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  • TI Thinks Resolved

SN65C3232: SN65C3232

Part Number: SN65C3232

Built 10 prototypes, and 2 of 10 provide 'garbage' during RS-232 communication at 155200 bps. Charge pump capacitors are 220 nF 25V X5R at 3.3 V supply voltage. Can it be the problem? What are requirements and tolerance for those capacitors? What else may cause such failure? There are also 33 Ohms 250 mA thermistors in series with TX and RX pins 7 and 8 and TVS and 1 nF 50 V X7R capacitors and TVS 5V diodes from those pins to ground. Can 5V TVS cause such problems. It seems that it work fine with few characters, like OK, but does not provide correct characters with longer streams of data.

  • In reply to Oleh Kernytskyy64:

    Sorry to hear the problem. Can you list all the values of the external capacitors you used? I think 5V TVS diodes might be the problem here. TX output swing typical is from -5.4V to 5.4V. Can you also check if your diodes are bi-directional?
    Regards,
    Hao
  • In reply to Hao L:

    Capacitors values are 220 nF. TVS diodes are bi-directional.

    Measured Driver Output signal (DOUT2) on pin 7, and it has saw shape ripple (approximately 1 V peak to peak ripple).

    When changed capacitors to recommended for 3.3 V supply voltage value 100 nF -  signal on pin 7 became worst (deep voltage sags added after each second teeth ),

  • In reply to Oleh Kernytskyy64:

    It's OK to see some ripples on the output signal due to the internal charge pump circuitry. You can refer to this post (e2e.ti.com/.../463809) for the waveforms. The DOUT signal should be aligned the voltage level of V+ (pin2) and V- (pin6).

    Can you give more information how the device failed communication?

    Regards,

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