  The High Luminosity Large Hadron Collider (HL-LHC) will have a peak
luminosity of $5\times10^{34} $cm$^{-2} $\,s$^{-1}$, five times higher than the
design luminosity of the LHC. The hadronic ATLAS Tile Calorimeter TileCal) is a
sampling calorimeter with steel as absorber and plastic scintillators as active
medium. The light produced in the scintillating tiles is guided to
photomultiplier tubes (PMTs), where analogue signals are produced to be shaped
and conditioned before being digitized every 25\,ns. TileCal Phase-II Upgrade
for the HL-LHC will allow the system can cope with the increased radiation
levels and out of time pileup. The upgraded system will digitize and send all
the calorimeter sampled signals to the off-detector systems, where the events
will be reconstructed and shipped to the first level of trigger, all at 40\,MHz
rate. Consequently, development of more complex trigger algorithms will be
possible with the more precise calorimeter signals provided to the trigger
system. The new hardware comprises state of the art electronics with a
redundant design and radiation hard electronics to avoid single points of
failure, in addition to multi-Gbps optical links for the high volume of data
transmission and Field Programmable Gate Arrays (FPGAs) to drive the logic
functions of the off- and on-detector electronics. A hybrid demonstrator
prototype module containing the new calorimeter module electronics, but still
compatible with the present system was assembled and inserted in ATLAS during
June 2019, so that the Phase-II system can be tested in real ATLAS conditions.
