Figure 8-22 describes the functional behavior of the internal device logic.

Figure 8-22 Functional State Diagram

DEVICE_OFF

During the DEVICE_OFF state the LM51770 is in shutdown. All internal logic and the DC/DC converter as well as the gate driver are off. The internal POR- system monitors the EN threshold to start the initialization of the reference system an device logic. The device current consumption is given by the shutdown current.

MAIN_LOGIC_ON

Once the LM51770 transits to the MAIN_LOGIC_ON state it will first stay in the POWER_STAGE_OFF state. Here the necessary checks and preparation for the start up are taken. The current consumption is given by the standby current.

HOLD-R2D

In this state the CFG-pin settings are read and the logic is storing this settings until the next EN -pin cycle.

READ_R2D

During the READ-R2D state the LM51770 executives the reading of the CFG-pin to get the selected settings determined by placed resistor.

POWER_STAGE_ACTIVE

The device executes the soft-start ramp during each entry to this state to avoid excessive inrush currents. In this state the power stage is active and the converter in operation. The current consumption is given by the active quiescent current of the electrical specification table.

TSD

The device enters the TSD-state if the silicon junction temperature exceeds the thermal shutdown limit. It automatically transits back to the POWER_STAGE_ACTIVE -state once the hysteresis of the thermal shutdown triggers.