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PDF AL8860 Data sheet ( Hoja de datos )
| Número de pieza | AL8860 | |
| Descripción | 40V 1.5A BUCK LED DRIVER | |
| Fabricantes | Diodes | |
| Logotipo |  |
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AL8860
40V 1.5A BUCK LED DRIVER
Description
The AL8860 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 MSOP-8EP package. Depending upon supply
voltage and external components, this converter can provide up to 40
watts output power.
The AL8860 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
CTRL pin. The CTRL pin will accept either a DC voltage signal or a
PWM signal.
The soft-start time can be adjusted by an external capacitor from the
CTRL pin to ground. Applying a voltage of 0.2V or lower to the CTRL
pin can turn off the output and make the device enter into standby
state with low current consumption.
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% ~100%
Soft-Start
High Efficiency (Up to 97%)
LED Short Protection
Inherent Open-Circuit LED Protection
Over Temperature Protection (OTP)
Up to 1MHz Switching Frequency
Pb-Free TSOT25 and MSOP-8EP Packages
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Pin Assignments
(Top View)
TSOT25
(Top View)
MSOP-8EP
Applications
LED Retrofit for Low Voltage Halogen
Low Voltage Industrial Lighting
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.
AL8860
Document number: DS39014 Rev. 1 - 2
1 of 17
www.diodes.com
September 2016
© Diodes Incorporated
1 page  
AL8860
Typical Performance Characteristics (@TA = +25°C, VIN = 16V, unless otherwise specified.)
Quiescent Current vs. Input Voltage
Quiescent Current vs. Temperature
560
540
520
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
Input Voltage(V)
Shutdown Current vs. Input voltage
600
580
560
540
520
500
480
460
440
420
400
-50
-25
V =16V
IN
0 25 50 75
Temperature('C)
100
Shutdown Current vs. Temperature
125
60
58
56
54
52
50
48
46
44
42
40
4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Input Voltage(V)
SET Threshold Voltage vs. Input voltage
120
115
110
105
100
95
90
85
80 VTH_H
75 VTH_mean
70 VTH_L
65
60
4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Input Voltage(V)
100
90
80
70
60
50
40
30
20
10
0
-50
-25
V =16V
IN
0 25 50 75
Temperature('C)
100 125
PWM Dimming (VIN=16V, 3LEDs, 47μH, Rs=0.3Ω)
Output Current vs. Duty Cycle
340
320
300
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
0
L=47H,freq=680kHz
fPWM=100Hz
fPWM=200Hz
fPWM=500Hz
fPWM=1kHz
10 20 30 40 50 60 70 80 90 100
Duty Cycle(%)
AL8860
Document number: DS39014 Rev. 1 - 2
5 of 17
www.diodes.com
September 2016
© Diodes Incorporated
5 Page 
AL8860
Application Information
The AL8860 is a hysteretic mode LED driver with integrated power switch. It is available for two packages that provide a tradeoff between PCB area
and power dissipation capability. It is recommended that for higher LED currents/smaller PCBs that the MSOP-8EP version should be used to
maximize the allowable LED current over a wider ambient temperature range.
AL8860 Operation
In normal operation, when normal input voltage is applied at VIN, the AL8860 internal switch will turn on. Current starts to flow through sense
resistor RS, 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 RS. The internal circuit of the AL8860 senses the voltage across RS 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 RS, L1, LEDs and diode D1, and back to the supply rail, but it decays, with the rate determined by the
forward voltage drop of LEDs and the diode D1.
This decaying current produces a falling voltage on RS, which is sensed by the AL8860. A voltage proportional to the sense voltage across RS will
be applied at the input of 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 RS.
LED Current Configuration
The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS) connected between VIN
and SET and is given by:
The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the typical application
circuit shown on page 1.
RS (Ω)
0.066
0.1
0.13
0.15
0.3
Nominal Average Output Current (mA)
1500
1000
760
667
333
The above values assume that the CTRL pin is floating and at a nominal reference voltage for internal comparator. It is possible to use different
values of RS if the CTRL pin is driven by an external dimming signal.
Analog Dimming
Apply a DC voltage from 0.3V to 2.5V on CTRL pin can adjust output current from 0 to 100% of IOUT_NOM linearly, as shown in Figure 1. If the CTRL
pin is brought higher than 2.5V, the LED current will be clamped to 100% of IOUT_NOM while if the CTRL voltage falls below the threshold of 0.3V,
the output switch will turn off.
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. To achieve a high resolution the PWM
frequency is recommended 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%.
The accuracy of the low duty cycle dimming is affected by both the PWM frequency and also the switching frequency of the AL8860. 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.
AL8860
Document number: DS39014 Rev. 1 - 2
11 of 17
www.diodes.com
September 2016
© Diodes Incorporated
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet AL8860.PDF ] | |
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