Tool/software: WEBENCH® Design Tools
LM5000
Dear team,
Could you please help me understand why webench refuses to select LM5000 when choosing these parameters:
The comment regarding why the part was not selected is the following : "This CC is running too long and being terminated by the system before it finished".. what does it mean ?
I think LM5000 should work perfectly with these requirements, but webench is making me doubt..
Many thanks in advance for your help!
All the best,
PA
Hello Howard,
Thank you very much for your support.
The issue is when Vin = 30V, Vout = 36V (and Iout = 300mA), I have the following message:
Thanks again!
Best regards,
PA
Hello Howard,
Thanks again.
I don't think this is the issue here, since the higher the input voltage goes, the lower the IC dissipation is (as it's a boot, Duty Cycle is lowering ans Vin goes up, and since the LM5000 is an async converter, the internal FET as less to dissipate: both less time and less current).
Please have a look at bellow extract from your test, where I modified the operating point to 30V, and where we can see the IC temperature raise is pretty limited:
Best regards,
PA
Hi PA,
I agree that at higher Vins, the IC should be cooler. But, there is a dynamically temperature loop in the CC looks at the full Vin range and it failed the temperature check.
As you can see below, the OpVal shows 124 deg C with Ta=25 Deg. C which just met the cutoff line of 125 Deg. C. Using default Ta=30 Deg. C, the design fails to create with a given conservative Theta JA value of 150 Deg.C/W.
So, I don't see this as an issue with WEBENCH but it's a conservative design tool which it has the flexibility to create the designs with forced input conditions.
.
