AS1116-BSST(2009) 데이터 시트보기 (PDF) - austriamicrosystems AG
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AS1116-BSST Datasheet PDF : 20 Pages
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AS1116
Datasheet - Typical Application
9 Typical Application
Selecting RSET Resistor Value and Using External Drivers
Brightness of the display segments is controlled via RSET. The current that flows between VDD and ISET defines the
current that flows through the LEDs.
Segment current is about 200 times the current in ISET. Typical values for RSET for different segment currents, operat-
ing voltages, and LED voltage drop (VLED) are given in Table 21 & Table 22. 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 (see Intensity Control Register (0x0A) on page 12).
Table 21. RSET vs. Segment Current and LED Forward Voltage, VDD = 2.7V & 3.3V & 3.6V
ISEG (mA)
40
30
20
10
VLED
1.5V
2.0V
5kΩ 4.4kΩ
6.9kΩ 5.9kΩ
10.7kΩ 9.6kΩ
22.2kΩ 20.7kΩ
1.5V
6.7kΩ
9.1kΩ
13.9kΩ
28.8kΩ
VLED
2.0V
6.4kΩ
8.8kΩ
13.3kΩ
27.7kΩ
2.5V
5.7kΩ
8.1kΩ
12.6kΩ
26kΩ
1.5V
7.5kΩ
10.18kΩ
15.6kΩ
31.9kΩ
VLED
2.0V
2.5V
7.2kΩ 6.6kΩ
9.8kΩ 9.2kΩ
15kΩ 14.3kΩ
31kΩ 29.5kΩ
3.0V
5.5kΩ
7.5kΩ
13kΩ
27.3kΩ
Table 22. RSET vs. Segment Current and LED Forward Voltage, VDD = 4.0V & 5.0V
ISEG
(mA)
40
30
20
10
1.5V
8.6kΩ
11.6kΩ
17.7kΩ
36.89kΩ
2.0V
8.3kΩ
11.2kΩ
17.3kΩ
35.7kΩ
VLED
2.5V
7.9kΩ
10.8kΩ
16.6kΩ
34.5kΩ
3.0V
7.6kΩ
9.9kΩ
15.6kΩ
32.5kΩ
3.5V
5.2kΩ
7.8kΩ
13.6kΩ
29.1kΩ
VLED
1.5V
2.0V
2.5V
3.0V 3.5V 4.0V
11.35kΩ 11.12kΩ 10.84kΩ 10.49kΩ 10.2kΩ 9.9kΩ
15.4kΩ 15.1kΩ 14.7kΩ 14.4kΩ 13.6kΩ 13.1kΩ
23.6kΩ 23.1kΩ 22.6kΩ 22kΩ 21.1kΩ 20.2kΩ
48.9kΩ 47.8kΩ 46.9kΩ 45.4kΩ 43.8kΩ 42kΩ
Calculating Power Dissipation
The upper limit for power dissipation (PD) for the AS1116 is determined from the following equation:
PD = (VDD x 5mA) + (VDD - VLED)(DUTY x ISEG x N)
Where:
VDD is the supply voltage.
DUTY is the duty cycle set by intensity register (page 13).
N is the number of segments driven (worst case is 8)
VLED is the LED forward voltage
ISEG = segment current set by RSET
Dissipation Example:
ISEG = 40mA, N = 8, DUTY = 15/16, VLED = 2.2V at 40mA, VDD = 5V
PD = 5V(5mA) + (5V - 2.2V)(15/16 x 40mA x 8) = 0.865W
Thus, for a QSOP-24 package ΘJA = +88°C/W, the maximum allowed TAMB is given by:
TJ,MAX = TAMB + PD x ΘJA = 150°C = TAMB + 0.865W x 88°C/W
In this example the maximum ambient temperature must stay below 73.88°C.
(EQ 1)
(EQ 2)
(EQ 3)
(EQ 4)
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