HCMS-3901 Datasheet, PDF (16/18 Pages) AVAGO TECHNOLOGIES LIMITED – 3.3 V High Performance CMOS 5x7 AlphaNumeric Displays

Appendix A. Thermal Considerations
The display IC has a maximum junction temperature of
150°C. The IC junction temperature can be calculated
with Equation 1 in Table 3.
A typical value for Rθ_JA is 100°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 .062 inch thick
PCB with .020-inch wide, one ounce copper traces. P_D
can be calculated as Equation 2 in Table 3.
Figure 9 shows how to derate the power of one IC
versus ambient temperature. Operation at high ambient
temperatures may require the power per IC to be
reduced. The power consumption can be reduced by
changing the N, I_PIXEL , Osc cyc or V_LED. Changing V_LOGIC
has very little impact on the power consumption.
1.3
1.2
R_θJ-A = 100°C/W
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
25 30 35 40 45 50 55 60 65 70 75 80 85 90
T_A– AMBIENT TEMPERATURE – °C
Figure 9. Maximum power dissipation per IC versus ambient temperature
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