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:
Equation 1. TARRAY = TCERAMIC + (QARRAY ×
RARRAY-TO-CERAMIC)
Equation 2. QARRAY = QELECTRICAL +
QILLUMINATION
where
- TARRAY = Computed array
temperature (°C)
- TCERAMIC = Measured ceramic
temperature (°C) (TP1 location)
- RARRAY-TO-CERAMIC = Thermal
resistance of package specified in Section 6.5 from array to ceramic
TP1 (°C/Watt)
- QARRAY = Total DMD power on
the array (W) (electrical + absorbed)
- QELECTRICAL = Nominal
Electrical Power (W)
- QINCIDENT = Incident
illumination optical power (W)
- QILLUMINATION = (DMD average
thermal absorptivity × QINCIDENT) (W)
- DMD average thermal absorptivity =
0.42
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 W. 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 single chip or multichip DMD system. It
assumes an illumination distribution of 83.7% on the active array, and 16.3% on the array
border.
The sample calculation for a
typical projection application is as follows:
Equation 3. QINCIDENT = 45 W
(measured)
TCERAMIC = 55.0°C
QELECTRICAL = 1.5 W
QARRAY = 1.5 W + (0.42 × 45 W) =
20.4 W
TARRAY = 55.0°C + (20.4 W × 0.50°C/W) = 65.2 °C