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AS1100

Datasheet - 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

9.1 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 10 F electrolytic and a 0.1 F ceramic capacitor between VDD

and GND to avoid power supply ripple. Also, both GNDs must be connected to ground.

9.2 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.

9.3 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 D7 corresponds to segment DP.

Note:

For a multiple-digit dot matrix, multiple AS1100 devices must be cascaded.

Figure 7. Application Example as LED Dot Matrix Driver

Table 15. RSET vs. Segment Current and LED Forward Voltage

ISEG (mA)

VLED(V)

1.5

2.0

2.5

3.0

3.5

40

12.2k

Ω

11.8k

Ω

11.0k

Ω

10.6k

Ω

9.69k

Ω

30

17.8k

Ω

17.1k

Ω

15.8k

Ω

15.0k

Ω

14.0k

Ω

20

29.8k

Ω

28.0k

Ω

25.9k

Ω

24.5k

Ω

22.6k

Ω

10

66.7k

Ω

63.7k

Ω

59.3k

Ω

55.4k

Ω

51.2k

Ω

SEG G

SEG F

SEG E

SEG D

SEG C

SEG B

SEG A

SEG DP

DIG 0

DIG 7

1

12

13

9

24

19

18

9.53k

Ω

4

SEG A:G

SEG DP

DIG0:7

DIN

LOAD

CLK

GND

GND

VDD

ISET

SEG G

SEG F

SEG E

SEG D

SEG C

SEG B

SEG A

SEG DP

DIG 0

DIG 7

1

12

13

9

19

18

9.53k

Ω

4

DIN

LOAD

CLK

GND

GND

VDD

ISET

P

AS1100

AS1100

DOUT

SEG A:G

SEG DP

DIG0:7