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TXS0102: TXS0201 and HDMI

Ari Laor
Prodigy 10 points

Part Number: TXS0102

Using TXS0102DCTR for several years as our 1.8V to 5V level shifter for HDMI DDC I2C. Recent batch of 15 boards has failures on display EDID reads.  Board is intermittently misreading display EDID causing wrong resolutions or failing all together to come up.

We scope captured the I2C clock for EDID reads. It looks like the clock is bouncing on falling edges. Or getting stuck in SDA held low as hostage NACK situations.  Or we see double clocks and early ACKs. Other unpredictable states are the result. The bus locks and EDID read fails.

We think it is the edge accelerators fighting. The curiosity issue is only the recent batch we built -  previous boards  that are identical TXS0102 work fine with same displays. Why suddenly failing? Process corner changed?

Can TI assist with debug? 

  1. Confirm if TSX0102 can be used for 100khz I2C  from 1.8V CTI carrier 1.8V into TSX out to 5V HDMI DDC  extremal displays. Or is there a more appropriate part for 1.8V i2c to external HDMI 5V?
  2. It says TSX0102 is appropriate for the I2C applications, which specs upto 400pf bus standard but then I see in the schematic checklist app note “Typically, up to 70pF unless specified in data sheets.”
  3. Are the edge accelerators getting stuck for some reason on this batch of TSX0102? Some clock falls are way more pronounced spikes than others. How does the edge accelerators work?

 

 

  • 0
    TI__Guru 60111 points

    Hi Ari,

    It is not recommended to have external pullups at the outputs of the TXS, as the device already includes internal 10kohms. Furthermore, please ensure that the trace lengths/ output capacitive load is kept as small as possible (ideally <70pF) to ensure proper functioning of the one-shot systems. From the waveforms provided, it seems that the blue signal is attempting to drive low, though due to the potential coupling from the transmission line, reflections are seen as new input state into the device and causing the one-shot to mistrigger. 

    1. Confirm if TSX0102 can be used for 100khz I2C  from 1.8V CTI carrier 1.8V into TSX out to 5V HDMI DDC  extremal displays. Or is there a more appropriate part for 1.8V i2c to external HDMI 5V?

    TXS0102 can be used for I2C signaling. However, if your application also requires redriving of the I2C signals, there are also I2C buffers i.e TCA9617A that can be used as well.

    2. It says TSX0102 is appropriate for the I2C applications, which specs upto 400pf bus standard but then I see in the schematic checklist app note “Typically, up to 70pF unless specified in data sheets.”

    TXS0102 is compatible with I2C signaling due to its ability to support both pen-drain/ push pull drivers. However, care should be taken to ensure proper functioning of the one-shots. 

    3.Are the edge accelerators getting stuck for some reason on this batch of TSX0102? Some clock falls are way more pronounced spikes than others. How does the edge accelerators work?

    This app note covers the application at a top level:  [FAQ] How does a monostable multivibrator (one shot) work? 

    Leveraging Edge Rate Accelerators with Auto-Sensing Level Shifters

    Regards,

    Jack