AS1100PL datasheet(11/17 Pages) AMSCO

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AS1100

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

9 Application Information

Supply Bypassing and Wiring

In order to achieve optimal performance the AS1100 shall be placed very close to the LED display to minimize effects

of electromagnetic interference and wiring inductance. Furthermore, it is recommended to connect a 10µF electrolytic

and a 0.1µF ceramic capacitor between VDD and GND to avoid power supply ripple. Also, both GNDs must be

connected to ground.

Selecting RSET Resistor and Using External Drivers

The current through the segments is controlled via the external resistor RSET. Segment current is about 100 times the

current in ISET. The right values for ISET are given in Table 15. The maximum current the AS1100 can drive is 40mA.

If higher currents are needed, external drivers must be used. In that case it is no longer necessary that the AS1100

drives high currents. A recommended value for RSET is 47k

Ω. In cases that the AS1100 only drives few digits, Table 12

specifies the maximum currents and RSET must be set accordingly. Refer to absolute maximum ratings to calculate

acceptable limits for ambient temperature, segment current, and the LED forward-voltage drop.

8x8 LED Dot Matrix Driver

The example in Figure 7 uses the AS1100 to drive an 8x8 LED dot matrix. The LED columns have common cathode

and are connected to the DIG0-7 outputs. The rows are connected to the segment drivers. Each of the 64 LEDs can be

addressed separately. The columns are selected via the digits as shown in Table 5. The decode mode register (0xX9)

has to be programmed to ‘00000000’ as stated in Table 4. The single LEDs in a column can be addressed as stated in

Table 9, where D0 corresponds to segment G and d/ to segment DP. For a multiple digit dot matrix several AS1100

have to be cascaded.

Table 15. RSET vs segment current and LED forward voltage

ISEG (mA)

VLED(V)

1.5

2.0

2.5

3.0

3.5

12.2k

11.8k

11.0k

10.6k

9.69k

17.8k

17.1k

15.8k

15.0k

14.0k

29.8k

28.0k

25.9k

24.5k

22.6k

66.7k

63.7k

59.3k

55.4k

51.2k

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