The LMS36x5-Q1 control scheme allows this device to operate under a wide range of conditions with a low number of external components. Peak current mode control allows a wide range of input voltages and output capacitance values while maintaining a constant switching frequency. Stable operation is maintained while output capacitance is changed during operation as well. This allows use in systems that require high performance during load transients and which have load switches that remove loads as the operating state changes. Short minimum on and off times ensure constant frequency regulation over a wide range of conversion ratios.
This architecture uses frequency spreading to achieve low dropout voltage maintaining output regulation as the input voltage falls close to output voltage. The frequency spreading is smooth and continuous, and activated as the off time approaches its minimum. Under these conditions, the LMS36x5-Q1 operates like a constant off-time converter, allowing the maximum duty cycle to reach 98% and output voltage regulation with 650-mV dropout. As load current is reduced, the LMS36x5-Q1 transitions to light load mode. In this mode, diode emulation is used to reduce RMS inductor current and switching frequency. Average output voltage increases slightly while lightly loaded as well.
Fixed voltage versions do not need a voltage divider connected to FB saving additional power. As a result, only 18 µA (typical, while converting 13.5 V to 3.3 V) is consumed to regulate output voltage if output is unloaded.