AL8861
40V 1.5A BUCK LED DRIVER
Description
The AL8861 is a hysteresis mode DC-DC step-down converter,
designed for driving single or multiple series connected LEDs
efficiently from a voltage source higher than the LED voltage. The
device can operate from an input supply between 4.5V and 40V and
provide an externally adjustable output current up to 1A for TSOT25
package and 1.5A for SOT89-5 and MSOP-8EP packages. Depending
upon supply voltage and external components, this converter can
provide up to 40W of output power.
The AL8861 integrates the power switch and a high-side output
current sensing circuit, which uses an external resistor to set the
nominal average output current.
Dimming can be realized by applying an external control signal to the
V
SET
Pin. The V
SET
Pin will accept either a DC voltage signal or a
PWM signal.
Pin Assignments
(Top View)
L
X
GND
V
SET
TSOT25
(Top View)
V
IN
NEW PRODUCT
I
SENSE
L
X
The soft-start time can be adjusted by an external capacitor from the
V
SET
Pin to Ground. Applying a voltage of 0.2V or lower to the V
SET
Pin can turn off the output and make the device enter into standby
state with low current consumption.
1
5
V
IN
GND
2
3
SOT89-5
Features
Low BOM Counts
Wide Input Voltage Range: 4.5V to 40V
Output Current up to 1.5A
Internal 40V NDMOS Switch
Typical 5% Output Current Accuracy
Single Pin for On/Off and Brightness Control by DC Voltage or
PWM Signal
Recommended Analog Dimming Range: 5% to 100%
Soft-Start
High Efficiency (Up to 97%)
LED Short Protection
Inherent Open-Circuit LED Protection
R
S
Short Protection
Over Temperature Protection (OTP)
Up to 1MHz Switching Frequency
Pb-free TSOT25, SOT89-5 and MSOP-8EP Packages
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
V
SET
4
I
SENSE
I
SENSE
V
IN
L
X
V
SET
L
X
MSOP-8EP
Applications
LED Retrofit for Low Voltage Halogen
Low Voltage Industrial Lighting
LED Backlighting
Illuminated Signs
External Driver with Multiple Channels
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.
AL8861
Document number: DS39435 Rev. 3 - 2
1 of 18
www.diodes.com
October 2017
© Diodes Incorporated
AL8861
Typical Applications Circuit
NEW PRODUCT
V
IN
V
IN
V
SET
I
SENSE
L
X
Pin Descriptions
Pin Number
TSOT25/
SOT89-5
1
2
Pin Name
MSOP-8EP
5, 6
2, 3
L
X
GND
Drain of NDMOS Switch
Ground (0V)
Multi-Function On/Off and Brightness Control Pin:
Leave floating for normal operation
Drive to voltage below 0.2V to turn off output current
Drive with DC voltage (0.3V < V
SET
< 2.5V) to adjust output current from 0 to 100% of
I
OUTNOM
. Linear adjustment range from 5% to 100% of I
OUTNOM
Drive with PWM signal from open-collector or open-drain transistor, to adjust output
current.
Linear adjustment range from 1% to 100% of I
OUTNOM
for f < 500Hz
Connect a capacitor from this pin to Ground to increase soft-start time. (Default soft-start
time = 0.1ms. Additional soft-start time is approximately 1.5ms/1nF)
Connect resistor R
S
from this pin to V
IN
to define nominal average output current.
I
OUTNOM
= 0.1/R
S
Input voltage (4.5V to 40V). Decouple to Ground with 10μF or higher X7R ceramic capacitor
close to device.
No Connection
Function
3
4
V
SET
4
5
—
1
8
7
I
SENSE
V
IN
N/C
AL8861
Document number: DS39435 Rev. 3 - 2
2 of 18
www.diodes.com
October 2017
© Diodes Incorporated
AL8861
Functional Block Diagram
I
SENSE
V
IN
NEW PRODUCT
4.5V
L
X
VDD
Generator
4.5V Drv
Current
Monitor
Current
Limiter
BG &
Reference
Ref
Hysteresis
Control
Comp
PWM
Logic & Driver
V
SET
PWM/DC
Dimming
PWM
OTP
OTP
GND
Absolute Maximum Ratings
(Note 4)
Symbol
V
IN
V
LX
,V
ISENSE
V
VSET
T
J
T
STG
T
LEAD
θ
JA
Input Voltage
L
X
, I
SENSE
Pin Voltage
V
SET
Pin Voltage
Operating Junction Temperature
Storage Temperature Range
Lead Temperature (Soldering, 10sec)
Thermal Resistance (Junction to Ambient)
Parameter
Rating
-0.3 to +42
-0.3 to +42
-0.3 to +6
+150
-65 to +150
+260
TSOT25 (Note 5)
SOT89-5 (Note 6)
MSOP-8EP (Note 7)
TSOT25 (Note 5)
SOT89-5 (Note 6)
MSOP-8EP (Note 7)
147
116
56
27
24
15
Unit
V
V
V
°
C
°
C
°
C
°
C/W
θ
JC
Thermal Resistance (Junction to Case)
°
C/W
Note:
4. Stresses greater than those listed under ―Absolute Maximum Ratings‖ may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under ―Recommended Operating Conditions‖ is not implied.
Exposure to ―Absolute Maximum Ratings‖ for extended periods may affect device reliability.
