In biblatex, make title sentence case but not journal name

The original definition of the bibmacro used to print the journal information is

\newbibmacro*{journal}{%
  \iffieldundef{journaltitle}
    {}
    {\printtext[journaltitle]{%
       \printfield[titlecase]{journaltitle}%
       \setunit{\subtitlepunct}%
       \printfield[titlecase]{journalsubtitle}}}}

Thus the instruction \DeclareFieldFormat[article]{titlecase}{\MakeSentenceCase*{#1}} impact the journal title as well. The solution is to modify the definition of the journal bib macro

\newbibmacro*{journal}{%
  \iffieldundef{journaltitle}
    {}
    {\printtext[journaltitle]{%
       \printfield[myplain]{journaltitle}%
       \setunit{\subtitlepunct}%
       \printfield[myplain]{journalsubtitle}}}}

where we can define a myplain field format that just produce an unformatted value.

\DeclareFieldFormat{myplain}{#1}

If you are trying to get the IEEE style you may want to use the following settings (details):

\usepackage[
bibstyle=ieee,% IEEE citation style
citestyle=numeric-comp,% citing multiple papers will produce format similar to [2,4-8,12] instead of [2,4,5,6,7,8,12] (optional) 
sorting=none,
backend=biber,
maxnames=100,% show up to 100 authors per author in the bibliography (optional)
isbn=false,url=false,doi=false% remove extra info (optional)
] {biblatex}

It will produce the intended results but it might modify other things too.