User Guide
13 of 46
Rev. 1.0
2022-03-09
48V Battery Switch Reference Design
R 48V BATT Switch10
System and functional description
𝑅
𝑠ℎ𝑢𝑛𝑡
𝐿
𝑠ℎ𝑢𝑛𝑡
=
1
𝑅𝐶
Since resistors placed in series to the amplifier inputs will influence the gain factor they should be kept as small
as possible. With a chosen filter resistor value of R = 8.2
W
we get a capacitor value of
𝐶 =
𝐿
𝑠ℎ𝑢𝑛𝑡
𝑅
𝑠ℎ𝑢𝑛𝑡
𝑅
=
0.9 𝑛𝐻
50 µΩ 8.2 Ω
= 2.2 µ𝐹
Because the current distribution between the two shunts may be unequal, the two shunt voltages may differ
and therefore need to be balanced. This can be achieved by the compensation network shown in Figure 10. In
this circuit the voltage across the capacitor is the arithmetic mean value of the two shunt voltages while the RC
filter time constant remains the same.
Figure 10
Paralleled shunt resistors with parasitic impedance compensation
The chosen shunt resistors don’t have separate sense pins. Instead there is only a recommendation in the
datasheet on where to attach the sense lines to the footprint of the shunt. If you follow this recommendation
the voltage drop in the solder connection between the PCB pad and the shunt would be part of the sensor
signal. Since we are using very low ohmic shunt resistors, every µ
W
would add an additional measurement
error. Therefore, the footprint of the shunt was modified by introducing separate power and sense pads.
Figure 11
Improved connection of sense lines
