• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 22 subscribers
  • Views 309 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.

SN74AUP2G17: Buffer and Driver Selection

rimark
Prodigy 95 points

Part Number: SN74AUP2G17
Other Parts Discussed in Thread: TXU0204, SN74AUC17, SN74AUC2G125

Hi, 

I am currently exploring the use of buffers & drivers with the following specifications:

Cable Size: 28AWG -> 30AWG
Cable Length: Approximately 60cm 
Assumed Load Capacitance: 50pF

Digital Signals:
1 x UART (115200bps)
1 x PDM (3MHz)

Digital Logic: 1.8V

I am looking at the SN74 series from AUP, AUC or LVC. Preferably for a low power portable application. Likewise would it just be on the transmit side or would you recommend to buffer at the receive side of the cable as well?

  • 0
    TI__Guru* 97676 points

    Hello,

    What's going to be more important than size of wire is the controlled impedance of your transmission line. At 60cm, you will definitely see t-line effects, so having an impedance controlled line from start to finish will be important for signal integrity.

    If you're operating at 1.8V and using a 50 ohm t-line, then the AUC family will be your best option. It's designed to directly drive 50 ohm cables and is optimized for 1.8V operation, so there's no need for additional matching.

    I would recommend to buffer at the distant end also to minimize loading issues.

  • 0 in reply to Emrys Maier
    Prodigy 95 points

    Hi  ,

    Really appreciate your response which is very insightful!

    This does indicate that I would need at least 4 x AUC family for UART and PDM simultaneously placed at the transmit and receive side as well.
    Although, the host side does have an internal drive capability of up to 12mA but I had decided that buffering and line driving them externally would be the best to pass EMC / reject noise coupling into the cables from entering my system. 

    From a cost perspective, I had found that 2 x TXU0204 may be a suitable option as well from my application?
    Despite this being a level translator, the upside of this part is that it has 4 channels with 2 bidirectional paths for my application of UART + PDM. 
    I was thinking of just tying Vccb portion of this path from Vcca as well; as the opposite end of the cable is also powered by its own 1V8. 

    Deeply appreciate your expertise on this!

  • +1 in reply to rimark
    Guru 326430 points

    When both supplies are the same, then you can simply use a normal buffer like the SN74AUC17. (That the pins for the return path are on the 'wrong' side of the chip only makes the routing a little bit harder.)

  • 0 in reply to Clemens Ladisch
    Prodigy 95 points

    Hi  ,

    Deeply appreciate the response. Do you mean the SN74AUC2G125 as the 17 does not exist for 2 channel devices?

    Would that be having 4 x SN74AUC2G125  like below? Is it alright to mix the signals within the same device package?

    Host Side                                                                                                              Slave Side
    HOST_PDM_CLK -> SN74AUC2G125_A -> Cable -> SN74AUC2G125_B -> SLAVE_PDM_CLK_INPUT
    HOST_UART_TX -> SN74AUC2G125_A -> Cable -> SN74AUC2G125_B -> SLAVE_UART_RX

    HOST_PDM_DATA_INPUT <- SN74AUC2G125_C <- Cable <- SN74AUC2G125_D <- SLAVE_PDM_DATA_OUTPUT
    HOST_UART_RX <- SN74AUC2G125_C <- Cable <- SN74AUC2G125_D <- SLAVE_UART_TX


  • +1 in reply to rimark
    TI__Guru* 97676 points

    I expect he means the actual SN74AUC17, which contains 6 channels. If you need 4 total data lines at each end, then having a single IC with 4 channels + 2 unused channels seems like a good approach.

    You could also use the '2G125, but you'll need 2 of them at each end.

  • 0 in reply to Emrys Maier
    Prodigy 95 points

    Thanks for this   ! I wasnt aware that was an actual part based on my search filters!
    SN74AUC17 looks very suitable for my application but would also like to understand if there are smaller packages due to my size constraints of a wearable application.




  • 0 in reply to rimark
    TI__Guru* 97676 points

    The available packages are shown in the data sheet - if that device does not work due to size, you may consider other options, but I would expect that package to be the smallest total size due to the need for bypass capacitors for each package.