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M5480B7
LED DISPLAY DRIVER
1/10April 2004
M5480LED DISPLAY DRIVER
REV. 2
FEATURES SUMMARY 3 1/2 DIGIT LED DRIVER (23 segments) CURRENT GENERATOR OUTPUTS (no
resistors required) CONTINUOUS BRIGHTNESS CONTROL SERIAL DATA INPUT NO LOAD SIGNAL REQUIRED WIDE SUPPLY VOLTAGE OPERATION TTL COMPATIBILITY
Application Examples: MICROPROCESSOR DISPLAY INDUSTRIAL CONTROL INDICATION RELAY DRIVER INSTRUMENTATION READOUTS
DESCRIPTIONThe M5480 is a monolithic MOS integrated circuit
produced with a N-channel silicon gate technolo-
gy. It utilizes the M5451 die packaged in a 28-pin
plastic package making it ideal for a 3 1/2 digit dis-
paly. A single pin controls the LED dispaly bright-
ness by setting a reference current through a
variable resistor connected either to VDD or to a
separate supply of 13.2V maximum.
The M5480 is a pin-to-pin replacement of the NS
MM 5480.
Figure 1. Package
M5480
Figure 2. Pin Connections
Figure 3. Block Diagram
3/10
M5480
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.
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.
M5480
FUNCTIONAL DESCRIPTIONThe 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 FormatThere 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
1V VOUT.
The following equation can be used for calcula-
tions.
Tj = [ (VOUT) (ILED) (No.of segments) + VDD . 7 mA]
(132 °C/W) + Tamb
where:
Tj = junction temperature (150 °C max)
VOUT = the voltage at the LED driver outputs
ILED = the LED current
132 °C/W = thermal coefficient of the package
Tamb = ambient temperature
5/10
M5480
Figure 5.
Table 3. Serial Data Bus / Outputs Correspondance
TYPICAL APPLICATION
Figure 6. Basic 3 1/2 Digit Interface
M5480
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 resis-
tor is reduced and Ptot limited.
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, in a
first approximation, only on the number of seg-
ments activated.
Figure 9. In this configuration VOUT + VD is constant. The to-
tal power dissipation of the IC depends only on the
number of segments activated.C V DMAX– V OMIN– MAXLD
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