AS1108 查看數據表（PDF） - austriamicrosystems AG
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AS1108 Datasheet PDF : 19 Pages
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AS1108
Data Sheet
austriamicrosystems
Supply Bypassing and Wiring
8 Typical Application
Supply Bypassing and Wiring
In order to achieve optimal performance the AS1108 should be placed very close to the LED display to minimize
effects of electromagnetic interference and wiring inductance.
Furthermore, a 10µF electrolytic and a 0.1µF ceramic capacitor should be connected between pins VDD and GND to
avoid power supply ripple (see Figure 11 on page 14).
Note: Both GND pins must be connected to ground.
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 Tables 18 - 22. The maximum current the AS1108 can drive is
40mA. If higher currents are needed, external drivers must be used, in which case it is no longer necessary that the
device drive high currents.
In cases where the device drives only a few digits, Table 15 specifies the maximum currents, and RSET must be set
accordingly.
Note: The display brightness can also be logically controlled (see Selecting RSET Resistor Value and Using External
Drivers on page 12).
Table 18. RSET vs. Segment Current and LED Forward Voltage, VDD = 2.7V
ISEG (mA)
40
30
20
10
1.5
5kΩ
6.9kΩ
10.7kΩ
22.2kΩ
VLED(V)
2.0
4.4kΩ
5.9kΩ
9.6kΩ
20.7kΩ
Table 19. RSET vs. Segment Current and LED Forward Voltage, VDD = 3.3V
ISEG (mA)
1.5
VLED(V)
2.0
2.5
40
6.7kΩ
6.4kΩ
5.7kΩ
30
9.1kΩ
8.8kΩ
8.1kΩ
20
13.9kΩ
13.3kΩ
12.6kΩ
10
28.8kΩ
27.7kΩ
26kΩ
Table 20. RSET vs. Segment Current and LED Forward Voltage, VDD = 3.6V
ISEG (mA)
40
30
20
10
1.5
7.5kΩ
10.18kΩ
15.6kΩ
31.9kΩ
2.0
7.2kΩ
9.8kΩ
15kΩ
31kΩ
VLED(V)
2.5
6.6kΩ
9.2kΩ
14.3kΩ
29.5kΩ
3.0
5.5kΩ
7.5kΩ
13kΩ
27.3kΩ
Table 21. RSET vs. Segment Current and LED Forward Voltage, VDD = 4.0V
ISEG (mA)
1.5
VLED(V)
2.0
2.5
3.0
40
8.6kΩ
8.3kΩ
7.9kΩ
7.6kΩ
30
11.6kΩ
11.2kΩ
10.8kΩ
9.9kΩ
3.5
5.2kΩ
7.8kΩ
www.austriamicrosystems.com
Revision 2.1
12 - 19
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