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LM2840: Inverting Buck-Boost Converter: -12vdc possible?

Part Number: LM2840
Other Parts Discussed in Thread: LM2841, , LM2736, TPS5430


I need a -12vdc output at about 50mA to drive some op-amps.  I have a choice of Vin to be either unregulated 16vdc, 3.3vdc (from an LM2736 output) or 12vdc (from an LDO). I prefer to use an LM2840 or LM2841 or another LM2736.

I read application note SLVA257A - Using the TPS5430 as an Inverting Buck-Boost Converter. I'm a bit confused about how to start though. I'm no expert at switching power supplies. The internal structure of the LM2840/41 shows a different driver than the TPS5430 and the LM2736 looks more complex.

I'd like to know if either LM2840/1 or LM2736 can be used as SLVA257A shows for the TPS5430 to generate -12vdc?


  • Hello,
    Yes, you can use the LM28401/1/2 for the inverting application. For 50mA output current and a low VIN of 3.3VDC, the switch current is calculated to almost 240mA. Therefore you might want to consider using LM2841 instead of LM2840. For a given topology, the component selection equations remain the same for different devices.