5

0.4

0.3
LED CURRENT (A)

0.2

140



120

100

DS(ON)

80

R (m)

60

40

0.1

0

20

0

0 5 10 15

R vs. Input Voltage

DS(ON)

100

90

80

3 LEDS

70

2 LEDS

60

LE (%)

50

40

30

20

10

0

6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 10. Duty Cycle vs. Input Voltage

V (V)

IN

L8807Q

V = Open

CTRL

V = V 12V

SET IN

T = 25C



A

20 25 30

L = 68µH
R = 100m



S

T = 25°C

A

V = Open

CTRL

Figure 11 SW Output Rise Time Figure 12 SW Output Fall Time

AL8807Q

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CUR

RENT ER

ROR

TCHIN

G F

REQ

UEN

C

Y

H

CUR

RENT ERRO

R

TCHING F

REQ

UENC

Y

H

C

U

R

R

N

T

R

ROR

TCH

G

F

REQ

U

C

Y

H

Typical Performance Characteristics 670mA LED Current (cont.) (@T

10

8

6

(%)

4

2

0

-2

-4

-6

LED

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 13. LED Current Deviation vs. Input Voltage

350

300

z)

(k

250

200

150

100

50

SWI

0

6 9 12 15 18 21 24 27 30 33 36

Figure 14. Switching Frequency vs. Input Voltage

L8807Q

= +25°C, unless otherwise specified.)

A

INPUT VOLTAGE (V)

10

8

6

(%)

4

2

0

-2

-4

-6

LED

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 15. LED Current Deviation vs. Input Voltage

10

L = 33µH
R = 150m



S

T = 25°C

A

V = Open

CTRL

1 LED

(%)

8

6

4

2 LEDs

2

E

0

E

LED

3 LEDs

-2

-4

-6

4 LEDs

5 LEDs

6 LEDs

7 LEDs

8 LEDs

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 17. LED Current Deviation vs. Input Voltage

500

450

z)

400

(k

350

300

250

200

150

100

SWI

50

0

6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 16. Switching Frequency vs. Input Voltage

800

L = 33µH
R = 150m



S

700

T = 25°C

600

500

A

V = Open

CTRL

z)

(k

EN

400

300

1 LED

IN

200

4 LEDs

5 LEDs

6 LEDs

SWI

100

3 LEDs

2 LEDs

0

6 9 12 15 18 21 24 27 30 33 36

7 LEDs

8 LEDs

INPUT VOLTAGE (V)

Figure 18. Switching Frequency vs. Input Voltage

AL8807Q

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CUR

RENT ER

ROR

TCHIN

G FREQ

UENCY

H

CUR

RENT ERRO

R

TCHIN

G FREQ

UENCY

H

CUR

R

T ER

ROR

TCH

N

G F

R

Q

UEN

C

Y

H

Typical Performance Characteristics 1A LED Current (cont.) (@T

10

8

6

(%)

4

2

0

-2

-4

-6

LED

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 19. LED Current Deviation vs. Input Voltage

10

8

6

(%)

4

2

0

-2

-4

-6

LED

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 21. LED Current Deviation vs. Input Voltage

350

300

z)

(k

250

200

150

100

50

SWI

2 LEDs

0

6 9 12 15 18 21 24 27 30 33 36

Figure 20. Switching Frequency vs. Input Voltage

350

300

z)

(k

250

200

150

100

50

SWI

0

6 9 12 15 18 21 24 27 30 33 36

Figure 22. Switching Frequency vs. Input Voltage

= +25°C, unless otherwise specified.)

A

L = 100µH
R = 100m



S

T = 25°C

A

V = Open

CTRL

1 LED

7 LEDs

3 LEDs

4 LEDs

5 LEDs

6 LEDs

8 LEDs

INPUT VOLTAGE (V)

INPUT VOLTAGE (V)

L8807Q

10

600

8

z)

6

(%)

4

500

(k

400

2

E

0

EN

-2

-4

-6

LED

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 23. LED Current Deviation vs. Input Voltage

300

I

200

100

SWI

0

6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 24. Switching Frequency vs. Input Voltage

AL8807Q

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CUR

RENT ER

ROR

TCH

G

F

REQ

UENC

Y

H

CUR

RENT ERRO

R

TCHING F

REQ

UENC

Y

H

CUR

R

T ER

ROR

TCHIN

G F

R

Q

U

N

C

Y

H

Typical Performance Characteristics 1.3A LED Current (cont.) (@T

10

8

6

(%)

4

2

0

-2

-4

-6

LED

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 25. LED Current Deviation vs. Input Voltage

10

8

6

(%)

4

2

250

L = 100µH
R = 77m

200

S

T = 25°C

A

V = Open

CTRL

z)

(k

150

100

IN

1 LED

50

SWI

2 LEDs

0

6 9 12 15 18 21 24 27 30 33 36

Figure 26. Switching Frequency vs. Input Voltage

300

L = 68µH
R = 77m

S

T = 25°C

z)

250

A

V = Open

(k

CTRL

200

= +25°C, unless otherwise specified.)

A



3 LEDs

4 LEDs

5 LEDs

6 LEDs

7 LEDs

8 LEDs

INPUT VOLTAGE (V)



L8807Q

0

150

-2

100

-4

-6

LED

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 27. LED Current Deviation vs. Input Voltage

10

8

6

(%)

4

2

0

EN

-2

-4

-6

LED

-8

-10
6 9 12 15 18 21 24 27 30 33 36

INPUT VOLTAGE (V)

Figure 29. LED Current Deviation vs. Input Voltage

1 LED

50

SWI

3 LEDs

4 LEDs

5 LEDs

2 LEDs

0

6 9 12 15 18 21 24 27 30 33 36

6 LEDs

7 LEDs

8 LEDs

INPUT VOLTAGE (V)

Figure 28. Switching Frequency vs. Input Voltage

600

L = 33µH



R = 77m

500

S

T = 25°C

A

V = Open

CTRL

z)

(k

400

E

300

E

200

1 LED

100

SWI

2 LEDs3 LEDs

0

6 9 12 15 18 21 24 27 30 33 36

4 LEDs

5 LEDs

6 LEDs

7 LEDs

8 LEDs

INPUT VOLTAGE (V)

Figure 30. Switching Frequency vs. Input Voltage

AL8807Q

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L8807Q

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 R

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

LED Current Control

The LED current is controlled by the resistor R1 in Figure 30.

. The internal circuit of the AL8807Q senses the voltage across R1 and applies a proportional

1

, L1,

1

, which is sensed by the AL8807Q. A voltage proportional to the sense voltage across R1 is

1

.

1

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



V

I

LED

THD

1R

1.0

66.0

 m150

Figure 30 Typical Application Circuit

=2.5V the resulting resistor is:

CTRL

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:

V

V

CTRL

THD

I 

LED

V

With 0.5V ≤ V

be clamped to approximately 100% and follows

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

REF

≤ 2.5V the LED current varies linearly with V

CTRL

R

SET

, as in figure 2. If the CTRL pin is brought higher than 2.5V, the LED current will

CTRL

V

I 

LED

THD

.

R

SET

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]

L8807Q

Application Information

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

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

600

500

400

300

200

LED current [mA

100

(cont.)

. To

SET

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

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L8807Q

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 (V

= 30V, I

IN

= 667mA, 1 LED)

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

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L8807Q

Application Information

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).

(cont.)

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:

Part No.

MSS1038-333 33 0.093 2.3
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.

