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MAX3232E-Q1: Output waveform noise

Vasu
Prodigy 160 points

Part Number: MAX3232E-Q1

Hello Team , 

Usig MAX3232EIPWR as the interface IC between the UART lines and RS232C components . 

Observed the sawtooth pattern waveform on the DOUT lines and RIN lines . 

Please suggest proper solution to resolve the issue . 

I cannot able to upload the waveform here . 

  • 0
    TI__Mastermind 23352 points

    Hi Vasu,

    Currently E2E has a glitch where you cannot upload files. This should be resolved soon. If the issue persists much longer, we can communicate over email. 

    However, your description of the problem is a common one. This is typically related to the VCC supply and the charge pump capacitors not regulating properly. 

    Please double check that you have selected the right capacitors your VCC supply voltage (3.3V or 5V). Refer to Figure 6-1 in the datasheet for the right values and placement.

    Have you measured the VCC input as well? Is it stable or is there a sawtooth pattern on VCC?

    If you have a protection diode present on the RS-232 bus, can you share the exact model number or link to the datasheet?

    Best,

    Ethan

  • 0 in reply to Ethan Sempsrott
    Prodigy 160 points

    Our VCC is 3.3 V and C1,C2, C3, C4 value is 0.1uF. Still, we are facing the sawtooth noise issue.

    Please suggest a suitable solution to resolve the issue. In VCC or DIN , ROUT line didn't have any sawtooth noise issue . 

  • 0 in reply to Vasu
    TI__Guru* 79531 points

    Vasu,

    This is considered normal behavior for this device. The sawtooth waveform is coming from the charge pump regulation. V+ will regulate to around 5.5V with some ripple which is what you see. V- will also do the same but at -5.5V.

    You could try to modify the charge pump capacitors to change the ripple. Changing the V+/V- caps to a larger value will result in less ripple but lower V+/V- values. I believe if you change the C1/C2 caps to a smaller value you may see more ripple. 

    I personally think the waveform isn't presenting a real problem and is acceptable for an RS232 signal.

    -Bobby