AL8400EV1 User Guide Issue 1

AL8400EV1 EVALUATION BOARD USER GUIDE
DESCRIPTION
The AL8400EV1, Figure 1, is a double sided evaluation board for the AL8400 linear LED driver. The
evaluation board is preset to drive 150mA through the LED string, the maximum number of which
depends on their total forward voltage drop.
The operating voltage is between 4 and 18 volts, depending on the LED string to be driven. Higher
voltages for longer LED strings can be used by tapping off the board Vin from an intermediate point in
the LED string.
Note: The evaluation board does not have reverse supply protection.
The sense resistor R2 of 300mΩ sets the LEDs nominal current at 150mA.
V
LEDs
4-18VDC
Figure 1: AL8400EV1 evaluation board and connection diagram
AL8400EV1 Connection Point Definition
Name
Description
Vin
Positive supply voltage. 4 to 18V
GND
Supply Ground (0V)
LED A
LED K
LED A
LED K
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connects to the external LED string anode
connects to the external LED string cathode
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AL8400EV1
AL8400 DEVICE 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 0.2V 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.
AL8400 DEVICE FEATURES
•
Low reference voltage (VFB = 0.2V)
•
-40 to 125ºC 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)
DEVICE APPLICATIONS
•
Isolated offline LED converters
•
Linear LED driver
•
LED signs
•
Instrumentation illumination
AL8400 Device Packages, Pin and Definitions
SOT353 pack
AL8805 Device Pin Definition
Name
Pin No
Description
E1
1
Emitter connection. Connect to GND.
GND
2
Analog Ground: Ground return for reference and amplifier. Connect
to E1.
VCC
3
Supply Input. Connect a 0.47µF ceramic capacitor close to the device
from VCC to GND.
FB
4
Feedback Input. Regulates to 200mV nominal.
OUT
5
Output. Connect a capacitor close to device between OUT and GND.
ORDERING INFORMATION
EVALBOARD ORDER
NUMBER
AL8400EV1
DEVICE ORDER NUMBER
AL8400SE-7
Please note: Evaluation boards are subject to
availability and qualified sales leads.
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AL8400EV1
AL8400EV1 EVALUATION BOARD REFERENCE DESIGN
TP1
TP4
VIN
LED A
R1
10k
TP5
C
3
C1
470nF
Q1
FZT690B
B
4
C2
470nF
LED K
E
VCC
FB
5
E1
2
1
OUT
GND
U1
GND
IC - AL8400
GND
R2
1R3
TP2
GND
GND
Figure 2: AL8400EV1 Schematic
The AL8400 provides a simple linear LED driver in the form of a constant current circuit. The
device will drive the base of the external transistor, Q1, appropriately to maintain a voltage of 0.2V at
the FB pin. Choosing the value of R2 allows the current in the LED string (and through Q1 and R2) to
be selected.
The board comes preset to 150mA LED current with R2 at 1.3ohms:
ILED = 0.2 ÷ 1.3 = 0.154A
The AL8400 will tolerate a maximum voltage of 18V at its VCC input, but it can be used over
an extended voltage range by taking Vin from an intermediate point in the LED String:
+ve DC input
Vin
AL8400EV1
Board
0V input
GND
LED K
Figure 3: Extended Voltage Range connection diagram
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AL8400EV1
Bill of Materials
QUANTITY
1
1
1
2
1
1
PCB IDENT
N/A
U1
Q1
C1,C2
R1
R2
VALUE
DDB041R1
AL8400
FZT690B
470nF
10k
1R3
DESCRIPTION
PCB
0603 Ceramic Capacitor
0603 Resistor
1206 Resistor
SUGGESTED SOURCE
Diodes Zetex
Diodes Zetex
Diodes Zetex
Generic
Generic
Generic
Circuit Accuracy.
The accuracy of the circuit is determined by the accuracy of the device (+/- 5% over temp)
and the accuracy of the current sensing resistor (Typ +/- 1%).
For the circuit as set the nominal current is 154mA (0.2/1.3 = 0.15384…). The worst cases
are 163mA (0.210/1.287 = 0.16317…) and 144mA (0.19/1.313 = 0.14470…). This gives approx 10mA
possible variation over the nominal 154mA, about 6.5%.
For Further information please contact your Diodes Inc representative.
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AL8400EV1
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