This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN65LV1023A: SPI periperipheral to a single LVDS differential signal

Part Number: SN65LV1023A
Other Parts Discussed in Thread: SN65LV1224B, , TIDA-060017

Hi Experts,

A customer is interested in the SN65LV1023A and SN65LV1224B pair and would like to know if there a similar chip that is offered by TI that maybe interfaces a SPI periperipheral to a single LVDS differential signal? the customer is hoping to transmit the serial data over a cable and would prefer to not send chip select, sclk, MISO and MOSI over 8 wires. Ideally just MOSI or MISO over 2 wires and have the LVDS do the PLL clock recovery.

Hoping for your help.

Regards,

Marvin

  • Marvin

    I would reference you to this app note, https://www.ti.com/lit/ug/tidued8/tidued8.pdf. Would this help the customer?

    Thanks

    David

  • Hi David,

    Thank you for the response. I will let you know if the customer has additional question.

    Regards,

    Marvin

  • Hi David,

    The customer has a follow up response.

    The customer find the Reference Design TIDA-060017. This would be suitable for the customer if he had an 8-wire transmission line.

    The challenge is to interface 10-bits in parallel at greater than or equal to the minimum reference clock speed (10 MHz) of the SN65LV1023A serializer. They don't have the bandwidth to program an FPGA and also have some concerns that 10 MHz might be too fast for bit-banging 10 GPIO. So, they are looking for an IC that allowed to use a higher speed peripheral on the microprocessor similar to below:
    uP SPI peripheral ---> pcb traces (MISO, MOSI, SCLK, !CS) ---> SPI to 10-bit parallel converter ---> pcb traces (10-bit data, refclk) -----> SN65LV1023A -----> 2-wire transmission line -----> similar on receiving end with SN65LV1224B

    Is there something we can recommend?

    Regards,

    Marvin

  • Hi Marvin,

    We do not have a SPI to 10 bit bridge. What is driving this requirement to serialize the SPI interface? Is it strictly required to go down to a 2-wire interface?  

  • Hi Malik,

    Thanks for the help. The customer asked if we can suggest an alternate solution instead of fixing the one they had.

    Here is the response from the customer:

    "Requirements:

    >Minimum 30 Mbit/s
    >Multi-drop capable
    >Low power
    >Reliable transmission over cable (100 m or longer is a stretch goal).
    >2-wire half-duplex transmission (4-wire for full-duplex is okay)
    >The PCB is very small (at least for us) so I can't have an IC much bigger than the 5x5 mm VQFN that the SN65LV1023A/1224B comes in.

    B-LVDS seemed like a logical choice over RS485. There don't seem to be many multi-drop capable PHY solutions out there. I considered multi-point with Ethernet and Single Pair Ethernet but the power cost is too high with needing a new PHY at each node of the "multi-drop". One additional design constraint is to minimize the number of wires in the cable. So I am very interested in just a 2-wire half-duplex solution. I would consider a 4-wire full-duplex solution. (Hence SPI over LVDS from Reference Design TIDA-060017 won't work).
    Previous attempts at LVDS that we have tried have bottlenecked at the microprocessor end where our UART was unable to over-sample fast enough to receive serial data greater than 10 Mbit/s. That is why the SerDes feature with the PLL clock recovery was so attractive in the SN65LV1023A/1224B. However, the 10 MHz clock minimum is a tad fast for us. We don't have 10 UARTs so we have to bit-bang the 10 GPIO manually which is not impossible, but challenging. 10 bits at 10 Mb/s is 100Mb/s which is three times faster than what we need. If there was a different SerDes - LVDS IC that could accept something like a 3 MHz clock and 10-bits in parallel to give us the 30 Mbit/s we need, that could work."

    Let me know if you need more information.

    Thank you and stay safe.

    Regards,

    Marvin 

  • Hi Marvin,

    It seems your customer should look into implementing CAN bus or Ethernet connection. LVDS does not have the reach (100m) at the speeds (30Mbit/s) desired. Also we do not have a SERDES that fit well for this application.

    https://www.ti.com/lit/an/sloa101b/sloa101b.pdf CAN Bus intro

    https://www.ti.com/lit/an/slaa844/slaa844.pdf LVDS How Far How Fast

    https://www.ti.com/lit/an/slaa845/slaa845.pdf M-LVDS How Far How Fast