AL5801

AL5801
100V, ADJUSTABLE CURRENT SINK LINEAR LED DRIVER
Description
Pin Assignments
The AL5801 combines a 100V N-channel MOSFET with a pre-
(Top View)
biased NPN transistor to make a simple, small footprint LED driver.
The LED current is set by an external resistor connected from REXT
pin (4) to GND pin (6). The internal pre-biased transistor develops
approximately 0.56V across the external resistor.
The AL5801 open-drain output can operate from 1.1V to 100V
enabling it to operate 5V to 100V power supplies without additional
components.
PWM dimming of the LED current can be achieved by driving the
BIAS pin (1) with an external, open-collector NPN transistor or
open-drain N-channel MOSFET.
The AL5801 is available in a SOT26 package and is ideal for driving
LED currents up to 350mA.
SOT26
Features
•
Feedback Pin Reference Voltage VRSET = 0.56V at +25°C
Applications
•
-40°C to +125°C Temperature Range
•
Linear LED Drivers
•
1.1V to 100V Open-Drain Output
•
LED Signs
•
Negative temperature VRSET co-efficient automatically reduces
•
Offline LED Luminaries
the LED current at high temperatures
•
Low thermal impedance SOT26 package with copper lead
frame
•
Lead-Free Finish; RoHS Compliant (Notes 1 & 2)
•
Halogen and Antimony Free. “Green” Device (Note 3)
•
Qualified to AEC-Q101 Standards for High Reliability
Notes:
1. EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant. All applicable RoHS exemptions applied.
2. See http://www.diodes.com 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 Applications Circuit
AL5801
Document number: DS35555 Rev. 3 - 2
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AL5801
Pin Descriptions
Pin
Number
Pin
Name
1
BIAS
Biases the open-Drain output MOSFET
2
3
4
FB
OUT
REXT
5
COMP
Feedback pin
Open-Drain LED driver output
Current sense pin. LED current sensing resistor should be connected from here to GND
Compensation pin. Connect COMP pin to REXT pin and insert a 1nF ceramic capacitor from COMP
pin to FB pin for improved transient stability
6
GND
Function
Ground reference point for setting the LED current
Functional Block Diagram
Figure 1 Block Diagram
Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.)
Symbol
Values
Unit
VOUT
Output voltage relative to GND
Characteristics
100
V
VBIAS
BIAS voltage relative to GND (Note 4)
20
V
FB voltage relative to GND
6
V
VCOMP
COMP voltage relative to GND
6
V
VREXT
REXT voltage relative to GND
6
V
VFB
350
mA
TJ
Operating junction temperature
-40 to +150
°C
TST
Storage temperature
-55 to +150
°C
IOUT
Note:
Output current
4. With pins 5 and 6 connected together.
These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure.
Operation at the absolute maximum rating for extended periods may reduce device reliability.
AL5801
Document number: DS35555 Rev. 3 - 2
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AL5801
Package Thermal Data
Characteristic
Symbol
Value
0.75
Power Dissipation (Note 5) @ TA = +25°C
Power Dissipation (Note 6) @ TA = +25°C
0.70
PD
Power Dissipation (Note 7) @ TA = +25°C
1.05
Thermal Resistance, Junction to Ambient Air (Note 5) @ TA = +25°C
165
Thermal Resistance, Junction to Ambient Air (Note 6) @ TA = +25°C
180
RθJA
Thermal Resistance, Junction to Ambient Air (Note 7) @ TA = +25°C
W
0.85
Power Dissipation (Note 8) @ TA = +25°C
°C/W
145
120
Thermal Resistance, Junction to Ambient Air (Note 8) @ TA = +25°C
Notes:
Unit
5. Device mounted on 15mm x 15mm 2oz copper board.
6. Device mounted on 25mm x 25mm 1oz copper board.
7. Device mounted on 25mm x 25mm 2oz copper board.
8. Device mounted on 50mm x 50mm 2oz copper board.
Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Symbol
Min
Max
VBIAS
Supply voltage range
3.5
20
VOUT
OUT voltage range
1.1
100
ILED
LED pin current (Note 9)
25
350
mA
Operating ambient temperature range
-40
125
°C
TA
Note:
Parameter
Unit
V
9. Subject to ambient temperature, power dissipation and PCB.
NMOSFET Electrical Characteristics: (Q1) (@TA = +25°C, unless otherwise specified.)
