isolated vs non isolated DC-DC converters

[Peter]

I need to put a power supply on a board that converts 28VDC input to +/-
15VDC at about 100mA each. The +/-15VDC analog circuits will be receiving
and transmitting signals that are referenced to the 28V return. I'd like to
use a little prepackaged DC-DC converter module, but most of the choices
appear to be isolated types where the 28V return is isolated from the output
ground. Is it ok to tie the input and output grounds together even with an
isolated converter or should I only look at non isolated converters ?

Does anybody have any pointers to web sites or app notes which discuss this
? I've been looking and can't find any definitive information.

Can anybody recommend a non-isolated DC-DC converter module, reference
design, or vendor ? It can be linear or a switcher because I can filter the
output as necessary.

There seems to be some choices in the +5V to +/-15V converters, maybe I
should step down the 28V input to 5V first, but I don't have any circuits
that need 5V.

This is for a small, rugged application which will have to endure
temperature and vibration extremes.

 

[John Popelish]

I need to put a power supply on a board that converts 28VDC input to +/-
15VDC at about 100mA each. The +/-15VDC analog circuits will be receiving
and transmitting signals that are referenced to the 28V return. I'd like to
use a little prepackaged DC-DC converter module, but most of the choices
appear to be isolated types where the 28V return is isolated from the output
ground. Is it ok to tie the input and output grounds together even with an
isolated converter or should I only look at non isolated converters ?

(snip)
Isolated means you can hook it to anything you like, as long as you
don't exceed the isolation breakdown voltage.