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Original question:

DS90UB947-Q1: Cable matching length between the FPD3- Pairs

DS90UB949-Q1: DDC pins pulled up to 5V?

Michael Holachek
Prodigy 50 points
Part Number: DS90UB949-Q1
Other Parts Discussed in Thread: PCA9306, LSF0102

I found the TI E2E post here that mentions the DS90UB949 supports 3.3V levels on DDC (based on VIH/VIL specs). However, I disconnected the DDC_SDA and DDC_SCL pins from my circuit and external pullups, and each pin still measures 5.0V. It appears there might be an internal chip pull up from DDC pins to RX_5V?

Can you provide any guidance on how to connect DCC_SDA and DDC_SCL when driven with 3.3V source?

  • +1
    Guru 284380 points

    The Pin Functions table says "Pullup to RX_5V with a 47-kΩ resistor". Apparently, this is not a requirement but a description.

    DDC always uses 5 V. When you have a 3.3 V source, you need to use a level shifter (e.g., LSF0102/PCA9306).