• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 46 subscribers
  • Views 717 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.

DAC8760: Questions about daisy-chain of DAC8760.

Kazuya Nakai59
Guru 21505 points
Part Number: DAC8760
Other Parts Discussed in Thread: DAC7760

Hello guys,

One of my customers uses DAC8760 for their current products with daisy-chain.

Recently they received PCN of DAC8760 and they knew that "Daisy-Chain Operation" section and Daisy-chain related section
in the previous datasheet version SBAS528C were deleted when the latest datasheet version SBAS528D was released.

At this moment, they have the following questions about daisy-chain.  Could you please give me your reply for them?

Q1. We are using DAC8760 with daisy-chain. Do we need to stop daisy-chain using for the current products?

Q2. If we continue to use DAC8760 with daisy-chain, what is problem happened?

Your reply would be much appreciated.

Best regards,

Kazuya.

 

  • 0
    TI__Guru* 97465 points

    Kazuya-san,


    First, I want assure your customer that TI has not changed the device. If the device works in the customer's application, it should continue to work.

    Regarding the change in the DAC8760 and DAC7760 datasheet, we have removed the daisy chain mode as a recommended mode of operation. As we had mentioned in the previous revision of the datasheet (in sections 8.3.10.1 and 8.3.11.1) there may be specific bit patterns that can erroneously cause the watchdog timer or the CRC to be enabled without a rising edge of the LATCH pin. These bit patterns were shown in Table 4 and Table 6 of the previous revision of the datasheet:

    With the use of the daisy chain, there may be a chance that this digital pattern could be seen through the course of sending multiple commands to multiple devices. This would accidentally enable the CRC or the watchdog timer.

    In the end, it's easier to use the device with a controller that can handle two independent sets of SPI, or use parallel SPI lines with separate /CS selections and a gated SCLK.

    If the customer is already using daisy chain mode and not having issues, then it is likely that their system does not ever generate these problematic bit patterns. Again, there is nothing that has changed with the device on this datasheet revision, so you should not expect any new behavior. We have removed daisy-chain operation from the datasheet to help avoid new customers having problems with the issue.


    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Guru* 97465 points

    Kazuya-san,

    Had entered in "Reply" a little too early. I've attached the original Table 4 and Table 6 from the previous revision (Rev C) of the datasheet to show the problematic bit patterns.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Guru 21505 points

    Hello Joseph,

    Thank you very much for your reply.

    Could I ask you an additional question as the following?

    I think the watchdog would be enabled when "Enable Watchdog Timer Digital Interface Pattern" is clocked into DAC8760 even if stand alone mode not daisy-chain mode is used.

    Is my thought not correct? 

    Thank you again and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 97465 points

    Kazuya-san,

    That is correct. If that bit pattern is sent to the device, it could inadvertently enable the Watchdog Timer. It does not require the device to be in daisy-chain mode to accidentally enable the Watchdog Timer.

    Joseph Wu