LTM8058 Datasheet Input Current Versus LTSpice RMS Input Current


I'm working on a power supply design for a data acquisition system that requires high-voltage isolation and was interested in using the LTM8058 with a +15V input supply, stepping it down on the secondary side to a +5V and +3.3V supply. In trying to obtain input current draw numbers for the system, I created a LTSpice sim of the part using load resistors meant to emulated the expect current draw on the secondary side:

The loads should produce 50mA of draw on the 5V output and a little over 200mA of draw on the 3.3V output. The simulation shows that on the primary side of the supply, the RMS draw of the supply is about 230mA:

But the datasheet of the LTM8058 suggests I should be seeing much less, assuming I should lump the two currents together in reading this plot:

I have a few questions about the datasheet numbers then:

1.) Do the traces in the above plot apply to the draw from both the LDO and the flyback output or just the flyback?

2.) Am I correct in using the RMS current draw from the primary-side voltage source to estimate DC draw by the LTM8058 in my sim?

3.) How does the plot above calculate input current draw? Or is this reflective of actual data from bench testing?


Jeff Gilbert

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