User Guide
14 of 46
Rev. 1.0
2022-03-09
48V Battery Switch Reference Design
R 48V BATT Switch10
System and functional description
2.2.6
Hall based current sensor
In addition to the shunt based current measurement there is a hall based current sensor implemented to
provide an alternative current monitoring path for improved functional safety. It is located on the high side,
directly after the BAT+ input terminal. Thanks to the intrinsic galvanic isolation of the
TLE4972-AE35D5
there is
no need for additional isolators or level shifters. It can be directly connected to the microcontroller. The sensor
offers two analog outputs for differential current measurement and two digital outputs for fast overcurrent
detection with programmable thresholds.
Figure 12
Hall based current sensor TLE4972-AE35D5 with peripheral components
The sensor itself actually measures the magnetic field caused by a current conductor. Only in conjunction with
that conductor (or current rail) it becomes a current sensor. In our case the conductor is a short piece of PCB
trace in the middle layer right below the sensor where all the load current is forced through. The trace is only
3 mm wide but also only 1 mm short and 800 µm thick, with a resistance of only 7 µ
W
. The resulting power
dissipation therefore is 7 times smaller than that of the shunt resistors.
Two hall probes in the sensor measure the magnetic field around the conductor differentially. This ensures high
robustness against stray magnetic fields.
To avoid disturbances due to eddy currents in adjacent conductors the area beneath the current rail is kept free
from metal. That means that there is a cutout in the bottom layer around the current rail as well as a milled-out
area in the heatsink below that structure (see Figure 29 and Figure 34).
Figure 13
Hall sensor placement above current rail in middle layer
