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LM5041: design tools and questions

Sunny Qin
Expert 4890 points
Part Number: LM5041

Hi Team,

we found datasheet of LM5041 is quite simple, we can not found detail design guidance and calculation(like comp SS CS calculation), do you have any design tools or guidance documents to share?

And another question is: when customer power off LM5041 circuit(UVLO trigged), they found the buck will power off firstly, then push-pull power off, is there any way to make push-pull power off firstly then buck power off？As customer found if buck power off before push pull, output capacitor`s voltage will still keep high voltage and that`s not customer want.

Thanks.

Regards, Sunny

  • +1
    TI__Mastermind 26035 points

    Hi Sunny,

    There is an application note that I found by a web search based on the eval board but TI does not have a design tool for LM5041. The SS and CS calculations are straight forward and easy enough to follow in the data sheet. For the compensation, how about downloading and trying TI Power Stage Designer, which has an integrated control loop calculator you can experiment with?

    Regarding your question about cascaded shutdown, I'm not sure I understand? During UVLO off state, the buck outputs will default to HD LOW and LD HIGH. HD LOW means VIN is disconnected from supplying voltage to the push-pull (p-p) input. LD HIGH means the buck inductor is pulled to GND to help discharge the buck output capacitor while at the same time the p-p remains switching to assure the buck output capacitor is fully discharged. Since the buck output capacitor is a "link" between VIN and VOUT, we want this capacitor fully discharged before the next soft start cycle. This leaves the VIN capacitor fully charged to VIN (as long as VIN is still present) and the VOUT capacitor discharging according to the load present at VOUT. I believe this is the correct turn off sequence for a cascaded, current fed p-p. I don't know of a way to reverse the turn-off sequence but if the VOUT capacitor is not discharging fast enough, is it possible to decrease the feedback resistor divider so that VOUT sees more "non-switching" load?

    Thanks for connecting through E2E.

    Regards,

    Steve M

  • 0 in reply to Steven Mappus1
    TI__Expert 4890 points

    Hi Steve,

    Many thanks for your comments, it`s very clear.

    Regards, Sunny