ST3232 : abnormal waveform

[Zschau]

hello,

We are using ST3232 as new project design and I measured waveform as below, does this waveform is normal or not？

we use 3.3V power supply with 100nF ceramic capacitors.

do you have a solution

thank you in advance

[TFranke]

Hi,

the open question is: What exactly is the load of the signal shown on screen? Is it within limits or not? Just at the edge?

The RS232 standard specifies +/-3V as needed for communication which is fulfilled by the current design, but from my point of view the signal is too noisy and it will get worse with higher loading and with aging of the capacitors.

I would at least increase the V- and V+ capacitors from 0.1uF to 1uF to lower the ripple, or change all caps to 1uF to have higher output levels at higher loads.

BTW 1uF is recommended for all those caps by TIs MAX232 chip which is nearly the same...

Best regards,

Tobias