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MAX3232E: MAX3232E

Motaz Amer
Prodigy 10 points
Part Number: MAX3232E

I have a problem with my MAX3232E TTL-rs232 converter. the I have followed in my custom board the circuit in the datasheet wit the typical values.

the TTL signal comes from PIC32MX, the output should go to the computer. the voltage input level is 3.3V. the capacitors values are .1uF TANT, 35V.

the circuit worked very well at the beginning, it stayed working and I could transfer data between it and the computer successfully, then suddenly it stopped working!

I tried the next fixes:

  1. I started a typical fix by changing the IC itself with a new one:: still not working.
  2. changing the capacitors with new ones:: still not working.
  3. I checked the power levels, it is 3.3V and Ground, as it should.

I used an oscilloscope to check the problem, and here  is what I did and got:

  • I checked the TTL input, all good, from ~0V to ~3.3V.
  • I checked the RS232 output, here is the problem appears!! the output TX is all in Negative, at ~-6V.
  • the signal appears at TX line but still all in negative, and it seems like trying to get the full function signal bug still in Negative! the photo will show that.

  • the next photo shows the schematic

    this schematic is the base schematic of many of my designs and all of them works fine, even in this board I have 4 circuit of this! all of them works but this one!

  • this is the circuit layout

this  is all about the problem

any suggestions?

I can provide more info if needed.

and thank you very much.

  • 0
    TI__Guru 62920 points

    Hi Motaz,

    Thanks for providing all the details on this issue. Since it seems like the device isn't able to drive a high level, could you try holding a DIN port low to see if the DOUT voltage eventually reaches a positive level (it seems to be slowly increasing during each high period of your waveform capture)? Also, could you please monitor the V+ pin to verify whether the internal charge pump is working as expected and generating a positive voltage on this pin?

    Does the behavior change at all if the cable is unplugged?

    Also, have you tried replacing the transceiver with a new one? If this fixes the issue then it is likely there was some kind of damage to the chip.

    Regards,

    Max

  • 0 in reply to Miguel Robertson
    TI__Guru 62920 points

    Hi Motaz,

    I just wanted to check in to see if you had found a resolution for this issue.  If not, have you had a chance to look into my questions above?

    Regards,
    Max