TPS54120: Power Supply Schematic Review for Reduced Noise

Hi 

Nancy will reply you tomorrow!

Shuai

Shyam, 

I am wondering if you have looked at the TPS62912 or TPS62913 for this application.  The noise and ripple performance of the device may meet your needs and has been used on several AFE and ADC designs shown on the product page at www.ti.com\tps62913. The efficiency would also be better, as well as the solution size. 

The reason why i have considered TPS54120 is the due to the reason of noise

DCDC followed by LDO and LC filters are one approach

can you help me to compare noise output of TPS54120 and TPS6291x

if i see the datsheet, it brought out that TPS6291 is at noise 20uV and 

TPS54120 is at much better postion at 4uV

correct me if i am wrong

but as you said efficiency of TPS54120 is very poor in comparsion 70% vs 90%, 

I assume this is a combined figure including LDO so the efficiency would have been low

Correct me in choosing better by elucidating above observations.

Hi Shyam,

Nancy will give you response once she come back to office!

BRs

Zixu

Shyam, Nancy, 

It is true that 4uVrms is lower than 20uVrms as a noise figure.  The real question is what do you need in your application.  It may be that you do not need 4uVrms, but can accept the noise of the TPS62913.  

4uV Rms noise holds good for me , one thing which confused me is the LDO ground of the three regulators , any ways PGND of all three regulatros i shall keep same.

but the  LDO_GND should be different and must be starred to a common ground at some place ?

kindly suggest on grounding of theree regulators.

Hi Shyam,

Yes, you should separate LDO GND and PGND. Please refer to TPS54120 EVM user's guide layout.

Thanks,

Nancy

My question is the LDO_GND or all three regulators should be different ? PGND of all three regulatros should be different ?

In layout i am using a common PGND for all three regulators which is actually connected to main ground via bead

i am maintaining seperate LDO_GND for all three regulators,namely LDO_GND1,LDO_GND2,LDO_GND3

using a net tie i am connecting LDO_GND to main PGND, some thing like below

as i have three regulatros its a different case on the EVM, basically idea is not to create shape and merge them( for sake of my layout engineers)

is my idea of net tie good for shorting LDO ground and power ground ?