The device is in active mode when the following
occurs:
- The EN pin is above
VEN.
- VIN is above
VEN.
- VIN is high enough
to satisfy the VIN minimum operating input voltage.
- No other fault conditions are
present.
See
Section 7.3 for protection features. The simplest way to enable the operation is to connect
EN to VIN, allowing self-start-up when the applied input voltage exceeds the minimum
V
IN_OPERATE.
In active mode, depending on the load current,
input voltage, and output voltage, the LM644A2-Q1 is in one of six sub-modes:
- Continuous conduction mode (CCM) with fixed switching frequency and peak
current mode operation
- Discontinuous conduction mode (DCM) while in auto mode when the load current is
lower than half of the inductor current ripple. If current continues to reduce,
the device enters Pulse Frequency Modulation (PFM) which reduces the switch
frequency to maintain regulation while reducing switching losses to achieve
higher efficiency at light load.
- Minimum on-time operation while the on-time of the device needed for
full-frequency operation at the requested low-duty cycle is not supported by
TON_MIN
- Forced pulse width modulation (FPWM) similar to CCM with fixed-switching
frequency, but extends the fixed frequency range of operation from full to no
load
- Dropout mode when switching frequency is reduced to minimize dropout
- Recovery from dropout similar to other modes of operation except the output
voltage setpoint is gradually moved up until the programmed setpoint is
reached.