User Guide
41 of 46
Rev. 1.0
2022-03-09
48V Battery Switch Reference Design
R 48V BATT Switch10
System performance
4.2
Precharging
As described in chapter 2.3 “Basic operation”, the precharge path will be activated for a configurable time
before switching on the main path, when the switch is turned on by pressing button 1 or with the “on”
command in the command line interface. This is done to avoid inadverted tripping of the overcurrent detection
due to excessive inrush currents caused by capacitive loads at the output.
Figure 48 shows the load voltage (VLD) and the load current (ILD) over time when switching on with a 10
millifarad capacitor as load with a precharge time of 500 ms. First the precharge path (channel B) is switched on
and the current is limited by the 10
W
precharge resistor. As the capacitor charges up, the current decreases
exponentially. After the precharge time has expired, the main path (channel A) is activated and the remaining
capacity gets charged with only the switch and cable resistance as current limitation which results in a short
current spike.
Figure 48
Switching on with 500 ms precharging pulse (10 mF load)
If the precharge time is shortened, the remaining capacity to be charged is bigger and therefore the current
spike at activation of channel A is higher, as can be seen in Figure 49.
Figure 49
Switching on with 300 ms precharging pulse (10 mF load)
