HDSP-253 Datasheet, PDF (14/16 Pages) Agilent(Hewlett-Packard) – Eight Character 5 mm Smart Alphanumeric Display

14
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.
Table 3 shows the calculated
maximum allowable ambient
temperature for several different
sets of operating conditions. The
worst case alphanumeric
characters (#,@,B) have 20
pixels. Displaying eight 20-pixel
characters will not occur in
normal operation. Thus, using
eight 20-pixel characters to
calculate power dissipation will
over estimate the power and the
IC junction temperature. The
average number of pixels per
character, supply voltage,
brightness level, and number of
characters are needed to calculate
the power dissipated by the IC.
The ambient temperature, power
dissipated by the IC, and the
thermal resistance are then used
to calculate IC junction tempera-
ture. The typical alphanumeric
character is 15 pixels. For
conditions not listed in Table 3,
you can calculate the power
dissipated by the IC and use
Figure 10 to determine the
maximum ambient temperature.
Figure 10. Maximum Allowable
Power Dissipation vs. Ambient
Temperature. T_JMAX = 150 °C or
120°C.
Table 3. Maximum Allowable Ambient Temperature for Various Operating Conditions
AlGaAs Red
Character
# (20 dots)
Number of
Brightness
V_DD
Characters
Level
V
8
100%
5.5
I_DD
P_D
Rθ_J-A
mA
W
°C/W
408
2.2
39
# (20 dots)
8
100%
5.25
387
2.0
39
# (20 dots)
8
100%
5.0
366
1.8
39
# (20 dots)
7
100%
5.5
357
2.0
39
# (20 dots)
6
100%
5.5
306
1.7
39
# (20 dots)
8
80%
5.5
327
1.8
39
# (20 dots)
8
80%
5.25
310
1.6
39
# (20 dots)
8
53%
5.5
216
1.2
39
V (12 dots)
8
100%
5.5
228
1.3
39
T_AMAX
°C
64
72
80
72
84
80
85
85
85