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M5482B7
LED Display Driver
1/10June 2004
M5482LED DISPLAY DRIVER
REV. 2
FEATURES SUMMARY 2 DIGIT LED DRIVER (15 segments) CURRENT GENERATOR OUTPUTS (no
resistor required) CONTINUOUS BRIGHTNESS CONTROL SERIAL DATA INPUT WIDE SUPPLY VOLTAGE OPERATION TTL COMPATIBILITY
APPLICATION EXAMPLES MICROPROCESSOR DISPLAYS INDUSTRIAL CONTROL INDICATOR RELAY DRIVER INSTRUMENTATION READOUTS
DESCRIPTIONThe M5482 is a monolithic MOS integrated circuit
produced with an N-channel silicon gate technolo-
gy. It utilizes the M5451 die packaged in a 20-pin
plastic package copper frame, making it ideal for a
2-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.
Figure 1. Package
Figure 2. Pin Connections
M5482
Figure 3. Block Diagram
Table 1. Absolute Maximum RatingsNote: Stresses in excess of those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress
rating only and functional operation of the device at these or any other conditions in excess of those indicated in the operational sec-
tions of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reli-
ability.
3/10
M5482
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 IMAX + 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 M5482 uses the M5451 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 in 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.
There is an internal limiting resistor of 400Ω 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.
M5482
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 return the chip to its normal operation.
Figure 5 shows the timing relationships between
Data and Clock. maximum clock frequency of 0.5 MHz is as-
sumed.
Table 3 shows the Output Data Format for the
M5482. Because it uses only 15 of the possible 35
outputs, 20 of the bits 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 . 7 mA]
(80 °C/W) + Tamb
where:
Tj ≡ junction temperature (150 °C max)
VOUT = the voltage at the LED driver outputs
ILED = the LED current
80 °C/W = thermal coefficient of the package
Tamb = ambient temperature
Figure 5.
Table 3. Serial Data Bus / Outputs Correspondence
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M5482
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
----------------------- ------------------------ -----------------=
M5482
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.
