HDSP-2533 Datasheet, PDF (14/15 Pages) AVAGO TECHNOLOGIES LIMITED – Eight Character 5 mm Smart Alphanumeric Display

Table 3 shows the calculated maximum allowable ambient
temperature for several differ­ent sets of operating condi-
tions. 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 tempera­ture. The
typical alpha­numeric character is 15 pixels. For conditions
not listed in Table 3, you can calculate the power dissipat-
ed by the IC and use Figure 10 to determine the maximum
ambient temperature.
2.3
AlGaAs
2.2
2.1
Rθ_J-A = 39C/W
2.0
ALL OTHER COLORS
1.9
1.8
1.7
1.6
1.5
50 55 60 65 70 75 80 85 90
TA – AMBIENT TEMPERATURE – C
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
Number of
Brightness
V_DD
I_DD
P_D
Character
Characters
Level
V
mA
W
# (20 dots)
8
100%
5.5
408
2.2
# (20 dots)
8
100%
5.25
387
2.0
# (20 dots)
8
100%
5.0
366
1.8
# (20 dots)
7
100%
5.5
357
2.0
# (20 dots)
6
100%
5.5
306
1.7
# (20 dots)
8
80%
5.5
327
1.8
# (20 dots)
8
80%
5.25
310
1.6
# (20 dots)
8
53%
5.5
216
1.2
V (12 dots)
8
100%
5.5
228
1.3
Rq_J-A
T_AMAX
°C/W
°C
39
64
39
72
39
80
39
72
39
84
39
80
39
85
39
85
39
85
Table 4. Maximum Allowable Ambient Temperature for Various Operating Conditions (cont’d.)
All Colors Except AlGaAs Red
Character
Number of
Brightness
V_DD
I_DD
Characters
Level
V
mA
P_D
Rq_J-A
T_AMAX
W
°C/W
°C
# (20 dots)
8
100%
5.5
373
2.0
39
72
# (20 dots)
8
100%
5.25
354
1.9
39
77
# (20 dots)
8
100%
5.0
335
1.67
39
85
# (20 dots)
7
100%
5.5
326
1.8
39
80
# (20 dots)
6
100%
5.5
280
1.5
39
85
# (20 dots)
8
80%
5.5
298
1.6
39
85
V (12 dots)
8
100%
5.5
207
1.1
39
85
The actual IC temperature is easy to measure. Pin 17 is thermally and electrically connected to the IC substrate. The thermal resistance from pin 17 to
the IC is 16°C/W. The procedure to measure the IC junction temperature is as follows:
1.  Measure V_DD and I_DD for the display. Measure V_DD between pins 15 and 16. Measure the current entering pin 15.
2.  Measure the temperature of pin 17 after 45 minutes. Use an electrically isolated thermal couple probe.
3.  T_J(IC) = T_pin + V_DD x I_DD x 16°C/W.
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