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PDF AL8400 Data sheet ( Hoja de datos )
| Número de pieza | AL8400 | |
| Descripción | LINEAR LED DRIVER-CONTROLLER | |
| Fabricantes | Diodes Incorporated | |
| Logotipo |  |
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Green
AL8400 /AL8400Q
LINEAR LED DRIVER-CONTROLLER with 200mV
CURRENT SENSE VOLTAGE and AUTOMOTIVE GRADE
Description
The AL8400 is a 5-terminal adjustable Linear LED driver-controller
offering excellent temperature stability and output handling capability.
The AL8400 simplifies the design of linear and isolated LED drivers.
With its low 200mV current sense FB pin, it controls the regulation of
LED current with minimal power dissipation when compared to
traditional linear LED drivers. This makes it ideal for medium to high
current LED driving.
Pin Assignments
The AL8400 open-collector output can operate from 0.2V to 18V
enabling it to drive external MOSFET and Bipolar transistors. This
enables the MOSFET and Bipolar selection to be optimized for the
chosen application. It also provides the capability to drive longer LED
chains, by tapping VCC from the chain, where the chain voltage may
exceed 18V.
It is available in the space saving low profile SOT353 package.
The AL8400Q is Automotive Grade and is AEC-Q100 Grade 1
qualified.
Applications
• Isolated Offline LED Lamps
• Linear LED Driver
• LED Signs
• Instrumentation Illumination
Features
• Low Reference Voltage (VFB = 0.2V)
• -40 to +125°C Temperature Range
• 3% Reference Voltage Tolerance at +25°C
• Low Temperature Drift
• 0.2V to 18V Open-Collector Output
• High Power Supply Rejection:
(> 45dB at 300kHz)
• AL8400QSE-7 Automotive Grade qualified to AEC-Q100 Grade 1
• SOT353: Available in “Green” Molding Compound (No Br, Sb)
Lead-Free Finish; RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
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
Vcc
GND
AL8400/ AL8400Q
Document number: DS35115 Rev. 4 - 2
RB
3
Vcc
CD OUT 5
AL8400
GND
2
FB 4
E1
1
CL
Q2
RSET
ILED = VREF/RSET
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August 2012
© Diodes Incorporated
1 page  
AL8400 /AL8400Q
Application Information
Description
The AL8400 Linear LED driver controller uses an external pass element to drive the LEDs and uses its FB pin to sense the LED current through
an external resistor RSET. The pass element is driven by the AL8400’s open collector OUT pin which allows the pass element to be either an
NPN transistor or N-channel MOSFET. An external pull-up resistor, RB, is required to be connected from the OUT pin to VCC. This resistor
supplies the output bias current of the AL8400 together with any current which the pass element requires.
In order to maintain the accuracy of the 200mV reference voltage on the FB pin the value of RB should be set so that the OUT pin sinks 1mA.
Stability
As with all ICs, for best stability a 0.1µF minimum (X7R ceramic) power supply decoupling capacitor, CD, connected between VCC and Ground
(See Figure 2) is recommended. CD should be placed as close to the VCC pin as possible < 5mm.
Figure 2 Application Circuit Using Bipolar Transistor
The AL8400 requires an output capacitor, CL in Figure 2, to be connected from the OUT pin to Ground. This capacitor is required to compensate
the current control loop of the AL8400.
This compensation capacitor must be placed as close to the OUT pin as possible < 5mm. If the PCB traces are too long, there is the possibility of
oscillation at about 5MHz. The capacitors CD and CL must be mounted immediately adjacent to the AL8400, with direct connections to OUT, E1,
GND and VCC. The limit of 5mm provides a good margin for stability.
The value of capacitor CL is determined from the value of the pull-up resistor RB so that:
CL x RB ≥ 2ms
For example if RB = 1kΩ, then CL must be 2µF or greater. The recommended capacitor type is X7R ceramic.
200 225
VOUVTO=UT 0=.06.6VV
150
RB C=O1UTk=Ω2.2uF
CL = 2.2µF
180
100 135
50 90
0 45
Gain
Phas e
-50
1
0
10 100 1k 10k 100k 1M
Frequency (Hz)
Figure 3 Gain and Phase vs. Frequency with RB = 1kΩ and CL = 2.2µF
AL8400/ AL8400Q
Document number: DS35115 Rev. 4 - 2
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August 2012
© Diodes Incorporated
5 Page 
AL8400 /AL8400Q
Application Information (cont.)
High Voltage Operation
The AL8400 also provides the capability to drive longer LED chains as the voltage across the LED chain is determined by the external switch.
The lower supply voltage for the AL8400 can be derived from the supply to the LED chain either by putting a series resistor to the AL8400’s VCC
pin and putting a suitable zener diode from its VCC to GND Figure 10 or by tapping its VCC from the LED chain Figure 11.
Figure 10 High Voltage Operation with Zener Diode from VIN
Equations 1 and 2 (from page 7) now transform into:
LED Circuit Path:
1. VIN = (VLED + VCE + VFB)
Control Drive Circuit Path
2. VCC = (VRB + VBE + VFB)
When the supply voltage for the AL8400 is derived using a zener diode, care has to be taken in dimensioning the resistor R1. The current taken
through R1 from VIN has to be large enough to polarize the zener, bias the AL8400 supply current, AL8400 output current and the pass transistor
across all input voltage variations.
An alternative way of operating the AL8400 from rails greater than 18V is to take its power supply from the LED chain itself.
Figure 11 High Voltage Operation Tapping VCC from the LED String
When the supply voltage for the AL8400 is derived from the LED string, care has to be taken in dimensioning the resistor RB. The current spilled
from the LED chain can reduce the accuracy of the system and brightness matching between the LED.
AL8400/ AL8400Q
Document number: DS35115 Rev. 4 - 2
11 of 13
www.diodes.com
August 2012
© Diodes Incorporated
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet AL8400.PDF ] | |
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