7.7.2 Sample Calculation 2: Partial DMD Active Array Illumination with Non-uniform Illumination Peak
This calculation assumes that only a subsection of the DMD active array 960 × 475 pixels in size is (non-uniformly) illuminated. This calculation assumes the illuminated area is in the center of the DMD. Non-centered area can affect the value of RSILICON-TO-CERAMIC. If the application requires offsetting the illumination on the DMD, contact TI for more information on how to assess RSILICON-TO-CERAMIC. As in Sample Calculation 1, the off-state fill factor can be used to assess the highest temperatures that can occur. Calculate the mirror temperatures which occur at the highest illumination intensities to assess the viability of the illumination conditions.
- FFOFF-STATE-MIRROR = 75.3%
- MR @ 1064 nm = 94%
- αWINDOW@ 1064 nm = 0.7%
- RMIRROR-TO-SILICON = 3.39E5 °C/Watt
- RSILICON-TO-CERAMIC = 0.9 °C/Watt (higher than previous example due to reduced illumination area)
- Pixel Size = 10.8 µm = 0.00108 cm (square)
- TCERAMIC = 30.0°C (measured)
- QINCIDENT = 60 W (measured)
- QELECTRICAL = 1.8 W
- Peak Irradiance = 500 W/cm2 (measured)
αDMD = [0.753 × (1 - 0.94)] + (1 - 0.753) + (2 × 0.007) = 0.31
QSILICON = 1.8 W + (0.31 × 60 W) =20.4 W
QINCIDENT_MIRROR = Peak Irradiance (W/cm2) × Pixel Area (cm2) = [500 W/cm2 × (0.00108 cm)2 ] = 5.832E-4 W
QMIRROR = 5.832E-4 W × 0.753 × (1 - 0.94) = 2.64E-5 W
Delta_TSILICON-TO-CERAMIC = 20.4 W × 0.9°C/W = 18.4°C
Delta_TMIRROR-TO-SILICON = 2.64E-5 W × 3.39E5°C/W= 8.9°C
TMIRROR = 30.0°C + 18.4°C + 8.9°C = 57.3°C