AL8807Q

Document number: DS36904 Rev. 1 - 2

L

(µH)

DCR

(V)

I

SAT

(A)

Manufacturer

CoilCraft www.coilcraft.com

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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 Switch ‘Off’ time

IL

IL



t

ON

Where:

L is the coil inductance (H)

is the coil resistance (Ω)RS is the current sense resistance (Ω)

r

L

is the required LED current (A)

I

avg

∆I is the coil peak-peak ripple current (A) {Internally set to 0.3 x Iavg}

V

is the supply voltage (V)

IN

is the total LED forward voltage (V)

V

LED

is the switch resistance (Ω) {=0.5Ω nominal}

R

SW

is the diode forward voltage at the required load current (V)

V

D





x

IVV



RrR

SWLSAVGLEDIN

t

OFF









x

IVV

rR

LSAVGDLED

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 

and ambient temperature.

The maximum power dissipation can be calculated using the following formula:

= (T

P

D(MAX)

The recommended maximum operating junction temperature, T

junction to ambient thermal resistance, 

has been packaged in thermally enhanced MSOP-8EP package.

J(MAX)

− TA) / 

JA

and device power dissipation. To support high LED drive at higher ambient temperatures the AL8807Q

JA

, is 125°C and so maximum ambient temperature is determined by the AL8807Q’s

J

, PCB layout, airflow surrounding the IC, and difference between junction

JA

T

is the maximum operating junction temperature,

J(MAX)

is the ambient temperature, and

T

A

is the junction to ambient thermal resistance.



JA

JA, is layout dependent and the AL8806Q’s JA in MSOP-8EP on a

51 x 51mm double layer PCB with 2oz copper standing in still air is

approximately 69°C/W.

C25C125



= 25°C is:

A



W45.1

www.diodes.com

Therefore the maximum power dissipation at T

P

Figure 35, shows the power derating of the AL8807QMP on an FR4

51x51mm PCB with 2oz copper standing in still air.

As the ambient temperature increases and/or the PCB area reduces

the maximum allowable power dissipated by the AL8807Q will

decrease.





)MAX(D

W/C69



AL8807Q

Document number: DS36904 Rev. 1 - 2

13 of 16

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 35 Derating Curve for Different PCB

MSOP-8EP

Ambient temperature (°C)

L8807Q

March 2014

© Diodes Incorporated

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L8807Q

Application Information

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, L

(cont.)

, See figure 36.

TRACK

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 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 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

AL8807Q

Document number: DS36904 Rev. 1 - 2

the wires are joined to the PCB.

Figure 36 PCB Loop Resonance

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pin and D1 Cathode

IN

and SET pins.

IN

March 2014

© Diodes Incorporated

A

Ordering Information

L8807Q

(Note 10)

Part Number Package Code

Packaging

(Note 9)

Packing: 13” Tape and Reel Qualification Grade

Quantity Tape Width Part Number Suffix

AL8807QMP-13 MP MSOP-8EP 2500 12mm -13 Automotive Grade

Note: 9. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at

10. AL8807Q has been qualified to AEC-Q100 grade 1 and is classified as “Automotive Grade” which supports PPAP documentation.

http://www.diodes.com/datasheets/ap02001.pdf

See AL8807 datasheet for commercial qualified versions.

Marking Information

(1) MSOP-8EP

Part Number Package

AL8807QMP-13 MSOP-8EP

Package Outline Dimensions

(All dimensions in mm.)

Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.

D

x

E

E

2

y

D

1

5
2

.

0

Gauge Plane

Seating Plane

1

e

A

1

A

8Xb

E

3

A

3

A

2

4

X

1

0

°

Detail

c

D

E

1

See Detail

C

Dim Min Max Typ

4

X

1

0

°

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

a

L

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

C

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

MSOP-8EP

All Dimensions in mm

AL8807Q

Document number: DS36904 Rev. 1 - 2

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L8807Q

Suggested Pad Layout

Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.

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.

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

Y2

G

X C

X1

Y

Y1

IMPORTANT NOTICE

LIFE SUPPORT

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)

AL8807Q

Document number: DS36904 Rev. 1 - 2

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