LM27762: low noise power supply for ultra low noise op-amps

xyz xyz

Part Number: LM27762
Other Parts Discussed in Thread: LMH6552, LMH6629, TPS65131, , LM5160

Hello

I'm designing some ultra-low noise amplifiers based on LMH6629 and LMH6552.

LMH6629 is at the front end of a sensor to amplify very small signals (uV to mV) and LMH6552 is for driving a high speed ADC.

LMH6629 needs ±2.5V/16mA and LMH6552 needs ±5v/16.5mA power supply .

actually I have a 5v 20W DC adapter.

my first choice is TPS65131 to boost up 5v to ±15volt. then I want to convert them to ±5 and ±2.5 with two ( TPS7A4700 and TPS7A3301 ).

But today I was encountered with LM27762 ! I think it's a nice choice bcoz it makes my design very compact and the noise is 22uVrms and is able to deliver (1.5~5V)/250mA to the consumers.

But I'm not sure about my choices! bcoz this is the first time I'm designing ultra-low noise circuits.

which one is better? which one is more reliable in ultra-low noise application?

I would be grateful if you could suggest a plan.

Regards

over 6 years ago

0 xyz xyz over 6 years ago

Intellectual 1000 points

I think I can find a proper anwser from the below link: (for ADC)
e2e.ti.com/.../noise-requirements-for-adc-power-supplies-

Thanks

0 Chris Glaser over 6 years ago

TI__Guru*** 144350 points

I think your first architecture, with the split rail followed by LDOs, will be lowest noise. LDOs need some voltage separation between Vin and Vout to reject noise. Usually, at least 0.5V is needed for best noise rejection. Going to +/-15V is excessive -- +/-6V should be plenty.

As well, the LM2762 will not give very good noise performance, since you have 5Vin and want +/-5Vout. It can be used for the +/-2.5V rails from your 5Vin.

0 xyz xyz over 6 years ago in reply to Chris Glaser

Intellectual 1000 points

thanks for your attention and recommendation.
producing negative voltage is always challenging for me!
but I could find some very useful documents:
look at page 16:
www.ti.com/.../tidud38.pdf

( www.ti.com/.../tida-01427 or www.ti.com/.../tidrs44 )
I think the above document is very practical and worthy. they have produced +5V from +15V.
if it's OK so I can use TPS65131 instead of LM5160. essentially they used Lm5160 Bcoz they also need +/-13V in their design :)
But it's a green light to my design But as you mentioned it's not a good choice.

(latest update: I simulated it with TI Webbench. I couldn't design +15 to +5V/0.3A using TPS7A4700 :| so you are right about it)

the below document is an industrial version of such application:
www.ti.com.cn/.../tidua78b.pdf

in an another post you mentioned a useful link:
e2e.ti.com/.../2174250
www.ti.com/.../tida-01405

Regards

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LM27762: low noise power supply for ultra low noise op-amps