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M5481B7
LED DISPLAY DRIVER
1/10April 2004
M5481LED DISPLAY DRIVER
REV. 2
FEATURES SUMMARY 2 DIGIT LED DRIVER (14 segments) CURRENT GENERATOR OUTPUTS (no
registor required) CONTINUOUS BRIGHTNESS CONTROL SERIAL DATA INPUT DATA ENABLE WIDE SUPPLY VOLTAGE OPERATION TLL COMPATIBILITY APPLICATION EXAMPLES MICROPROCESSOR DISPLAYS INDUSTRIAL CONTROL INDICATOR RELAY DRIVER INSTRUMENTATION READOUTS
DESCRIPTIONThe M5481 is a monolithic MOS integrated circuit
produced with a N-channel silicon gate technolo-
gy. It uses the M5450 die packaged in a 20-pin
plastic package copper frame, making it ideal for a
1-digit display. A single pin controls the LED dis-
play brightness by setting a reference current
through a variable resistor connected either to VDD
or to a separate supply of 13.2V maximum.
The M5481 is a pin-to-pin replacement of the NS
MM 5481.
Figure 1. Package
Figure 2. Pin Connections
M5481
Figure 3. Block Diagram
Table 1. Absolute Maximum RatingsNote: Stresses exceeding those listed under “Absolute Maximum Ratings” may cause permanent damage to the device and affect its reli-
ability.
3/10
M5481
Table 2. Static Electrical Characteristics
(Tamb within operating range, VDD = 4.75V to 13.2V, VSS = 0V, unless otherwise specified)Note:1. Output matching is calculated as the percent variation from I MAX + IMIN/2. With a fixed resistor on the brightness input some variation in brightness will occur from one device to another. Absolute maximum for each output should be limited to 40mA. The VO voltage should be regulated by the user.
FUNCTIONAL DESCRIPTIONThe M5481 uses the M5450 die which is packaged
to operate 2-digit alphanumeric displays with min-
imal interface with the display and the data source.
Serial data transfer from the data source to the dis-
play driver is accomplished with 2 signals, serial
data and clock. using a format of a leading “1” fol-
lowed by the 35 data bits allows data transfer with-
out 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 se-
rial 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 9) to pre-
vent possible oscillations.
A block diagram is shown on Figure 3. The output
current is typically 20 times greater than the cur-
rent into pin 9, which is set by an external variable
resistor.
The latter is an internal limiting resistor of 400Ω
nominal 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 is generated synchronously with the
high state of the clock, which loads the 35 bits of
the shift registers into the latches.
M5481
Figure 4. Input Data FormatAt 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 shift register, thus al-
lowing continuous operation.
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 reset the chip to its normal operation.
Figure 5 shows the timing relationships between
Data, Clock and DATA ENABLE.
A maximum clock frequency of 0.5MHz is as-
sumed.
Table 3 shows the Output Data Format for the
M5481. Because it uses only 14 of the possible
outputs, 21 of the bits (including bit 35 which was
already unused in the M5450) are “Don’t Cares” .
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
1V Vout.
The following equation can be used for calcula-
tions.
Tj = [(Vout) (ILED) (No. of segments) + VDD x 7mA]
x (80°C/W) + Tamb
where:
Tj = junction temperature (150°Cmax)
Vout = voltage at the LED driver outputs
ILED = LED current
80°C/W = thermal coefficient of the package
Tamb = ambiant temperature
Figure 5.
Table 3. Serial Data Bus / Outputs Correspondance
5/10
M5481
TYPICAL APPLICATION
Figure 6. BASIC electronically tuned TV system
POWER DISSIPATION OF THE ICThe power dissipation of the IC can be limited us-
ing different configurations.
Figure 7. In this application R must be chosen taking into ac-
count the worst operating conditions.
R is determined by the maximum number of seg-
ments activated.
The worst case condition for the device is when
roughly half of the maximum number of segments
are activated.
It must be checked that the total power dissipation
does not exceed the absolute maximum ratings of
the device.
In critical cases more resistors can be used in con-
junction with groups of segments.In this case the
current variation in the single resistor is reduced
and Ptot limited.C V DMAX– V OMIN– MAXLD
----------------------- ------------------------ -----------------=
M5481
Figure 8. In this configuration the drop on the serial connect-
ed diodes is quite stable if the diodes are properly
chosen.
The total power dissipation of the IC depends only,
in first approximation, on the number of segments
activated.
Figure 9. In this configuration VOUT+VD is constant. the total
power dissipation of the IC depends only on the
number of segments activated.
