M5451B7 Datasheet, PDF (3/12 Pages) STMicroelectronics – LED DISPLAY DRIVERS

M5450, M5451
Table 1. Absolute Maximum Ratings
Symbol
Parameter
Value
Unit
V_DD
Supply Voltage
– 0.3 to 15
V
V_I
Input Voltage
– 0.3 to 15
V
V_O(off)
Off State Output Voltage
15
V
I_O
Output Sink Current
40
mA
P_TOT
Total Package Power Dissipation at 25°C
Total Package Power Dissipation at 85°C
1
W
560
mW
T_j
Junction Temperature
150
°C
T_OP
Operating Temperature Range
– 25 to 85
°C
T_STG
Storage Temperature Range
– 65 to 150
°C
Note: Stresses above those listed under "Absolute Maximum Ratings" may causes permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
FUNCTIONAL DESCRIPTION
Both the M5450 and the M5451 are specially de-
signed to operate 4 or 5-digit alphanumeric dis-
plays 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 LED displays.
A 1nF capacitor should be connected to bright-
ness control, pin 19, to prevent possible oscilla-
tions.
A block diagram is shown in Figure 3. For the
M5450 a DATA ENABLE is used instead of the
35th output. The DATA ENABLE input is a metal
option for the M5450.
The output current is typically 20 times greater
than the current into pin 19, which is set by an ex-
ternal variable resistor. There is an internal limiting
resistor of 400W 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 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 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.
Bit 1 is the first bit following the start bit and it will
appear on Pin 18. A logical "1" at the input will turn
on the appropriate LED.
Figure 5 shows the timing relationship between
Data, Clock and DATA ENABLE.
A max clock frequency of 0.5MHz 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_OUT.
The following equation can be used for calcula-
tions.
T_j = [(V_OUT) (I_LED) (No. of segments) + (V_DD ×
7mA)] (124°C/W) + T_amb
where :
T_j = junction temperature (150°C max)
V_OUT = the voltage at the LED driver outputs
I_LED = the LED current
124°C/W = thermal coefficient of the package
T_amb = ambient temperature
The above equation was used to plot Figure 6, Fig-
ure 7 and Figure 8.
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