JAJSFO6F December 2015 – April 2019 TPS99000-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 that the LEDs can be disabled.
The DLPC230-Q1 software and the TPS99000-Q1 implement a photo feedback monitor Built-In Self-Test (BIST) to detect a disconnected photodiode. Every video frame, the DLPC230-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 DLPC230-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 DLPC230-Q1 software to determine if the photodiode is connected.