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TRS3232: Circuit review

Roy Chou1
Genius 16100 points
Part Number: TRS3232

Tool/software:

Team,

May you review the circuit for me? Thank you.

Roy

  • 0
    Guru 316690 points

    The DIN2 input must not be left floating.

    You do not need 50 V capacitors.

    The TRD1+/TRD1− lines are intended to transmit a differential signal. The RX and TX signals are independent, and their signal edges are likely to be coupled as noise into each other. You should transmit RX and TX in separate twisted pairs.

  • 0
    TI__Guru 72771 points

    Hi Roy,

    TRS3232E
    Checked Status Additional comments
    Schematic pinout matches datasheet pinout Good
    Local decoupling on Vcc Good Good
    Charge pump capacitors are sized properly Good
    Inputs are biased (not floating) Bad The TTL input DIN2 should not be floating. Please tie this to Vcc with a weak pull up resistor like 20k. 

    I also usually recommend customers put pull up resistors on the DIN pins that are connected to the MCU and the Rout pins. This ensures the DIN doesn't float when the MCU isn't actively driving the pin (if it's hi-z/tri stated). If the RS232 device is disabled or unpowered, we want Rout to be high if the MCU is on to ensure a glitch doesn't occur on the pin that might look like a start bit. 

    -Bobby