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I am still fairly new to DC/DC converters and was wondering how to generate negative output supply with a positive input supply. I don't know what the general requirements and limitations are but here's what I had in mind based on this application note:

enter image description here

Now, TI's Power Designer doesn't allow applying a negative output voltage for the TPS563300 and for obvious reasons I won't find the TPS563300 in the LTSpice library. Analog Devices, however, has the LTC3336 in their library and applying the topology shown above works at least according to simulations. The LTC3336, however, has a maximum input voltage of 16.5 V and going from +12 V down to -5 V spans 17 V, so I think this product is a no-go.

enter image description here

What are the criteria for allowing the generation of a negative supply from a positive input? I think one of them is the maximum input voltage with respect to the converter IC's ground. Is another one that the switching output (SW) has to be a half-bridge? From the simulation above it seems I need to take measures to avoid a positive supply during startup. What other things do I need to bear in mind or watch out for?

For completeness sake: I want to convert from +12 V to -5 V for a maximum current draw of 100 mA. Even though LDOs are cheaper alternatives where I don't have to go through the extra effort of EMI filtering, I want to avoid dissipating the excessive heat.

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I want to convert from +12 V to -5 V for a maximum current draw of 100 mA

It sounds like you are looking for an inverting converter: -

I found this reference design that produces -5 volts: -

enter image description here

There are likely to be other offerings from people like TI too.

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  • \$\begingroup\$ that's nice but there are cheaper solutions, such as the TPS63710 as I don't need such a large input range. Besides, it needs only one inductor and no diode. Thanks for your suggestion but it doesn't really address my original question. \$\endgroup\$
    – Hansel
    Commented Feb 20, 2023 at 14:25
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    \$\begingroup\$ @Hansel it does address your original question (which is about making a converter from 12V to -5V/100mA) by suggesting an "inverting converter". The schematic given is just an example and, as stated at the end of the answer, there are different options from other manufacturers such as TI. Yes, TPS63710 can be used but I strongly recommend you to run a webench design & simulation on TI website. \$\endgroup\$
    – Rohat Kılıç
    Commented Feb 20, 2023 at 15:53
  • \$\begingroup\$ Just to sure, here's my original question: "What are the criteria for allowing the generation of a negative supply from a positive input?" This is within context of my original post, referring to the link and the first diagram. \$\endgroup\$
    – Hansel
    Commented Feb 20, 2023 at 17:45

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