SLLSEX2F December 2016 – April 2024 TDP158
PRODUCTION DATA
The TDP158 solves sink/source level issues by implementing a controller/target control mode for the DDC bus. When the TDP158 detects the start condition on the DDC bus from the SDA_SRC/SCL_SRC it transfers the data or clock signal to the SDA_SNK/SCL_SNK with little propagation delay. When SDA_SNK detects the feedback from the downstream device, the TDP158 pulls up or pulls down the SDA_SRC bus and delivers the signal to the source.
The DDC link defaults to 100Kbps but can be set to various values including 400Kbps by setting the correct value to address 22h through the I2C interface. The HPD goes to high impedance when VCC is under low power conditions, < 1.5V.
The TDP158 uses clock stretching for DDC transactions. As there are sources and sinks that do not perform this function correctly, a system may not work correctly as DDC transactions are incorrectly transmitted/received. To overcome this, a snoop configuration can be implemented where the SDA/SCL from the source is connected directly to the SDA/SCL pins. The TDP158 needs the SDA_SNK and SCL_SNK pins connected to the sink DDC pins so that the TMDS_CLOCK_RATIO_STATUS bit can be automatically set; otherwise, it will have to be set through I2C. For best noise immunity, the SDA_SRC and SCL_SRC pins should be connected to GND. Care must be taken when this configuration is being implemented as the voltage level for DDC between the source and sink may be different, 3.3V versus 5V.