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AS1105

Datasheet - Application In form atio n

9 Application Information

9.1 Supply Bypassing and Wiring

In order to achieve optimal performance the AS1105 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.

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 12. The maximum current the AS1105 can drive is 40mA. If higher currents are needed, external drivers must

be used. In that case it is no longer necessary that the AS1105 drives high currents. A recommended value for RSET is 47k

Ω. In cases that the

AS1105 only drives few digits Table 10 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 4x8 LED Dot Matrix Driver

The example in Figure 7 uses the AS1105 to drive an 4x8 LED dot matrix. The LED columns have common cathode and are connected to the

DIG0-3 outputs. The rows are connected to the segment drivers. Each of the 32 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 7. The single LEDs

in a column can be addressed as stated in Table 10, where D0 corresponds to segment G and D7 to segment DP. For a multiple digit dot matrix

several AS1105 have to be cascaded.

Figure 7. Application Example as LED Dot Matrix Driver

SEG F

SEG G

SEG E

SEG D

SEG C

SEG B

SEG A

SEG DP

DIG 0

DIG 3

4x8 LED Dot

SEG A-G DIG 0-3

18

19

VBAT

9.53k

DIN

LOA

CLK

GND

GND

ISET

VDD

DOUT

1

12

9

1

SEG F

SEG G

SEG E

SEG D

SEG C

SEG B

SEG A

SEG DP

DIG 0

DIG 3

4x8 LED Dot

SEG A-G DIG 0-3

18

19

VBAT

9.53k

DIN

LOA

CLK

GND

GND

ISET

VDD

DOUT

1

12

9

1

µP

Diode Arrangement

AS1105

AS1105