Hello,
I've created the following Webench Design using the TPS40305 synchronous buck controller:
https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=D6E17A44DAF5EC1F
The sudden drop in efficiency (see attachment) between 11A and 14A output current caught my attention. I wanted to find out what is causing this drop.
Further investigation showed that at Iout 11.2A the power loss in the TPS40305 (IC Pd) is given as 569.04mW, while at Iout 11.3A the IC Pd spikes up to a whopping 6.06W. All the other power loss figures behave as you would expect (see attachments).
IC Pd then further increases slowly to reach a maximum of 6.13W at 11.9A. For higher currents Ic Pd drops continuously.
I have not seen any behaviour like this from any synchronous buck controller I have designed so far. There is also no word in the datasheet that the controller would switch any modes at such high output currents and no warning that the maximum IC power loss does not occur at maximum output current.
I can't explain what I am seeing. Therefore I currently assume that this is a Webench "bug". Please confirm.
Best regards,
Chris Dobler
