Need advise for negative rail

Prodigy 140 points

Other Parts Discussed in Thread: TPS7A39, LMC6061

I want to use TPS7A39 for producing +5V & -5V to power LMC6061 and some other instrumentation amplifiers.

My input main supply is 12V. How can I generate low noise negative rail as input to TPS7A39 to get -5V ?

Current requirement is not much, just few mA.

Should I use charge pump or some other DC-DC inverting regulator ?

Please suggest some low noise options for doing this.

over 2 years ago

0 John Schneider over 2 years ago

TI__Genius 12511 points

Hi BP,

Yes in order to get the negative voltage to supply the dual supply LDO you have linked, you would require a -5.25V or less rail to supply the device with. A voltage converter is desgned to accomplish this very task.

Additionally the LDO has strong PSRR, meaning input noise from the negative rail will be multiple orders of magnitude smaller after the LDO has processed the rail. It is always better to supply the cleanest input rail to the LDO as possible for best results, but if unable to achieve such a rail you may also put another negative LDO on the input to the device chaining them together to achieve a clean rail however this comes at the cost of another IC in the power rail.

Regards,

John

0 BP over 2 years ago in reply to John Schneider

Prodigy 140 points

Dear John

Thanks for your response.

My input main supply is 12V. How can I generate negative voltage from 12V to feed input to TPS7A39 to get -5V ?

for example how to generate -12V or -10V or -8V from 12V input ?

0 John Schneider over 2 years ago in reply to BP

TI__Genius 12511 points

Hi BP,

I am not an expert as I deal with linear regulators, but the buck team put together an app note detailing the procedure. If further questioning is required, they could help you understand the method.

https://www.ti.com/lit/an/slva458b/slva458b.pdf?ts=1686093674424&ref_url=https%253A%252F%252Fwww.google.com%252F

Regards,

John

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Need advise for negative rail