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 8-4 along with timing definitions.
The waveforms shown in Figure 8-4 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 8-1 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|