Post Go back to editing

Current/Power limitation of the LTM8056

Category: Hardware
Product Number: LTM8056

Hello,

I have been looking into using the LTM8056 to generate 24V from a 8.5V - 34V input voltage range. I noticed in simulation that for high loads and smaller input voltages, the output power would be limited to a set value which seem independent of the adjustable output current/voltage limit. It also seems suspiciously close to the edge of the datasheet operational curves.

Although this operation is likely out of spec, could you tell me more about the mechanism which limits the power in that condition? I suspect a switch peak-current limit but I cannot find anything about that in the datasheet.

See here-under simulation results which clearly show how output voltage is held below 24V for a high load (16R).

  • You already named your problem: Asking for too much power. These diagrams show output power derating vs input voltage and possible output power nicely:

    With 7V Vin the LTM8056 will not deliver more than 1A@24V And with 8.5V input you will not achieve 36W of output power. 

    The switch peak current limit will not allow for more power/output current than shown in the datasheet diagrams and shown by your simulation result. Allow for some margin depending on your final efficiency.

  • Hey Markus,

    Thank you for the answer which at least confirms what I observed.

    From your reply I understand that the limitation is defined by a hardware internal switch peak current limit. Can I find an exact number for that limit anywhere which would allow me to calculate exact maximum output current for set in/ou voltage? The plots aren't very quantitative.

    Is there any risk operating the device on that limit for extended times or has it been designed such that this is part of nominal operation?

    Thanks again for the help.