When the voltage on the VIN pin exceeds the positive-going UVLO threshold, the device initializes as follows:
When initialization is complete, the device enables I2C communication and releases the EN pin. The external circuitry controlling the EN pin now determines the behavior of the device:
Figure 9-7 shows the start-up sequence when the EN pin is pulled up to VIN.
Figure 9-8 shows the start-up sequence when an external signal is connected to the EN pin.
The SSTIME[1:0] bits in the CONTROL2 register select the duration of the soft-start ramp:
The device ignores new values until the soft-start sequence is complete if the user programs the following when the device soft-start sequence has already started:
If the user change the value of VSET[7:0] during soft start, the device first ramps to the value that VSET[7:0] had when the soft-start sequence began. Then, when soft start is complete, the device ramps up or down to the new value.
The device can start up into a prebiased output. In this case, only a portion of the internal voltage ramp is seen externally (see Figure 9-9).
Note that the device always operates in DCM during the start-up ramp, regardless of other configuration settings or operating conditions.