CCS/UCD3138: how to calculate the time of ramp up for HSFB ? have Calculation formula ?

Please refer to section 3.3 - Ramp module in the UCD3138's Technical reference manual:

http://www.ti.com/lit/ug/sniu028a/sniu028a.pdf

The parameters that involved are:

- DAC_VALUE in the EADCDAC register to set the starting level for ramp
- RAMP_DAC_VALUE in the RAMPDACEND register to set the end set pint level for ramp
- DAC_STEP (floating point value) to set the ramp slope

Leave the SWITCH_CYC_PER_STEP at it's default value of 0.
Please note,  since the ramp advances once per switching cycle, the slope is a function of switching period(Frequency).

Let us know if you have any further questions.