AS1116
Datasheet - Ty p i c a l A p p l i c a t i o n
9 Typical Application
Selecting R
SET
Resistor Value and Using External Drivers
Brightness of the display segments is controlled via R
SET
. The current that flows between V
DD
and I
SET
defines the
current that flows through the LEDs.
Segment current is about 200 times the current in I
SET
. Typical values for R
SET
for different segment currents, operat-
ing voltages, and LED voltage drop (V
LED
) are given in
&
The maximum current the AS1116 can
drive is 47mA. If higher currents are needed, external drivers must be used, in which case it is no longer necessary
that the devices drive high currents.
Note:
The display brightness can also be logically controlled
Table 21. R
SET
vs. Segment Current and LED Forward Voltage, V
DD
= 2.7V & 3.3V & 3.6V
I
SEG
(mA)
V
LED
1.5V
2.0V
1.5V
V
LED
2.0V
2.5V
1.5V
V
LED
2.0V
2.5V
3.0V
40
30
20
10
5k
Ω
6.9k
Ω
10.7k
Ω
22.2k
Ω
4.4k
Ω
5.9k
Ω
9.6k
Ω
20.7k
Ω
6.7k
Ω
9.1k
Ω
13.9k
Ω
28.8k
Ω
6.4k
Ω
8.8k
Ω
13.3k
Ω
27.7k
Ω
5.7k
Ω
8.1k
Ω
12.6k
Ω
26k
Ω
7.5k
Ω
10.18k
Ω
15.6k
Ω
31.9k
Ω
7.2k
Ω
9.8k
Ω
15k
Ω
31k
Ω
6.6k
Ω
9.2k
Ω
14.3k
Ω
29.5k
Ω
5.5k
Ω
7.5k
Ω
13k
Ω
27.3k
Ω
V
DD
= 2.7V
V
DD
= 3.3V
Table 22. R
SET
vs. Segment Current and LED Forward Voltage, V
DD
= 4.0V & 5.0V
I
SEG
(mA)
V
LED
1.5V
2.0V
2.5V
3.0V
3.5V
1.5V
2.0V
V
DD
= 3.6V
V
LED
2.5V
3.0V
3.5V
4.0V
40
30
20
10
8.6k
Ω
8.3k
Ω
11.6k
Ω
11.2k
Ω
17.7k
Ω
17.3k
Ω
36.89k
Ω
35.7k
Ω
7.9k
Ω
7.6k
Ω
5.2k
Ω
10.8k
Ω
9.9k
Ω
7.8k
Ω
16.6k
Ω
15.6k
Ω
13.6k
Ω
34.5k
Ω
32.5k
Ω
29.1k
Ω
11.35k
Ω
15.4k
Ω
23.6k
Ω
48.9k
Ω
11.12k
Ω
15.1k
Ω
23.1k
Ω
47.8k
Ω
10.84k
Ω
10.49k
Ω
14.7k
Ω
14.4k
Ω
22.6k
Ω
22k
Ω
46.9k
Ω
45.4k
Ω
10.2k
Ω
13.6k
Ω
21.1k
Ω
43.8k
Ω
9.9k
Ω
13.1k
Ω
20.2k
Ω
42k
Ω
V
DD
= 4.0V
Calculating Power Dissipation
The upper limit for power dissipation (PD) for the AS1116 is determined from the following equation:
PD = (V
DD
x 5mA) + (V
DD
- V
LED
)(DUTY x I
SEG
x N)
Where:
V
DD
is the supply voltage.
DUTY
is the duty cycle set by intensity register
N
is the number of segments driven (worst case is 8)
V
LED
is the LED forward voltage
I
SEG
= segment current set by RSET
Dissipation Example:
I
SEG
= 40mA, N = 8, DUTY = 15/16, V
LED
= 2.2V at 40mA, V
DD
= 5V
PD = 5V(5mA) + (5V - 2.2V)(15/16 x 40mA x 8) = 0.865W
(EQ 2)
(EQ 3)
(EQ 1)
Thus, for a QSOP-24 package
Θ
JA
= +88°C/W, the maximum allowed T
AMB
is given by:
T
J,MAX
= T
AMB
+ PD x
Θ
JA
= 150°C = T
AMB
+ 0.865W x 88°C/W
(EQ 4)
In this example the maximum ambient temperature must stay below 73.88°C.
www.austriamicrosystems.com
Revision 1.04
V
DD
= 5.0V
15 - 20
AMSCO [ AUSTRIAMICROSYSTEMS AG ]
