LT3758 Soft start functionality

Hi ,

I am quite not able to understand the soft start feature of LT3758 after going through the datasheet. The information given in the datasheet is very minimal. 

The startup waveform given in the Datasheet page no-33 for SEPIC converter shows that there is some initial delay before actual switching starts. This delay info is not explained in datasheet.

Also when i simulate the LTSpice model of this device for SEPIC converter, the results too show that there is an initial delay before 

- Softstart cap starts charging

- Comp node starts rising

and this delay is not constant but varies based on input-output voltage conditions.

Can you please help me understand

1. What this initial delay depends on ?

2. How actually comp node is controlled to achieve softstart feature ? 

3. Also, the equation given in the datasheet for Softstart time (tss) page-no:13 corresponds to which time ? Including initial delay time or excluding it ?

Thanks in advance.

Regards,

Maqbool

Top Replies