Figure 7-2 DMD Thermal Test Points

Micromirror array temperature can be computed analytically from measurement points on the outside of the package, the package thermal resistance, the electrical power, and the illumination heat load. The relationship between micromirror array temperature and the reference ceramic temperature is provided by the following equations:

where

• T_ARRAY = computed array temperature (°C)
• T_CERAMIC = measured ceramic temperature (°C) (TP1 location)
• R_{ARRAY-TO-CERAMIC} = thermal resistance of package from array to ceramic TP1 (°C/Watt)
• Q_ARRAY = Total DMD power on the array (Watts) (electrical + absorbed)
• Q_ELECTRICAL = nominal electrical power
• Q_ILLUMINATION = (C_L2W × SL)
• C_L2W = Conversion constant for screen lumens to power on DMD (Watts/Lumen)
• SL = measured screen lumens

The electrical power dissipation of the DMD is variable and depends on the voltages, data rates and operating frequencies. A nominal electrical power dissipation to use when calculating array temperature is 0.9 Watts. The absorbed power from the illumination source is variable and depends on the operating state of the micromirrors and the intensity of the light source. The equations shown above are valid for a 1-Chip DMD system with projection efficiency from the DMD to the screen of 87%.

The conversion constant CL2W is based on array characteristics. It assumes a spectral efficiency of 300 lumens/Watt for the projected light and illumination distribution of 83.7% on the active array, and 16.3% on the array border.

Sample calculations for typical projection application: