Start-up and shutdown of the LM53625/35-Q1 are controlled by the EN input. Applying a voltage of ≥ 2 V activates the device, while a voltage of ≤ 0.8 V is required to shut it down. The EN input may also be connected directly to the input voltage supply. This input must not be left floating. The LM53625/35-Q1 utilizes a reference-based soft start that prevents output voltage overshoots and large inrush currents as the regulator is starting up. A typical start-up waveform is shown in Figure 12 along with timing definitions.
The waveforms shown in Figure 12 indicate the sequence and timing between the enable input and the output voltage and RESET. From the figure we can define several different start-up times depending on what is relevant to the application. Table 3 lists some definitions and typical values for the timings.
|tRESET-READY||Total start-up sequence time||Time from EN to RESET released||7.5||ms|
|tPOWER-UP||Start-up time||Time from EN to 90% of VOUT||4||ms|
|tSS||Soft-start time||Rise time of VOUT from 10% to 90%||3.2||ms|
|tEN||Delay time||Time from EN to start of VOUT rising||1||ms|
|tRESET-ACT||RESET time||Time from output voltage within 94% and RESET released||3||ms|