Characteristic
OFF CHARACTERISTICS
Symbol
Min
Typ
Max
Unit
Test Condition
Drain-Source Breakdown Voltage
BVDSS
100
⎯
⎯
V
VGS = 0V, ID = 250µA
Zero Gate Voltage Drain Current
IDSS
⎯
⎯
1
µA
VDS = 60V, VGS = 0V
Gate-Source Leakage
IGSS
⎯
⎯
±100
nA
VGS = ±20V, VDS = 0V
VGS(th)
2.0
⎯
4.1
V
VDS = VGS, ID = 250µA
RDS (ON)
⎯
⎯
⎯
0.85
0.99
Ω
VGS = 10V, ID = 1.5A
VGS = 6V, ID = 1A
ON CHARACTERISTICS
Gate Threshold Voltage
Static Drain-Source On-Resistance
Forward Transconductance
gfs
⎯
0.9
⎯
S
VDS = 15V, ID = 1A
Diode Forward Voltage
VSD
⎯
0.89
1.1
V
VGS = 0V, IS = 1.5A
DYNAMIC CHARACTERISTICS
Ciss
⎯
129
⎯
pF
Output Capacitance
Coss
⎯
14
⎯
pF
Reverse Transfer Capacitance
Crss
⎯
8
⎯
pF
Input Capacitance
AL5801
Document number: DS35555 Rev. 3 - 2
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VDS = 50V, VGS = 0V
f = 1.0MHz
July 2012
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AL5801
Pre-Bias Transistor Electrical Characteristics: (Q2) (@TA = +25°C, unless otherwise specified.)
Characteristic (Note 10)
Symbol
Min
Typ
Max
Unit
VI(off)
0.4
-
-
V
Input Voltage
Test Condition
VCC = 5V, IO = 100μA
VI(on)
-
-
1.5
V
VCC = 0.3V, IO = 5mA
Output Voltage
VO(on)
-
0.05
0.3
V
IO/II = 5mA/0.25mA
Output Current
IO(off)
-
-
0.5
μA
VCC = 50V, VI = 0V
DC Current Gain
G1
80
-
-
-
VO = 5V, IO = 10mA
Input Resistance
R1
3.2
4.7
6.2
kΩ
-
Resistance Ratio
R2/R1
8
10
12
-
-
Notes:
10. Short duration pulse test used to minimize self-heating effect.
1.2
1.2
1.0
1.0
MAX POWER DISSIPATION (W)
MAX POWER DISSIPATION (W)
Thermal Characteristics
50mm x 50mm
(2oz. FR4)
0.8
25mm x 25mm
(2oz. FR4)
15mm x 15mm
(2oz. FR4)
0.6
0.4
0.2
0
0
25
50
75
100
TEMPERATURE (°C)
Figure 2 Derating Curve
125
TA = 25°C
2oz. FR4
0.8
0.6
0.4
0.2
0
150
0
500
1,000
1,500
2,000
2
COPPER AREA (mm )
Figure 3 Area vs. Max Power
2,500
180
JUNCTION TO AMBIENT AIR
THERMAL RESISTANCE (°C/W)
160
140
T A = 25°C
25mm x 25mm
1oz. FR4
120
D = 0.5
100
80
D = 0.1
D = 0.2
60
D = 0.05
Single Pulse
40
20
0
0.0001
AL5801
Document number: DS35555 Rev. 3 - 2
0.001
0.01
0.1
1
10
PULSE WIDTH (s)
Figure 4 Transient Thermal Impedance
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100
1,000
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AL5801
Typical Performance Characteristics
0.40
400
Ibias = 0.1mA
0.30
300
0.25
250
0.20
0.15
200
150
REXT = 3.75Ω
0.10
100
0.05
0
Ibias = 0.1mA
350
REXT = 1.6Ω
IOUT (mA)
IOUT (A)
0.35
50
REXT = 11.6Ω
REXT = 22.7Ω
0
1
2
VOUT (V)
Figure 5 Output Current vs. VOUT
0
1
3
0.5
10
REXT (Ω)
Figure 6 Output Current vs. REXT
0.20
TA = -40°C
T A = -40°C
0.4
0.15
T A = 25°C
TA = 25°C
IOUT (A)
0.3
IOUT (A)
100
TA = 85°C
0.2
Ibias = 0.1mA
0.05
REXT = 1.6Ω
0.1
T A = 85°C
0.10
Ibias = 0.1mA
REXT = 3.75Ω
0
0
1
2
VOUT (V)
Figure 7 Output Current vs. VOUT
0
3
0.06
4
6
8
VOUT (V)
Figure 8 Output Current vs. VOUT
10
TA = -40°C
0.030
T A = -40°C
0.05
0.025
IOUT (A)
TA = 25° C
IOUT (A)
2
0.035
0.07
0.04
TA = 85° C
0.03
0.02
TA = 25°C
0.020
T A = 85°C
0.015
0.010
Ibias = 0.1mA
0.01
0
0
0
5
10
VOUT (V)
Figure 9 Output Current vs. VOUT
AL5801
Document number: DS35555 Rev. 3 - 2
Ibias = 0.1mA
0.005
REXT = 11.6Ω
0
15
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REXT = 22.7Ω
0
5
10
15
VOUT (V)
Figure 10 Output Current vs. VOUT
20
July 2012
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AL5801
800
400
700
350
600
300
500
250
IOUT (mA)
VREXT (mV)
Typical Performance Characteristics (cont.)
