DLPU094 July   2020 DLP5530S-Q1

 

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7.3.2.2.2 LED Control Feedback Loop Protection

The following methods are used to monitor and diagnose the control the LED control and feedback loop:

  • [SM_21] DAC to ADC Loopback Test: Checks that the ADCs and DACs used to regulated LED brightness and current limit are functioning properly. Sets DAC levels and then measures the output of the DAC via ADC. If the ADC measurements do not match the expected DAC levels, the test fails. This test can be configured to run at start-up and it can be executed by command after the software is changed to Stand-by mode via host command. Upon failure, software will not transition to Display Mode even if it is commanded by the host. An error will also be logged.
  • [SM_22] Photo Feedback Monitor: Checks the connection of the photodiode used to regulate LED brightness. The disconnection of the photodiode could result in a very bright image. The DLP5530S-Q1 chipset has two modes of operation—continuous mode for high brightness and discontinuous mode for mid and low brightness. In continuous mode, this test compares the output of the photodiode amplifier vs. the LED current. A high LED current and low photodiode reading on for all LEDs indicates that the photodiode is disconnected. In discontinuous mode, LED current measurements are not possible, so a different method is used. The COMPOUT signal indicates whether the photodiode measurement is below or above the target brightness level of the LEDs. If the photodiode measurement never reaches the target LED brightness for all LEDs in one frame, the photodiode is considered disconnected. To prevent false failures, the number of consecutive frames that the error must persist for it to be considered a real failure is configurable in flash. The number of frames can be increased for preventing false failures. However, the number of frames needed to indicate an error and respond to it should be less than the Fault Tolerant Time Interval (FTTI) specified by the OEM. Upon failure, emergency shutdown will be executed and an error will be logged. This test is always executed during display mode.
  • [SM_6] Back End Functional Test (BEFT): Tests the sequencer block by executing a specialized LED sequence, but without turning on LEDs. Tests the sequencer block's ability to access and execute commands from sequencer memory. Makes sure that the sequencer can properly control LED illumination signals in continuous and discontinuous mode. This test can be configured to run at start-up, and it can be executed by command after the software is changed to Stand-by mode via host command. In case of test failure, software will not transition to Display Mode even if it is commanded by the host. An error will also be logged.