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TRS3232: Saw noise coupling with output

CHEN YAN
Intellectual 1430 points
Part Number: TRS3232

Hi,

Customer met an issue when use TRS3232, they found there is a saw noise coupling with output voltage. Please see pictures below. Could you please help me analysis the reason behind, thanks.

with load,

without load,

  • 0
    TI__Guru 62910 points

    Hi Chen,

    This device (and most other RS-232 transceivers) uses a charge pump circuit to generate the higher-voltage bipolar V+ and V- rails from a single logic supply (VCC).  The output (DOUT) is then switched to either the V+ or V- rail in order to represent "0" or "1" bits.  Some sawtooth ripple is inherent in a charge pump design since it is a switching regulator.  You can read more about how the charge pump works and what factors influence the ripple in this technical article:

    https://e2e.ti.com/blogs_/b/analogwire/archive/2018/06/28/how-the-rs-232-transceiver-s-regulated-charge-pump-circuitry-works

    The amount of ripple in these waveforms captures doesn't look unreasonably high to me, but if you wanted to reduce it further you could look into using different capacitor values as described in the above link.

    Please let us know if you have further questions.

    Regards,
    Max