6

FN3159.2

February 15, 2007

Inter Digit Blanking

A blanking time of approximately 10

μs occurs between digit

strobes. This ensures that the segment information is correct

before the next digit drive, thereby avoiding display ghosting.

Driving Larger Displays

If a higher average drive current per digit is required, it is

possible to connect digit drive outputs together. For example,

by paralleling pairs of digit drivers together to drive a 4 digit

display, 5mA average segment drive current can be obtained.

Power Dissipation Considerations

with an average of 5 segments driven per digit, the average

current would be approximately 200mA. Assuming a 1.8V

drop across the LED display, there will be a 3.2V drop across

the ICM7218. The device power dissipation will therefore be

640mW, rising to about 900mW, for all ‘8’ ‘s displayed.

Caution: Position device in system such that air can

flow freely to provide maximum cooling. The common

cathode dissipation is approximately one-half that of the

common anode dissipation.

Sequential Addressing Considerations

(lCM7218A/B)

The control instructions are read from the input bus lines if

MODE is high and WRITE low. The instructions occur on 4

lines and are - DECODE/no Decode, type of Decode (if

desired), SHUTDOWN/no Shutdown and DATA COMlNG/not

Coming. After the control word has been written (with the Data

Coming instruction), display data can be written into memory

with each successive negative going WRITE pulse. After all

8-digit memory locations have been written to, additional

transitions of the WRITE input are ignored until a new control

word is written. It is not possible to change one individual digit

without refreshing the data for all the other digits.

Random Access Input Drive Considerations

(ICM7218C/D)

Control instructions are provided to the ICM7218C/D by a

single three level input terminal (Pin 9), which operates

independently of the WRITE pulse.

Data can be written into memory on the lCM7218C/D by

setting up a 3 bit binary code (one of eight) on the digit

address inputs and applying a low level to the WRITE pin.

For example, it is possible to change only digit 7 without

altering the data for the other digits. (See Figure 6).

Supply Capacitor

A 0.1

μF plus a 47μF capacitor is recommended between

FIGURE 4. TIMING DIAGRAM FOR ICM7218A/B

FIGURE 5. LOAD SEQUENCE ICM7218A/B

ICM7218