HDSP-253 Datasheet, PDF (15/16 Pages) Agilent(Hewlett-Packard) – Eight Character 5 mm Smart Alphanumeric Display

15
Table 3. Maximum Allowable Ambient Temperature for Various Operating Conditions (cont’d.)
All Colors Except AlGaAs Red
Character
Number of
Brightness
V_DD
Characters
Level
V
# (20 dots)
8
100%
5.5
# (20 dots)
8
100%
5.25
# (20 dots)
8
100%
5.0
# (20 dots)
7
100%
5.5
# (20 dots)
6
100%
5.5
# (20 dots)
8
80%
5.5
V (12 dots)
8
100%
5.5
I_DD
P_D
Rθ_J-A T_AMAX
mA
W
°C/W
°C
373
2.0
39
72
354
1.9
39
77
335
1.67
39
85
326
1.8
39
80
280
1.5
39
85
298
1.6
39
85
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.
Ground Connections
Two ground pins are provided to
keep the internal IC logic ground
clean. The designer can, when
necessary, route the analog
ground for the LED drivers
separately from the logic ground
until an appropriate ground plane
is available. On long inter-
connections between the display
and the host system, the designer
can keep voltage drops on the
analog ground from affecting the
display logic levels by isolating
the two grounds.
The logic ground should be con-
nected to the same ground poten-
tial as the logic interface circuitry.
The analog ground and the logic
ground should be connected at a
common ground which can
withstand the current induced by
the switching LED drivers.
When separate ground
connections are used, the analog
ground can vary from -0.3 V to
+0.3 V with respect to the logic
ground. Voltage below -0.3 V can
cause all dots to be on. Voltage
above +0.3 V can cause dimming
and dot mismatch.
Solder and Post Solder
Cleaning
Note: Freon vapors can cause the
black paint to peel off the display.
See Application Note 1027 for
information on soldering and post
solder cleaning.
Contrast Enhancement
(Filtering)
See Application Note 1015 for
information on contrast
enhancement.