The TPS62135 is protected against overload and short circuit events. If the inductor current exceeds the current limit I(LIMH), the high side switch is turned off and the low side switch is turned on to ramp down the inductor current. The high side FET turns on again only if the current in the low side FET has decreased below the low side current limit threshold. Once the high side switch current limit is triggered for 512 subsequent switching cycles, the device stops switching. After a typical delay of 800 µs, the device begins a new Soft-Start cycle. This is called HICCUP short circuit protection. TPS62135 repeats this mode until the short circuit condition disappears.

Due to internal propagation delay, the actual current can exceed the static current limit during that time. The dynamic current limit is given as:

Equation 6.

where:

I_LIMH is the static current limit as specified in the electrical characteristics

L is the effective inductance at the peak current

V_L is the voltage across the inductor (V_IN - V_OUT) and

t_PD is the internal propagation delay of typically 50 ns.

The current limit can exceed static values, especially if the input voltage is high and very small inductances are used. The dynamic high side switch peak current can be calculated as follows:

Equation 7.