Hi everyone,
I’m just a newbie in SMPS design. I used MPS DC/DC Designer 3.19 to design a buck converter. I selected part MP38876. I have some questions:
1/ Pls help me to estimate the output transient ripple? I just found some equations below, but the result doesn’t match with the one calculated by MPS? And the V-under usually smaller than V-over calculated by my equations, but MPS result is V-under = V-over?
2/ Slew-rate is a factor that influence the V-out transient ripple, the more slew rate the more transient ripple (current step does not change), so how can i estimate the ripple when the slew-rate is changed?
Here is Ref-Design of MPS, I’m just changed the slew rate from 1 to 5 A/us.
I would suggest that the DC/DC designer will be more accurate. Those equations for instance don’t account for the ESR of the output cap. 5A flowing through 5mohm of ESR will cost you 25mV of drop extra and above what the perfect cap is charged to on the other side of the ESR.
Can you fiddle the ESR value in DC/DC designer?
Thanks for your attention.
I also think the tool is better. I just want to know how they can estimate the result.
I try to select a cap 330uF 3m(Ref-Design is 330uF 6m), the output transient ripple is higher. I know the actual result can be higher the calculated, but i need to estimate it in acceptable range.
Do you have any way(theory or exp) to estimate the maximum of V-under/over ?