7228AIBIZ 查看數據表（PDF） - Renesas Electronics

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7228AIBIZ

8-Digit, Microprocessor-Compatible, LED Display Decoder Driver

Renesas Electronics 

ICM7228

The ICM7228 operating current with the display blanked is

within 100A - 200A for all versions. All versions of the

ICM7228 can be blanked by writing Hex FF to all digits and

selecting Code B format. The ICM7228A and ICM7228B can

also be blanked by selecting No Decode mode and writing Hex

80 to all digits (See Tables 5and 6).

Common Anode Display Drivers, ICM7228A and

ICM7228C

The common anode digit and segment driver output schematics

are shown in Figure 12. The common anode digit driver output

impedance is approximately 4. This provides a nearly constant

voltage to the display digits. Each digit has a minimum of 200mA

drive capability. The N-Channel segment driver’s output

impedance of 50 limits the segment current to approximately

25mA peak current per segment. Both the segment and digit

outputs can directly drive the display, current limiting resistors

are not required.

Individual segment current is not significantly affected by whether

other segments are on or off. This is because the segment driver

output impedance is much higher than that of the digit driver. This

feature is important in bar graph applications where each bar

graph element should have the same brightness, independent of

the number of elements being turned on.

Common Cathode Display Driver, ICM7228B

The common cathode digit and segment driver output

schematics are shown in Figure 13. The N-channel digit drivers

have an output impedance of approximately 15. Each digit

has a minimum of 50mA drive capability. The segment drivers

have an output impedance of approximately 100 with

typically 10mA peak current drive for each segment. The

common cathode display driver output currents are only 1/4 of

the common anode display driver currents. Therefore, the

ICM7228A and ICM7228C common anode display drivers are

recommended for those applications where high display

brightness is desired. The ICM7228B common cathode display

driver is suitable for driving bubble-lensed monolithic 7

segment displays. They can also drive individual LED displays

up to 0.3 inches in height when high brightness is not required.

Display Multiplexing

Each digit of the ICM7228 is on for approximately 320s, with

a multiplexing frequency of approximately 390Hz. The

ICM7228 display drivers provide interdigit blanking. This

ensures that the segment information of the previous digit is

gone and the information of the next digit is stable before the

next digit is driven on. This is necessary to eliminate display

ghosting (a faint display of data from previous digit

superimposed on the next digit). The interdigit blanking time is

10s typical with a guaranteed 2s minimum. The ICM7228

turns off both the digit drivers and the segment drivers during

the interdigit blanking period. The digit multiplexing sequence

is: D2, D5, D1, D7, D8, D6, D4 and D3. A typical digit’s drive

pulses are shown on Figure 4.

Due to the display multiplexing, the driving duty cycle for each

digit is 12% (100 x 1/8) This means the average current for

each segment is 1/8 of its peak current. This must be

considered while designing and selecting the displays.

Driving Larger Displays

If very high display brightness is desired, the ICM7228 display

driver outputs can be externally buffered. Figures 14 thru 16

show how to drive either common anode or common cathode

displays using the ICM7228 and external driver circuit for

higher current displays.

Another method of increasing display currents is to connect

two digit outputs together and load the same data into both

digits. This drives the display with the same peak current, but

the average current doubles because each digit of the display

is on for twice as long, i.e., 1/4 duty cycle versus 1/8.

DIGIT

STROBE

INTERDIGIT

BLANKING

VDD

P

200mA

SHUTDOWN

COMMON

ANODE

N

N

N

DIGIT

2k OUTPUT

VSS

N

2k

VSS

NOTE: When SHUTDOWN goes low INTERDIGIT BLANKING also

stays low.

FIGURE 12A. DIGIT DRIVER

SEGMENT

DATA

INTERDIGIT

BLANKING

SHUTDOWN

VDD

P

2k

COMMON

ANODE

N

SEGMENT

75 OUTPUT

VSS

FIGURE 12B. SEGMENT DRIVER

FIGURE 12. COMMON ANODE DISPLAY DRIVERS

FN3160 Rev 9.00

August 19, 2015

Page 14 of 19

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