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AM4378: Why is a buffer needed between AM4378BZDN and LCD (OSD070T1718-19TS) on TMDSEVM437X EVM?

Kuerbis
Expert 4145 points
Part Number: AM4378
Other Parts Discussed in Thread: TMDSEVM437X, SN74AVC8T245, SN74LVC244A,

Hi Team,

 

Why is a buffer (SN74LVC32244ZKE, SN74LVC244A and SN74AVC8T245) needed between AM4378BZDN and LCD (OSD070T1718-19TS) on TMDSEVM437X EVM?

 

Is the AM4378 drive capacity not enough?

Is it timing adjustment for SN74AVC8T245 level shift?

Is it possible to connect directly when the customer design a board?

 

Thanks and Best regards,

Kuerbis

  • 0
    TI__Expert 3310 points

    Hi Kuerbis,

    Looking at the TMDSEVM437X schematic:

    SN74AVC8T245 buffers are used to switch the DSS ("LCD_RED") Data paths between HDMI and LCD.  Similarly, the SN74LVC32244ZKE is being used to switch the "LCD_BLUE" and "LCD_GREEN" equivalents, same as with the previous buffer ICs. The SN74LVC244A is used for selecting between the LCD_PCLK, HSYNC and VSYNC as well as EN signals for HDMI and LCD respectively. If you only have an LCD display in your system you don't need them.

    In summary: the buffers as the EVM uses them are only needed in that configuration if you want to select between HDMI and LCD vs simply using one or the other. 

    Best Regards

    Andrei

  • 0 in reply to Andrei Aldea
    TI__Expert 4145 points

    Hi Andrei

     

    Thanks!

     

    Thanks and Best regards,

    Kuerbis