5. Device mounted on 1"x1" FR-4 MRP substrate PC board, 2oz cooper, with minimum recommended pad layout.
6. Device mounted on 1"*1" FR-4 substrate PC board, 2oz copper, with minimum recommended pad layout.
7. Device mounted on 2"*2" FR-4 substrate PC board, 2oz copper, with minimum recommended pad layout.
AL8861
Document number: DS39435 Rev. 3 - 2
3 of 18
www.diodes.com
October 2017
© Diodes Incorporated
AL8861
Recommended Operating Conditions
Symbol
V
IN
f
SW
I
OUT
T
A
Input Voltage
Switching Frequency
Continuous Output Current
Operating Ambient Temperature
Operating Junction Temperature
Recommended Analog Dimming Range
TSOT25
SOT89-5
MSOP-8EP
Parameter
Min
4.5
—
—
—
—
-40
-40
5
Max
40
1
1
1.5
1.5
+85
+125
100
Unit
V
MHz
A
°
C
°
C
%
NEW PRODUCT
T
J
—
Electrical Characteristics
Symbol
SUPPLY VOLTAGE
V
IN
I
Q
I
SHDN
V
SENSE
V
SENSE_HYS
I
SENSE
V
EN
V
EN(ON)
V
EN(OFF)
R
LX
I
LX(LEAK)
t
SS
f
LX
t
ON_REC
f
LX(MAX)
D
LX(MAX)
D
LX
t
PD
T
OTP
T
OTP_HYS
I
XL(MAX)
Note:
(@V
IN
= 16V, T
A
= +25° unless otherwise specified.)
C,
Conditions
Min
Typ
Max
Unit
Parameter
Input Voltage
Quiescent Current
Shutdown Supply Current
Mean Current Sense Threshold Voltage
Sense Threshold Hysteresis
I
SENSE
Pin Input Current
V
SET
Range on V
SET
Pin
DC Voltage on V
SET
Pin to Enable
DC Voltage on V
SET
Pin to Disable
L
X
Switch On-Resistance
L
X
Switch Leakage Current
Soft-Start Time
Operating Frequency
Recommended Minimum Switch ON
Time
Recommended Maximum Switch
Frequency
Max Duty Circle
Recommended Duty Cycle Range
—
V
SET
Pin Floating, V
IN
= 16V
V
SET
Pin Grounded
Measured on I
SENSE
Pin with
Respect to V
IN
—
V
SENSE
= V
IN
-0.1V
For Analog Dimming
V
EN
Rising
V
EN
Falling
@I
LX
= 100mA
—
V
IN
= 16V, C
EN
= 1nF
V
I
= 16V, V
O
= 9.6V (3 LEDs)
L = 47μF, ΔI = 0.25A (I
LED
= 1A)
For 4% Accuracy
—
—
—
4.5
—
—
96
—
—
0.3
—
—
—
—
—
—
—
—
—
25
—
—
—
2
—
0.55
55
100
±13
8
—
0.25
0.2
0.2
—
1.5
250
500
—
98
—
45
+150
+30
—
40
—
100
104
—
—
2.5
—
—
—
5
—
—
—
1.0
—
75
—
—
—
—
V
mA
µA
mV
%
µA
V
V
V
Ω
μA
ms
kHz
ns
MHz
%
%
ns
°
C
°
C
A
Internal Comparator Propagation Delay
—
(Note 8)
Overtemperature Protection
Temp Protection Hysteresis
Current Limit
—
—
Peak Inductor Current
8. Guaranteed by design.
AL8861
Document number: DS39435 Rev. 3 - 2
4 of 18
www.diodes.com
October 2017
© Diodes Incorporated
AL8861
Typical Performance Characteristics
(@T
A
= +25° V
IN
= 16V, unless otherwise specified.)
C,
Quiescent Current vs. Input Voltage
560
540
520
Quiescent Current vs. Temperature
600
580
560
V
IN
=16V
Quiescent Current (
A)
500
480
460
440
420
400
380
360
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Quiescent Current (
A)
540
520
500
480
460
440
420
400
-50
NEW PRODUCT
Input Voltage (V)
-25
0
25
50
o
75
100
125
Temperature ( C)
Shutdown Current vs. Input Voltage
60
58
56
100
90
80
Shutdown Current vs. Temperature
V
IN
=16V
Shutdown Current (
A)
Shutdown Current (
A)
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
54
52
50
48
46
44
42
40
4
70
60
50
40
30
20
10
0
-50
Input Voltage (V)
-25
0
25
50
o
75
100
125
Temperature ( C)
I
SENSE
Threshold Voltage vs. Input Voltage
120
115
PWM Dimming (V
IN
=16V, 3 LEDs, 47μH, R
S
=0.3Ω)
LED Current vs. Duty Cycle
340
320
300
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
0
I
SENSE
Threshold Voltage (mV)
110
105
100
95
90
85
80
75
70
65
60
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Isen_H
Isen_mean
Isen_L
Output Current (mA)
L=47
H,freq=680kHz
f
PWM
=100Hz
f
PWM
=200Hz
f
PWM
=500Hz
f
PWM
=1kHz
Input Voltage (V)
10
20
30
40
50
60
70
80
90
100
Duty Cycle (%)
5 of 18
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October 2017
© Diodes Incorporated
AL8861
Document number: DS39435 Rev. 3 - 2
