I created a design with three LM5007s, switching at 1MHz. I used the Webench tool to do this, and there was no warning that the frequency I was selected was outside the recommended range. The output of the simulation was satisfactory, so I used it. I had the PCBs assembled, and they work well with no issues.
Fast forward to two days ago. I was re-reading the datasheet for another reason when I notice that there is a minimum recommended turn-on time associated with Ron. Then I noticed that frequency was also set using Ron. I calculated my turn-on time, and it was below the minimum time. I then realized that my switching frequency must be outside the recommended range, but there is NOTHING in the datasheet that mentioned switching frequency range. The word "Hz" isn't even in there. I looked further and found the LM5007 calculation spreadsheet, and it says the max recommended switching frequency is 580 kHz.
So here are my questions/thoughts on switching frequency:
- You might consider making the max recommended frequency a little more clear in the datasheet.
- What are the consequences of running an LM5007 at 1MHz? Will it cause any harm? Any instability? I have not seen any issues yet, but I have not checked inrush behavior or all possible loads that the circuit will see. Regardless, I am going to back off to 500kHz on the next revision.
Second topic: Overcurrent limiting. Based on the datasheet, it appears the longest off time that can be achieved at overcurrent is 17uS? Is that correct? Is there any way to make that off time longer, like a few mS?
Thanks!
