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DS92LV2421: about review the sch for DS92LV2421

Vera Mao
Expert 5065 points
Part Number: DS92LV2421
Other Parts Discussed in Thread: DS92LV2422,

hi dear supporting team,

my customer  is using DS92LV2421 and DS92LV2422 to transmit  2.78M LCD signal and other low speed control signal over  6m twist cable, below is their sch,   could you help check whether anything wrong? the main questions are list as below:Tks a lot!

1、for 6m distance, besides LCD signal, they also conduct bluetooth IIS, serial port signal, and some normal low speed control signal(code switch), is it ok?

 2、there are several IO port of 2421/2422 are not used, is it ok to float it? Could 2422 clkout be float?  
3、how to config BISTEN、RFB、config、IDx？
4、LCD is running at around 2.8Mhz, couold they use 50M CLOCKin？
5、are these two chips close to EOL?

  • 0
    TI__Mastermind 29655 points

    Hi Vera,

    I reviewed the schematic, and my biggest questions are related to the choice of a crystal for CLKIN instead of a synchronous CLK signal from the LCD panel. Please see responses below, especially for Question #4.

    Please see answers below:

    1. What kind of cable is it, and how good is the isolation between different signals in the cable? If the cable is simply twisted-pair, it may be challenging to send the signals over long distances unless the cable is shielded to lower the risk of cross-talk. However, since the signals are operating at relatively low frequency, I think you may be able to work with 6m.

    2. If the IO ports are unused, please check the datasheet to determine whether the default operation when the pin is floating is still acceptable. Usually, the operation when IO ports are unconnected is pull-down by default. Why would you want to float CLKOUT? The purpose of these devices is to strobe input data with CLKIN on the DS92LV2421 side, then strobe output data with CLKOUT on the DS92LV2422 side. I would investigate the purpose behind not using CLKOUT, as this request is not typical.

    3. BISTEN should be tied low (or left floating) at power-up to disable BIST for normal operation. RFB for the DS92LV2421 should be set depending on whether the incoming data is strobed on the rising or falling edge of CLKIN. The same concept applies to RFB for the DS92LV2422. Lastly, CONFIG[1:0] can be set either to '00' or '01,' since the customer is not using the CI[3:1] signals. ID[x] depends on whether SMBus communication is being used. Since I do not see SDA/SCL connected in the schematic, this pin can be left floating. 

    4. I do not think a 50-MHz clock can be used. Sometimes, if the incoming data rate is lower than the supported clock rate for these devices, customers will oversample the incoming data at a harmonic of the pixel clock so that the CLKIN rate is within the device operating range. If the incoming signals are arriving at 2.78 Mbps, then you will need to use a clock that is a harmonic, such as 2.78 x 4 = 11.12 MHz. Also, this clock should be synchronous with the data. I am concerned about using a crystal to connect to CLKIN in the schematic, as this is not synchronous with the incoming LCD data.

    5. There are no plans to EOL these devices.

    Regards,

    Michael