HDSP-2533 Datasheet, PDF (13/15 Pages) AVAGO TECHNOLOGIES LIMITED – Eight Character 5 mm Smart Alphanumeric Display

Figure 8. Proper method to manually insert a display.
Figure 9. Improper method to manually insert a display.
Thermal Considerations
The HDSP-253X can operate from -40°C to +85°C. The
display’s low thermal resistance allows heat to flow from
the CMOS IC to the 24 package pins. Typically, this heat
is conducted through the printed circuit board traces to
free air. For most applications, no additional heatsinking
is needed. Illuminating all 280 LEDs simultaneously at full
brightness is not recommended for continuo­us operation.
How­ever, all 280 LEDs can be illuminated simul­taneously
at full brightness for 10 seconds at 25°C as a lamp test.
The IC has a maximum allow­able junction temperature of
150°C. The IC junction tempera­ture can be calculated with
the following equation:
T_JMAX = T_A + (P_D x Rq_J-A)
T_JMAX is the maximum allow­able IC junction temperature.
T_A is the ambient temperature surrounding the display.
P_D is the power dissipated by the IC.
Rq_J-A is the thermal resistance from the IC through the
display package and printed circuit board to the ambient.
A typical value for Rq_J-A is 39°C/W. This value is typical for
a display mounted in a socket and covered with a plastic
filter. The socket is soldered to a 0.062 in. thickprinted
circuit board with 0.020 in. wide one-ounce copper
traces.
P_D can be calculated as follows:
P_D = V_DD x I_DD
V_DD is the supply voltage and I_DD is the supply current.
V_DD can vary from 4.5 V to 5.5 V.
I_DD changes with V_DD, temperature, brightness level, and
number of on-pixels.
For AlGaAs
I_DD (#) = (83.8 x V_DD -0.35 x T_J) x B x N/8
I_DD(V) = (63 x V_DD -0.79 x T_J) x B x N/8
For the other colors
I_DD (#) = (75.4 x V_DD -0.28 x T_J) x B x N/8
I_DD(V) = (54 x V_DD -0.6 x T_J) x B x N/8
I_DD (#) is the supply current using “#” as the displayed
character.
I_DD(V) is the supply current using “V” as the displayed
character.
T_J is the IC junction temperature.
B is the percent brightness level.
N is the number of characters illuminated.
Operation in high temperature ambients may require
power derating or heatsinking. Figure 10 shows how to
derate the power for an HDSP-253X. You can reduce the
power by tighter supply voltage regulation or lowering
the brightness level.
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