LM5164-Q1: Negative rail configuration

Karl,

Yes you can use the LM5164-Q1 in an inverting buck-boost topology. You've designed these before so you're probably familiar with this app note, "Using a buck converter in an inverting buck-boost topology." This app note explains the considerations of the chosen buck and details the operation of the topology.

-Sam

Sam,

Despite reading, Using buck convers in inverting mode. It still has not been possible to get a satisfactory outcome. Configured as shown below but still fails to operate. Therefore, I am questioning whether I have incorrectly configured it.

Regards

Karl

Karl,

Do you have a simulation AND a PCB? Which does not work?

Simulations often do not work for inverting-buck-boost because the GND pin can be internally connected to system GND. If the sim is not working, this may be the issue.

If the board is not working, does the sim work?

Thanks,

-Sam

(Hi Sam,

I have a TI evaluation board (LM5164-Q1EVM-041 Converter Evaluation Module) that was initially tested as +12V output. I then hacked the evaluation board to isolate components and connections from ground in order to enable the grounding of the positive output. Which should have caused the isolated circuit that was previously grounded to go negative (-12V).

However there appers to be no output when configured in such a way.

Regards

Karl

Karl,

You should be able to take the unmodified EVM and connect Supply+ to VIN and Supply- to VOUT to get an inverting buck boost where the GND pin of the IC is now considered -VOUT and the VOUT of the buck converter is now GND. You may need to add a capacitor from VIN to VOUT (of the buck, GND of the inverting buck boost) but you should not need more modifications than that.

If you have an unmodified EVM, you can try that. Or you can put the EVM back in its original state and try.

-Sam

Hi Sam,

All good now, many thanks

Regards

Karl