Hi,
I drew the following schematic:
It is an interface between RS232 and logic powered between 1.8V and 5V.
I would ask you for a review.
Especially the LEDs on the RS232 signals, I am afraid they cause too much degradation.
I tried two other variations.
One is this:
In this case, RS232 signals are connected to transistor bases. But the specification talks about a 3k load, so again I suspect it may not work. You also see two different configurations, one using VDD and VEE and one using only VDD. I don't know which one might be better.
in the last variant, I moved the leds to the ttl side, and thus the logic of turning on the leds must reverse:
again there are two variants, a simpler one but with worse consumption and a more complex one.
The question here, as in the previous case, is whether I can drain all this current from the VDD and VEE pins. There is no indication of this in the datasheet, so I suspect that I can't really use them at all.
If so, I would have to give up any LEDs on my board.
so in addition to reviewing the connections and components around the LTC2802, I ask if there is a reliable way to have activity LEDs on both rx and tx considering that the only reliable power supply I have can be as low as 1.8V.
