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MAX3243E: TX logic level changed and not works

Idan Atia
Intellectual 270 points
Part Number: MAX3243E
Other Parts Discussed in Thread: MAX3243

Hi,

I'm using MAX3243 to convert UART to RS232.

Usualy it works and i can measure on the TX of the MAX3243 -6[V], and when data is transmitted i can see the data (115200 bps) between -6 to +6 [V].

This was great!

But... suddenly sometimes I loose communication !

I measured the TX again (when the failure occured) and I see that the voltage level is 0[V], and when the data transmitted it changed between 0 to 4[V] (insted of +-6V). It's important to say that the waveform looks good (the same as before) but the voltage level different.

more info: I changed the MAX3243 to a new one and it was the same (sometimes work and sometimes not - the same effect of 0-4[V] data)

So my questions is:

1. Do you have an idea when and why (generally) the TX changed between 0 to 4 [V]? 

2. Do you have any idea how to understand what is the source of the failure?

  • 0
    TI__Guru 62920 points
    Hi Idan,

    Is there any kind of strong loading applied to the DOUT output that could be pulling the voltage down? (When I say "strong," I mean something with effective resistance below the RS-232 standard minimum receiver input resistance of 3 kOhm.)

    What is the status of the FORCEON/FORCEOFF and INVALID pins? I'm curious if maybe the device could be shut down unintentionally.

    Have you figured out what conditions induce the issue and what can be done to resolve it (e.g., power cycle, disconnect cable, etc.)? Or, does the issue persist permanently once it shows up on a given device?

    Could you please check the health of the V+ and V- rails by probing them on an oscilloscope? It would be good to look at these both under normal conditions as well as failing conditions. (Typically the DOUT output voltages will track V+ and V-, so I am curious if these are too low as well or if there is a voltage drop introduced by the output driver structure somehow.)

    Regards,
    Max