FUNCTIONAL DESCRIPTION

digit alphanumeric displays with minimal interface

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 1. The output

current is typically 20 times greater than the current

into pin 13, which is set by an external variable

resistor.

There is an internal limiting resistor of 400

Ω nomi-

nal value.

Figure 2 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 mas-

ter-slave configurations. There is no clear for the

master portion of the first register, thus allowing

continuous operation.

36

BIT 34

BIT 35

CLOCK

DATA

LOAD

(INTERNAL)

RESET

(INTERNAL)

START

BIT 1

1

Figure 2 : Input Data Format

STATIC ELECTRICAL CHARACTERISTICS

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

Supply Voltage

4.75

13.2

V

Supply Current

7

mA

Input Voltages

Logical "0" Level

Logical "1" Level

± 10 µA Input Bias

4.75

– 0.3

2.2

0.8

V

V

V

Brightness Input Current (note 2)

0

0.75

mA

Brightness Input Voltage (pin 13)

Input Current = 750

3

4.3

V

Off State Output Voltage

13.2

18

V

Output Sink Current (note 3)

Segment OFF

Segment ON

Brightness In. = 0

µA

Brightness In. = 100

µA

Brightness In. = 750

µA

0

2

12

2.7

15

10

10

4

25

µA

µA

mA

mA

Input Clock Frequency

0

0.5

MHz

Output Matching (note 1)

± 20

%

2. With a fixed resistor on the brightness input some variation in brightness will occur from one device to another.

3. Absolute maximum for each output should be limited to 40 mA.

M5480

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