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DLP4710

DLPS125 – NOVEMBER 2018

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Copyright © 2018, Texas Instruments Incorporated

Micromirror Array Temperature Calculation (continued)

•

SL = Measured ANSI screen lumens (lm)

(3)

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 0.25W.

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 CL2W is based on the DMD micromirror array characteristics. It assumes a spectral

efficiency of 300 lm/W 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. The conversion constant is calculated to be 0.00266

W/lm.

Sample Calculation for typical projection application:

limits.

2. SL = 1500 lm

4. CL2W = 0.00266 W/lm

7.7 Micromirror Landed-On/Landed-Off Duty Cycle

7.7.1 Definition of Micromirror Landed-On/Landed-Off Duty Cycle

The micromirror landed-on/landed-off duty cycle (landed duty cycle) denotes the amount of time (as a

percentage) that an individual micromirror is landed in the ON state versus the amount of time the same

micromirror is landed in the OFF state.

As an example, a landed duty cycle of 75/25 indicates that the referenced pixel is in the ON state 75% of the

time and in the OFF state 25% of the time, whereas 25/75 would indicate that the pixel is in the ON state 25% of

the time. Likewise, 50/50 indicates that the pixel is ON 50% of the time and OFF 50% of the time.

Note that when assessing landed duty cycle, the time spent switching from one state (ON or OFF) to the other

state (OFF or ON) is considered negligible and is thus ignored.

Since a micromirror can only be landed in one state or the other (ON or OFF), the two numbers (percentages)

nominally add to 100.

7.7.2 Landed Duty Cycle and Useful Life of the DMD

Knowing the long-term average landed duty cycle (of the end product or application) is important because

subjecting all (or a portion) of the DMD’s micromirror array (also called the active array) to an asymmetric landed

duty cycle for a prolonged period of time can reduce the DMD’s usable life.

Note that it is the symmetry/asymmetry of the landed duty cycle that is of relevance. The symmetry of the landed

duty cycle is determined by how close the two numbers (percentages) are to being equal. For example, a landed

duty cycle of 50/50 is perfectly symmetrical whereas a landed duty cycle of 100/0 or 0/100 is perfectly

asymmetrical.

7.7.3 Landed Duty Cycle and Operational DMD Temperature

Operational DMD Temperature and Landed Duty Cycle interact to affect the DMD’s usable life, and this

interaction can be exploited to reduce the impact that an asymmetrical Landed Duty Cycle has on the DMD’s

usable life. This is quantified in the de-rating curve shown in Figure 1. The importance of this curve is that:

•

All points along this curve represent the same usable life.

•

All points above this curve represent lower usable life (and the further away from the curve, the lower the

usable life).