Channel 1 and Channel 2 enable and OCL trip setting pins.
Connect resistor from this pin to GND to set threshold for synchronous R DS(on) sense. Short to ground
to shutdown a switcher channel.
TPS51125 has cycle-by-cycle over current limiting control. The inductor current is monitored during the ‘ OFF ’
state and the controller keeps the ‘ OFF ’ state during the inductor current is larger than the over current trip level.
In order to provide both good accuracy and cost effective solution, TPS51125 supports temperature
compensated MOSFET R DS(on) sensing. ENTRIPx pin should be connected to GND through the trip voltage
setting resistor, R TRIP . ENTRIPx terminal sources I TRIP current, which is 10 µ A typically at room temperature, and
the trip level is set to the OCL trip voltage V TRIP as below. Note that the V TRIP is limited up to about 205 mV
The inductor current is monitored by the voltage between GND pin and LLx pin so that LLx pin should be
connected to the drain terminal of the bottom MOSFET properly. Itrip has 4500 ppm/ ° C temperature slope to
compensate the temperature dependency of the R DS(on) . GND is used as the positive current sensing node so
that GND should be connected to the proper current sensing device, i.e. the source terminal of the bottom
As the comparison is done during the ‘ OFF ’ state, V TRIP sets valley level of the inductor current. Thus, the load
current at over current threshold, I OCP , can be calculated as follows;
In an over current condition, the current to the load exceeds the current to the output capacitor thus the output
voltage tends to fall down. Eventually, it ends up with crossing the under voltage protection threshold and
shutdown both channels.