Electronic – USB + Power: Isolate or not

At my last company we found that USB-to-RS-232 converters can have a problem when they expect an almost instant responce from the RS-232 device. I was advised by the design engineer for our equipment that USB uses data packets. So when using USB, unless the software/drivers force a USB packet of data to be sent, the USB driver can hang around for more than a second (5000 ms) waiting for the packet to be filled before sending the incomplete data packet.

This meant that a lot of older DOS/Windows programs where they monitored RS-232 status lines would time out. The older programs often used timing loops based on looping a certain number of times... So as the PCs got faster, the polling got faster. As the length of time the polling continued to effectivly get shorter, USB came along.

The polling effectively became a memory location... (The drivers are usually optimised for maximum data packet throughput and didn't pass the status information on, because it was waiting to fill a packet). The drivers can sometimes be adjusted to help with this. FTDI drivers can adjust a lot of values in their configuration file. (Great for non-standard data rates.)

This meant we often had to run programs on desktops with RS-232 ports or drag the laptop base station out to the equipment to get it to work.

Additional information

See page 6 of the application note Advanced Driver Options for USB time out adjustments...

And for odd baud rates up to 3 Mbit/s, see Configuring FT232R, FT2232 and FT232B Baud Rates.

The datasheet for the TPS2115A you're considering lists its ESD ratings as 500V and 2kV (depending on the model) in the same 'Absolute Maximum Ratings' table which you're seeing the 6V limit.

I read that as 6V being the maximum sustained operating voltage (although proper operation above 5.5V is not implied).

While your teammate is correct in in his position that a 5V TVS device will not prevent the input voltage from rising above 6V during an ESD event, I believe that he is incorrect in saying that any ESD will automatically damage the device.
According to the datasheet, you don't need to ensure that an ESD event doesn't raise the input voltage above 6V - you rather need to ensure that it doesn't exceed the 500V or 2kV limits.
How you do that (filtering, TVS's, whatever) is another question.

Choosing a different device (with a higher voltage rating) does not give you any automatic assurance of ESD protection.