400
150
200
100
Ibias = 0.1mA
Vbias = 5V
0
-50
Document number: DS35555 Rev. 3 - 2
25mm x 25mm
(2oz. FR4)
15mm x 15mm
(2oz. FR4)
50
0
0
50
100
150
JUNCTION TEMPERATURE (°C)
Figure 11 VREXT vs. Junction Temperature
AL5801
50mm x 50mm
(2oz. FR4)
200
300
100
Ibias = 0.1mA
T A = 85°C
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1
10
VOUT (V)
Figure 12 Output Current vs. VOUT
100
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AL5801
Application Information
Figure 13 Typical Application Circuit for
Linear Mode Current Sink LED Driver
The AL5801 is designed for driving high brightness LEDs with typical LED current up to 350mA. It provides a more cost effective way for driving
low current LEDs when compared against more complex switching regulator solutions. Furthermore, it reduces the PCB board area of the
solution because there is no need for external components like inductors, capacitors and/or switching diodes.
Figure 13 shows a typical application circuit diagram for driving an LED or a string of LEDs. The NPN transistor Q2 measures the LED current by
sensing the voltage across an external resistor REXT. Q2 uses its VBE as reference to set the voltage across REXT and controls the gate voltage of
MOSFET Q1. Q1 operates in linear mode to regulate the LED current. The LED current is:
ILED = VRSET / REXT
where VRSET is the VBE of Q2. VBE is 0.56V typical at a +25°C device temperature. See Figure 11 for the variation of VBE with Q2’s junction
temperature at IBIAS = 0.1mA. VBE has a negative temperature coefficient which reduces the LED current as the device warms up, protecting the
LED(s).
RBIAS should be chosen to drive 0.1mA current into the BIAS pin
RBIAS = ( VCC – 3.75V ) / 0.1mA
From the above equation, for any required LED current the necessary external resistor REXT can be calculated from
REXT = VRSET / ILED
The expected linear mode power dissipation must be factored into the design consideration. The power dissipation across the device can be
calculated by taking the maximum supply voltage less the minimum voltage across the LED string.
VDS(Q1) = VCC(max) – VLED(min) – VRSET
PD = VDS(Q1) * ILED
As the output LED current of AL5801 increases so will its power dissipation. The power dissipation will cause the device temperature to rise
above ambient, TA, by an amount determined by the package thermal resistance, RθJA.
Therefore, the power dissipation supported by the device is dependent upon the PCB board material, the copper area and the ambient
temperature. The maximum dissipation the device can handle is given by:
PD = ( TJ(MAX) - TA ) / RθJA
TJ(MAX) = +150°C is the maximum device junction temperature. Refer to the thermal characteristic graphs in Figure 2 to 4 for selecting the
appropriate PCB copper area. Figure 12 shows the current capabilities of the AL5801 at +25°C with different PCB copper area heat sinks.
AL5801
Document number: DS35555 Rev. 3 - 2
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AL5801
Constant LED Current Temperture Compensation
Variation in the junction temperature of Q2 will cause variations in the value of controlled LED current ILED. The base-emitter VBE voltage of Q2
decreases with increasing temperature at a rate of approximately 2mV/°C. Figure 14 shows a simple temperature compensation network, which
comprises of an NTC thermistor and resistor Rbase, for stabilizing the LED current.
Figure 14 Constant LED Current Temperature Compensation for AL5801
The voltage drop VRSET in the sense resistor REXT should be set to be 40 to 100mV higher than the VBE(Q2) at 25ºC. Figure 11 shows the typical
VBE(Q2) is 0.56V at room temperature with 0.1mA IBIAS, so VRSET is selected to be 0.62V.
