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AS1100
Datasheet - Application Information
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 mnimze effects of electromagnetic
interference and wiring inductance. Furthermore, it is recommended to connect a 10μF electrolytic and a 0.1μF ceramc capacitor between V
DD
and GND to avoid power supply ripple. Also, both GNDs must be connected to ground.
9.2 Selecting R
SET
Resistor and Using External Drivers
The current through the segments is controlled via the external resistor R
SET
. Segment current is about 100 times the current in ISET. The right
values for ISET are given in
Table 15
. The maximumcurrent 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 R
SET
is 47k
Ω
. In cases that the
AS1100 only drives few digits,
Table 12
specifies the maximumcurrents and R
SET
must be set accordingly. Refer to absolute maximumratings
to calculate acceptable limts 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. R
SET
vs. Segment Current and LED Forward Voltage
I
SEG
(mA)
V
LED
(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
μP
AS1100
AS1100
DOUT
SEG A:G
SEG DP
DIG0:7