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TCA9509: Right part selection

Hideki Hayashi1
Expert 8480 points
Part Number: TCA9509
Other Parts Discussed in Thread: TMDS1204,

Tool/software:

Hi team,

Customer is looking for level shifter for HDMI clock (LV_DDC_SCL/SDA to DDC_SCL/SDA), which is required for source application with TMDS1204.

The host (A-side): VIO=1.8V and VOL(max) is 0.45V.

HDMI connector (B-side): VIO=5V, HDMI compliance must be followed and it specs "below 0.4V". So VOL(max) of level shifter must be <0.4V.

Do we have solutions?

Regards,

Hayashi

  • 0
    TI__Mastermind 49768 points

    Hayashi,

    The VOL is determined by the PU resistors on both sides of the level shifter. 

    I2C Bus Pullup Resistor Calculation Application Note

    VIL for the 1.8V device is VIL = 0.3 x 1.8 = 0.54V. 

    The maximum VOL from the 5V device is < 0.4V. I don't think we need a buffer here like the TCA9509. 

    Can we use a cheap level shifter here like LSF0102 or TCA39306? 

    Regards,

    Tyler

  • 0
    Guru 317480 points

    The HDMI DDC specification requires pull-ups between 1.5 kΩ and 2 kΩ on the source side (and a 47 kΩ ±10 % pull-up on the sink's SCL). And it is not really possible to control the total bus capacitance, so it looks as if the GPU's output pins will not be able to drive the entire bus, and a buffer is necessary.

    As far as I can see, the TCA9509 should work as long as the pull-ups on the 1.8 V bus are large enough to restrict VOL to at most 0.11 V. So assuming that the GPU's VOL(max) is specified for a load of 3 mA, the pull-ups on LV_DDC_SCL/SDA must be at least 2.7 kΩ.