So I can easily make standalone temperature device but I want to produce 4-20ma also output corresponding to the temperature ... I wanted to interface PT100 which 100Ohm RTD. TMP112 is the on chip ...

That output (V OUT) can directly drive external meters, strip-chart recorders, and A/D converter inputs. Figure 2. This circuit provides fault protection and digital-signal recovery for a 4-20mA ...