• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 46 subscribers
  • Views 281 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

TLC2578: CS Signal

Kaushik Prajapati
Intellectual 360 points
Part Number: TLC2574
Other Parts Discussed in Thread: TLC2578, ADC128S102

Tool/software:

Hello,

I have my ADC and Controller both on different PCBs.

ADC is on High Voltage Section(36KV) so to isolate I wanted to use Fiber Optic links to communicate with ADC.

Limitation of Fiber Optic links is, they are unipolar in nature. Protocols like I2C need bidirectional communication so it seems SPI is the only option.

I have another limitation I can't use 4 Fiber Optic links for CLK, CS, SDO and SDI in SPI comm. I have a limitation of 3.

In TLC2574 / 8 it is mentioned user can tie CS to permanently low, that leaves my Fiber Optic connector requirement to 3 (Two transmitters for SCLK and SDI and one receiver for SDO at Controller end).

Is it the correct way?

Any other suggestions or devices?   My requirement is minimum 200ksps, 12bit, 4 channel or 8 channel.

Thanks,

  • 0
    Intellectual 360 points

    Part Number: TLC2574

    Tool/software:

    Hello,

    I have my ADC and Controller both on different PCBs.

    ADC is on High Voltage Section(36KV) so to isolate I wanted to use Fiber Optic links to communicate with ADC.

    Limitation of Fiber Optic links is, they are unipolar in nature. Protocols like I2C need bidirectional communication so it seems SPI is the only option.

    I have another limitation I can't use 4 Fiber Optic links for CLK, CS, SDO and SDI in SPI comm. I have a limitation of 3.

    In TLC2574 it is mentioned user can tie CS to permanently low, that leaves my Fiber Optic connector requirement to 3 (Two transmitters for SCLK and SDI and one receiver for SDO at Controller end).

    Is it the correct way?

    Any other suggestions or devices?   My requirement is minimum 200ksps, 12bit, 4 channel or 8 channel.

    Thanks,

  • +1
    TI__Genius 15150 points

    Hi Kaushik,

    Apologies for not getting to the previous post earlier. I've gone ahead and deleted it so we can stay on only one thread. 

    Unfortunately, the TLC2578 won't seem to work in your case with only 3 SPI lines, even if CS is tied permanently low. Either CS or FS needs to be actively controlled. There is the option of tying SDI to AVDD, but this won't allow you to cycle through the ADC channels. 

    I have looked for other devices that might serve your case, but they all run into the same issue. SDO (MISO) is of course needed to send conversion data to your controller, as is SCLK to synchronize the stream of data. SDI from my experience is always needed in multichannel devices as a means to select channels. Other devices, such as the ADC128S102 could operate with CS low, but it would need at least one falling edge of CS to initiate conversion. If there is a way to provide this outside of the controller, this could be a reasonable choice.

    Could I inquire more as to why there is a 3 fiber optic link limitation?

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Intellectual 360 points

    Thank you sir for your valuable reply.

    Yes sir limitation of 3 FO links is because we already have a control board with 2 Tx and 1 Rx.

    Well, in this case we will use UART instead of SPI ADC, Standard Modbus communication will serve us best because still the landing card is not designed.

    Thanks,