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MAX3232-EP: NOISE WAVEFORM ISSUE AT 7PIN DOUT2 OF DEVICE

Daniel Lee68
Prodigy 90 points

Part Number: MAX3232-EP
Other Parts Discussed in Thread: MAX3232,

HI,

I'm developing our equipment to use MAX3232MPWEREP Device.

During interface PC to our board used the device through RS-232, as below picture noise is occurred at 7pin(DOUT2) of the device.

the noise is make error value in pc program.

the noise don't disappear any debugging. please let me know how to solve the issue....

thanks.

  • 0
    Prodigy 90 points

    noise waveform picture don't display above question so attache the file.

    please refer to attached file.

  • 0 in reply to Daniel Lee68
    TI__Mastermind 25705 points

    Hi,

    Could you share your schematic? What's the frequency of the noise? Does the waveform refer to MAX3232's ground? How's the input look like? Is the board ground and PC ground related? Without input data, can you capture the waveform of the V+/V- pins (pin2 and pin6)? What's the supply and does it have any noise or current limit?

    Regards,

    Hao

  • 0 in reply to Hao L
    Prodigy 90 points

    Hi,

    please refer to below for your questions.

    RS-232 signal connection => 

    schematic

    The noise frequency is 7.142Mhz.

    MAX3232's input waveform is as below at 10PIN(DIN2).

    MAX3232's input waveform is as below at 7PIN(DOUT2).

    waveform of the V+/V- pins (pin2 and pin6) is as below.

    power voltage is 3.3V and no noise and current limit.

    thanks.

  • 0 in reply to Daniel Lee68
    TI__Mastermind 25705 points

    Thanks for the waveforms. Can you check if V+ is toggling? V+ is the positive output of internal charge pump, which should stay at around 5.4V. Also the output of MAX3232-EP should swing from -5.4V to 5.4V. Please refer to this blog. If you test the device itself, does it work normally? What do the signals look like? BTW, what's the voltage rating of the capacitor?

    Regards,

    Hao

  • 0 in reply to Hao L
    Prodigy 90 points

    HI,

    Thanks for your advice and sorry waveform of pin2(V+) is wrongly posted. so again post as below.

    V+ is +5.4V with ripple.

    the voltage rating of the capacitor is 50V and 0.1uF.

    The pc program reads the register value of the encoder normally and sometimes reads abnormal values.

  • 0 in reply to Daniel Lee68
    TI__Mastermind 25705 points

    Thanks for your update. The transceiver charge pump looks working normal to me. Can you check the functionality of device itself with dedicated supply and signal generator? If it looks OK, can you repeat the testing with connecting dongle's ground with board's ground?

    Regards,

    Hao

     

  • 0 in reply to Hao L
    Prodigy 90 points

    HI, 

    thanks for your support.

    When enter 3.3V power input the MAX3232 device. the noise is occurred as below.

    I don't understand why the noise is occurred. 

  • 0 in reply to Daniel Lee68
    TI__Mastermind 25705 points

    Hi,

    Is the waveform from the Dout2 pin? How about Dout1? Another question is if you see the same behavior if the device is standalone with its own supply and ground.

    Regards,

    Hao