DLPS202A October 2020 – August 2024 TPS99000S-Q1
PRODUCTION DATA
A disconnection of the primary photodiode breaks the feedback loop used to regulate LED output. Any disconnection of this photodiode should be detected so the LEDs can be disabled.
The DLPC23xS-Q1 software and the TPS99000S-Q1 implement a photo feedback monitor Built-In Self-Test (BIST) to detect a disconnected photodiode. Every video frame, the DLPC23xS-Q1 software uses ADC measurements of the LED current and TIA output, and COMPOUT falling edges to detect a disconnected photodiode.
In continuous mode, the DLPC23xS-Q1 software determines that the photodiode is disconnected if all the LED currents are at maximum, but the TIA measurements are at a minimum. This indicates that the LEDs are conducting current, but the photodiode is not responding to light output from the LEDs.
In discontinuous mode, COMPOUT edges are used to detect a photodiode disconnect. A falling edge on COMPOUT indicates that an LED pulse has reached the desired threshold. This is only possible if the photodiode is connected. Therefore, the COMPOUT edges are detected by the DLPC23xS-Q1 software to determine if the photodiode is connected.