FAN5622 Datasheet, PDF (8/13 Pages) Fairchild Semiconductor – Linear LED Drivers with Single-Wire Digital Interface

Circuit Description
The FAN5622, FAN5624, and FAN5626 are a family of
current-sink linear LED driver ICs able to drive two, four, and
six LEDs respectively. These three devices are powered
directly from 2.7V to 5.5V supply and all the channels are
controlled via the integrated current sinks from the external
power source. Designed with a very low drop-out voltage, the
FAN562x products can operate close to the input supply
voltage without the need for additional inductive boost or
capacitive switching circuitry.
All three devices require only two additional discrete passive
components: a single 1µF input ceramic capacitor and a
resistor (R_SET) to set the maximum current for the LEDs. Each
current-sink output provides constant current and can drive
the LEDs up to 30mA. Fairchild Semiconductor’s TinyWire™
single-wire digital interface enables these LED drivers to
program the brightness level of the LEDs in 32 linear steps.
Setting Maximum Current
The maximum LED current of the FAN5622, FAN5624, and
FAN5626 is programmed by an external resistor called RSET.
The maximum full-scale LED current for all three LED drivers
is 30mA and it can go as low as 5mA. The FAN562x products
also operate below 5mA full-scale LED current by using a
larger R_SET value. However, the LED channel accuracy and
matching specifications are guaranteed. Table 1 shows the
RSET resistor values for several full-scale current levels.
Table 1. Maximum LED Current Settings by Resistor
I_LED (mA)
5
10
15
20
25
30
R_SET (kΩ)
56.20
28.70
19.10
14.30
11.50
9.53
Digital Interface & Dimming Control
The FAN5622, FAN5624, and FAN5626 implement a simple
single-wire digital interface to program the LED brightness to
one of thirty two (32) levels spaced in linear steps. To maintain
the brightness of the LEDs at a specific dimming level, the
digital pulse signal to the CTRL pin should be held HIGH for
that last pulse. It is held HIGH for as long as desired to keep
the LEDs illuminated at that specific brightness level.
Table 2 outlines the dimming levels while Figure 17 shows
how to change the dimming levels.
Table 2. Brightness Control Levels (R_SET = 19.10kΩ)
Dimming Level
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Current Level
1.67%
3.33%
5.00%
6.67%
10.00%
13.33%
16.67%
20.00%
23.33%
26.67%
30.00%
33.33%
36.67%
40.00%
43.33%
46.67%
50.00%
53.33%
56.67%
60.00%
63.33%
66.67%
70.00%
73.33%
76.67%
80.00%
83.33%
86.67%
90.00%
93.33%
96.67%
100.00%
I_LED (mA)
0.25
0.50
0.75
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
7.50
8.00
8.50
9.00
9.50
10.00
10.50
11.00
11.50
12.00
12.50
13.00
13.50
14.00
14.50
15.00
© 2010 Fairchild Semiconductor Corporation
FAN5622 / FAN5624 / FAN5626 • Rev. 1.0.2
8
www.fairchildsemi.com