The LM61440 is in active
mode whenever the EN pin is above VEN, VIN is high enough to
satisfy VIN_OPERATE, and no other fault conditions are present. The
simplest way to enable the operation is to connect the EN pin to VIN,
which allows self start-up when the applied input voltage exceeds the minimum
VIN_OPERATE.
In
active mode, depending on the load current, input voltage, and output voltage, the
LM61440 is in one of five modes:
- Continuous conduction mode (CCM) with fixed switching frequency
when load current is above half of the inductor current ripple.
- Auto Mode - Light Load Operation: PFM when switching frequency
is decreased at very light load.
- FPWM Mode - Light Load Operation: Discontinuous conduction mode
(DCM) when the load current is lower than half of the inductor current
ripple.
- Minimum on-time: At high input voltage and low output voltages,
the switching frequency is reduced to maintain regulation.
- Dropout mode: When switching frequency is reduced to minimize
voltage dropout.