lm2588-ADJ soft start calculation

Hi Jaden,

We've received your query and will get back to you with the equation shortly.

Thanks,

Anston

Hi Jaden,

Here is how soft start is performed on the LM2588 device (This is also true of LM2585 and LM2587). The softstart feature is possible through the compensation pin and an exact formula is not possible. However, it can be approximated when you consider the implementation. Immediately following power up the compensation capacitor(s) begins with 0V across it. During the soft start interval a current is sourced from the compensation pin slowly charging the compensation capacitor(s). During this period the voltage on the compensation pin increases causing the duty cycle of the switching to increase proportionally. This continues until the voltage sensed at the feedback input reaches the internal bandgap voltage of 1.26V. At that point the current source on the compensation pin is shutdown and the error amp loop is closed.

Hope this answers your query.

Thanks,

Anston

The product that uses the LM2588 is used in an aviation application which can have very badly behaving power sources that flicker.  So the problem is that I’m trying to predict how the LM2588 will behave (soft start) if the input power flickers.  What would the discharging mechanism be for the compensation capacitor be when the input power is briefly interrupted and then re-applied?  If the output caps discharge before the compensation cap discharges, the soft start might not behave after the flicker event and the inrush current that re-charges the output caps could be high. Plus, the soft start time could be much shorter.

Any insights on how it will operate in this application?

-Jaden