Figure 8-11 OCP Duty Cycle Limiting Waveforms

In addition to valley current limiting, the LM5145 uses a proprietary duty-cycle limiter circuit to reduce the PWM on-time during an overcurrent condition. As shown in Figure 8-10, an auxiliary PWM comparator along with a modulated CLAMP voltage limits how quickly the on-time increases in response to a large step in the COMP voltage that typically occurs with a voltage-mode control loop architecture.

As depicted in Figure 8-11, the CLAMP voltage, V_CLAMP, is normally regulated above the COMP voltage to provide adequate headroom during a response to a load-on transient. If the COMP voltage rises quickly during an overloaded or shorted output condition, the on-time pulse terminates thereby limiting the on-time and peak inductor current. Moreover, the CLAMP voltage is reduced if additional valley current limit events occur, further reducing the average output current. If the overcurrent condition exists for 128 continuous clock cycles, a hiccup event is triggered and SS is pulled low for 8192 clock cycles before a soft-start sequence is initiated.