A6278 Datasheet, PDF (8/18 Pages) Allegro MicroSystems – Serial-Input Constant-Current Latched LED Drivers with Open LED Detection

A6278 and
A6279
Serial-Input, Constant-Current Latched
LED Drivers with Open LED Detection
Constant Current (R_EXT)
The A6278 and A6279 allow the user to set the magnitude of
the constant current to the LEDs. Once set, the current remains
constant regardless of the LED voltage variation, the supply
voltage variation, or other circuit parameters that could otherwise
affect LED current. The output current is determined by the value
of an external current-control resistor (R_EXT). The relationship of
these parameters is shown in figure 1. Typical characteristics for
output current and V_CE are shown in figure 2 for common values
of R_EXT.
Figure 1. Output Current versus Current Control Resistance
T_A= 25°C, V_CE = 0.7 V
90
80
70
60
50
40
30
20
10
0
101000
200 330000
550000 700 1k1K
R_EXT (Ω)
2k2K
33kK
55kK
90
80
70
60
50
40
30
20
10
0
0
Figure 2. Output Current versus Device Voltage Drop
T_A= 25°C
R_EXT = 225 Ω
R_EXT = 470 Ω
R_EXT = 3900 Ω
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
V_CE (V)
Allegro MicroSystems, Inc.
8
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com