Figure 7-1 DMD Thermal Test Points

Micromirror array temperature cannot be measured directly, therefore it must 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 array temperature and the reference ceramic temperature (thermal test TP1 in Figure 7-1) 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 (specified in Section 6.5) from array to ceramic TP1 (°C/Watt)
• Q_ARRAY = Total DMD power (electrical + absorbed) on the array (Watts)
• Q_ELECTRICAL = Nominal Electrical Power
• 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 1.5 Watts. Absorbed optical power from the illumination source is variable and depends on the operating state of the micromirrors and the intensity of the light source. Equations shown above are valid for a 1-chip DMD system with total projection efficiency through the projection lens from DMD to the screen of 87%.

The conversion constant C_L2W is based on the DMD micromirror array characteristics. It assumes a spectral efficiency of 300 lm/Watt for the projected light and illumination distribution of 83.7% on the DMD active array, and 16.3% on the DMD array border and window aperture.

Sample Calculations: