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TRS3221E: SCH review of TRS3221EIDBR

Lisa Xu
Intellectual 495 points
Part Number: TRS3221E
Other Parts Discussed in Thread: TRS3221

Dear TI Team:

 we have TRS3221EIDBR in our design, and the SCH is attached

1. Pls help review the sch attached, Thanks

2. Does TRS3221E need pullup on TIN and ROUT pin ?

   This is not mentioned in TRS3221E datasheet. but I checked Figure 3-1 of TRS3221 EVM User's  Guide, the TIN and ROUT are pullup by 10k (R1 and R2) to VCC (3.3V).

Best Regards

Lisa

  • 0
    Guru 275570 points

    The transceiver has a controlled slew rate; R17/R18 are not necessary ( but do not hurt).

    DIN needs a pull-up if the UART_TX signal might be inactive at any time. ROUT would need a pull-up only if the receiver could be disabled with /EN, i.e., not in this application (but it would not hurt).

  • 0 in reply to Clemens Ladisch
    Intellectual 495 points

    Hi Clemens:

    Thanks for your suggestion, We plan to reserve pull up resistor for DIN and Rout, If that ,the resistor should be close to Host or TRS3221EIDBR?

    Best Regards

    Lisa

  • 0 in reply to Lisa Xu
    Guru 275570 points

    This does not matter.

  • +1
    TI__Guru 57730 points

    Hi Lisa,

    Here is my check of the schematic

    Checked Status (Good, Bad, Okay, ?) Additional Comments
    Schematic pinout matches datasheet pinout Good
    Schematic net names match expected schematic pinout Good
    Local decoupling caps  Good
    No floating Input pins ? DIN is an input pin, in schematic its not clear if there is a situation where it could be floating. You may want to place a weak pull up resistor (~10k) on this pin if it could float.
    Cap values on charge pumps match datasheet recommendation Good

    As Clemen's mentioned Rout can use a pull up resistor if it's in tristate mode while the connected device is set as an input pin. 

    Lisa Xu said:
    Thanks for your suggestion, We plan to reserve pull up resistor for DIN and Rout, If that ,the resistor should be close to Host or TRS3221EIDBR?

    As Clemen's stated, this doesn't matter for this type of datarate/speed. You can use a weak resistor like ~10k and place it anywhere it is convenient .

    -Bobby