MM5481N National Semiconductor, MM5481N Datasheet - Page 3

• Manufacturer Part Number: MM5481N
• Description: IC LED DISPLAY DRIVER 20DIP
• Manufacturer: National Semiconductor

Specifications of MM5481N

• Display Type: LED
• Interface: Serial
• Digits Or Characters: 2 Digits
• Current - Supply: 7mA
• Voltage - Supply: 4.75 V ~ 11 V
• Operating Temperature: -25°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 20-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Configuration: -
• Other names: *MM5481N

Figure 4 shows the input data format A start bit of logical
Functional Description
The MM5481 uses the MM5450 die which is packaged to
operate 2-digit alphanumeric displays with minimal interfer-
ence to 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 0 001 F capacitor should be connected to
brightness control pin 9 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 9 which
is set by an external variable resistor There is an internal
limiting resistor of 400
‘‘1’’ precedes the 35 bits of data At the positive-going-edge
of 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 a
static master-slave configuration There is no clear for the
master portion of the first shift register thus allowing conti-
nous operation
There must be a complete set of 36 clocks (high low edges)
or the shift registers will not clear
nominal value
FIGURE 4 Input Data Format
FIGURE 3 Timing
3
Figure 5 shows the Output Data Format for the MM5481
Figure 3 shows the timing relationships between data
Data Enable
This active low signal enables the data input pin If high the
shift register sees zeroes clocked in
To blank the display at any time (i e power on) clock in 36
or more zeroes followed by a ‘one’ (start bit) followed by
36 or more zeroes
Because it uses only 14 of the possible 34 outputs 20 of the
bits are ‘Don’t Cares’ Note that only alternate groups of 4
outputs are used
clock and data enable A maximum clock frequency of
0 5 MHz is assumed
For applications where a lesser number of outputs are used
it is possible to either increase the current per output or
operate the part at higher than 1V V
equation can be used for calculations
T
where
j
T
V
I
T
e
LED
j
JA
A
JA
JA
OUT
e
(V
e
(Socket Mount)
(Board Mount)
e
e
OUT
junction temperature 150 C max
ambient temperature
e
thermal coefficient of the package
the LED current
the voltage at the LED driver outputs
) (I
LED
) (No of segments) (
e
e
61 C W
67 C W
JA
OUT
)
a
The following
T
A
TL F 6139 – 3
TL F 6139 – 4