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ADP2442 buck-boost simulation in LTSpice

Hello,

I am trying to simulate a buck-boost converter from 12V to -10V. I use the ADP2442 regulator model provided by the latest LTSpice version.

The output ramps down but then it flattens out at approximately -5.6V. I tried changing the feedback divider for other than -10V outputs but without results. As long as the output voltage set by feedback is above -5.6V (e.g. -4V) the supply works fine. This all happens with no load. For a load switch the supply enters in a current limiting mode precisely regulating the output voltage to Iout*Rout (about -4.4V=-550mA*8ohms) and continues switching without hiccups. The regulated current limit is far from the overcurrent condition.

Any possibility to have a bug in the ADP2442 model or am I missing something in the simulation? It should be noted that the exact same design has been built on PCB and is working without issues to output voltages down to -16V.

Please see the schematic attached for reference.

Thanks, Gabor

vpsm_fixed.asc.zip
  • HI Gabor,

    Thanks for pointing this out. The model has been revised. Please do "Tools--> SYNC Release" in LTspice to get the updated model. Note that the output still can not reach to -10V due to the current limit caused by too much Cout at the output in the simulation file your attached. Given 10V bias voltage, the functional output capacitance may be much less than that in the schematic.

    Thanks,

    Hong

  • Thanks for the answer and action, I'll update the LTSpice installation.

    Yes, the surge current caused by Cout at startup pushes the internal peak current and leads to hiccup. The real circuit we have built is actually a variable supply between -15V and -1V that requires very low ripple. We solved the startup issue by adding an additional soft start mechanism to the feedback loop that is activated whenever a large voltage/current jump is required.

    Regards,

    Gabor

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