M5480

4/10

FUNCTIONAL DESCRIPTION

The M5480 is specifically designed to operate 31/

2 digit alphanumeric displays with minimal inter-

face with the display and the data source. Serial

data transfer from the data source to the display

driver is accomplished with 2 signals, serial data

and clock. Using a format of a leading "1" followed

by the 35 data bits allows data transfer without an

additional load signal. The 35 data bits are latched

after the 36th bit is complete, thus providing non-

multiplexed, direct drive to the display.

Outputs change only if the serial data bits differ

from the previous time.

Display brightness is determined by control of the

output current for LED displays. A 1nF capacitor

should be connected to brightness control, pin 13,

to prevent possible oscillations.

A block diagram is shown in Figure 3. The output

current is typically 20 times greater than the cur-

rent into pin 13, which is set by an external vari-

able resistor.

There is an internal limiting resistor of 400

Ω nom-

inal value.

Figure 4 shows the input data format. A start bit of

logical "1" precedes the 35 bits of data. At the 36th

clock a LOAD signal is generated synchronously

with the high state of the clock, which loads the 35

bits of the shift registers into the latches.

At the low state of the clock a RESET signal is

generated which clears all the shift registers for

the next set of data. The shift registers are static

master-slave configurations. There is no clear for

the master portion of the first register, thus allow-

ing continuous operation.

Figure 4. Input Data Format

There must be a complete set of 36 clocks or the

shift registers will not clear.

When power is first applied to the chip an internal

power ON reset signal is generated which resets

all registers and all latches. The START bit and the

first clock return the chip to its normal operation.

Figure 5 shows the timing relationships between

Data, and Clock. A maximum clock frequency of

0.5MHz is assumed.

Table 3 shows the Output Data Format for the

M5480. Because it uses only 23 of the possible 35

outputs, 12 of the bits are "Don’t Care".

For applications where a lesser number of outputs

are used, it is possible to either increase the cur-

rent per output, or operate the part at higher than

The following equation can be used for calcula-

tions.

where:

132 °C/W = thermal coefficient of the package

36

BIT 34

BIT 35

CLOCK

DATA

LOAD

(INTERNAL)

RESET

(INTERNAL)

START

BIT 1

1