With the VRSET chosen, the sense resistor value for 350mA ILED is determined by
REXT = VRSET / ILED = 0.62V / 350mA = 1.77Ω
So a standard resistor value of 1.78Ω with 1% tolerance is used.
The RTH resistance of the NTC thermistor at room temperature is recommended as 10kΩ. The value of base resistor Rbase is set to be 470Ω.
Q2’s base current is obtained as
IB(Q2) = ( VRSET - VBE(Q2) ) / Rbase - VBE(Q2) / RTH = ( 0.62V - 0.56 ) / 470Ω - 0.56V / 10kΩ = 72µA
T
When VBE(Q2) is changed to VBE as the temperature increases to TºC, the thermistor resistance at T°C required to compensate this variation is
given by
T
T
T
RTH = VBE / (( VRSET - VBE ) / Rbase - IB(Q2) )
At -2mV/°C, VBE(Q2) reduces to 0.44V from 0.56V as the temperature increases from +25°C to +85°C. From the above equation, the thermistor’s
resistance at +85°C to keep the same output current is given by
85
RTH = 0.44V / (( 0.62V – 0.44V ) / 470Ω - 72µA ) = 1.4kΩ
The NTC thermistor is chosen for compensation whose resistance is 10kΩ at +25°C and 1.38kΩ at +85°C with a β value of 3530.
Figure 15 shows the ILED variation with temperature with and without temperature compensation.
Figure 15 LED Current Variation with and
without Temperature Compensation
AL5801
Document number: DS35555 Rev. 3 - 2
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AL5801
PWM Dimming
(b)
(a)
Figure 16 Application Circuits for LED Driver with PWM Dimming Functionality (a) MOSFET driving and (b) Transistor driving
PWM dimming can be achieved by driving the BIAS pin (1). An external open-collector NPN transistor or open-drain N-channel MOSFET can be
used to drive the BIAS pin as shown in Figure 16. Dimming is achieved by turning the LEDs ON and OFF for a portion of a single cycle. The
PWM signal can be provided by a micro-controller or by analog circuitry.
Figure 17 shows the LED current against the PWM signal duty ratio when the AL5801 is used to drive three series connected LEDs from a 12V
supply. The PWM dimming frequency is set to 200Hz. The PWM signal is supplied to the open-Drain small signal MOSFET’s gate as shown in
Figure 16a. The BIAS pin signal is an inversion of the PWM drive to the MOSFET’s gate. Therefore, a PWM signal duty cycle of 0% provides the
maximum LED current. Sufficiently large PCB copper area is used for heat sinking of the AL5801 in order to minimize the device self-heating at
+25°C ambient.
Figure 17 LED Current against PWM Dimming Signal Duty Ratio at 200Hz PWM Frequency
AL5801
Document number: DS35555 Rev. 3 - 2
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AL5801
Ordering Information
Green
Green
7” Tape and Reel
Part Number
Qualification
Package
Code
Packaging
(Note 11)
Quantity
Part Number Suffix
AL5801W6-7
AL5801W6Q-7
Commercial
Automotive
W6
W6
SOT26
SOT26
3,000/Tape & Reel
3,000/Tape & Reel
-7
-7
Notes:
11. For packaging details, go to our website at http://www.diodes.com
Marking Information
L100 = Product Type Marking Code
YM = Date Code Marking
Y = Year (ex: Y = 2012)
M = Month (ex: 9 = September)
Date Code Key
Year
Code
Month
Code
Jan
1
2012
Z
2013
A
Feb
2
Mar
3
2014
B
Apr
4
May
5
2015
C
Jun
6
2016
D
Jul
7
Aug
8
2017
E
Sep
9
Oct
O
2018
F
Nov
N
Dec
D
Package Outline Dimensions (All dimensions in mm.)
A
B C
H
K
M
J
L
D
SOT26
Dim Min Max Typ
A
0.35 0.50 0.38
B
1.50 1.70 1.60
C
2.70 3.00 2.80
D
⎯
⎯ 0.95
H
2.90 3.10 3.00
J
0.013 0.10 0.05
K
1.00 1.30 1.10
L
0.35 0.55 0.40
M
0.10 0.20 0.15
0°
8°
α
⎯
All Dimensions in mm
Suggested Pad Layout
C2
Z
C2
Dimensions Value (in mm)
Z
3.20
G
1.60
X
0.55
Y
0.80
C1
G
C1
C2
Y
2.40
0.95
X
AL5801
Document number: DS35555 Rev. 3 - 2
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AL5801
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AL5801
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