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TPS63710: Ultra Low noise negative supply design

Shyam Daram
Expert 1285 points
Part Number: TPS63710
Other Parts Discussed in Thread: TPS62912

Hi,

I have a power rail requirement of below

Polarity Voltage Load Current
 + 2.5 400 mA
 - 2.5 400 mA
 + 5 620 mA
 - 5 330 mA

Its already disucssed at Ultra Low Noise Power Chain for Photo Sensitive applications - Power management forum - Power management - TI E2E support forums

so i have finalised with recomendations and went forward with 62912 for both inverting and non inverting dcdc and LDO-TPS7A3301 and TPS7A9401

but due to the maximum voltage limitations of 62912 in inverting mode, Engineers have awared me of risk in operating at neck level

hence i wish to use the TPS63710, which is supposed to be ultra low noise DCDC as indicated by  at Ultra Low Noise Power Chain for Photo Sensitive applications - Power management forum - Power management - TI E2E support forums 

I request to help more on designing using TPS63710, can i directly replace TPS63710 in placed of TPS62912 ? (not pin to pin but design level)

I am going currently with a DCDC >  Line Filter > LDO for better SNR performance( schematic )

so in same line can i use TPS63710 Followed by CLC Filter followed by LDO for better SNR performance ?

Kindly respond with necessary suggestions

  • 0
    TI__Expert 7320 points

    Hi Shyam,

    TPS63710 is an inverting buck converter which could only support negative output voltage.

    For -5V and -2.5V application, it's suitable to use TPS63710.

    For better SNR, you need to add an LDO after TPS63710 but there's no need to add a second LC filter.

    That means you can use TPS63710 > negative LDO solution this time.

    Regarding the schematic, TPS63710 can directly support negative output and no need for Buck-Boost Topology but just follow the schematic in the datasheet.

    Please let me know if you have further questions.

  • 0 in reply to Athos Zhao
    Expert 1285 points

    should i need to use CLC filter alter LDO ? or you meant to say filter is already present inside DCDC ? i wish to use the CLC filter like i used for 62912 for better performace, kindly advice, my previous experience with dcdc with out clc filter is very bad, so i am bit sceptical of not accomodating a clc filter.

  • 0 in reply to Shyam Daram
    TI__Expert 7320 points

    Hi Shyam,

    TPS62912/3 could support 2nd stage LC filter internally but TPS63710 don't have this feature. You can find the suggested schematic in the datasheet.

    If you must use the 2nd LC filter, you need to have a full test of the loop.

    In my opinion, if you already use an LDO after DC/DC, it's ok not to use a 2nd LC filter.

  • 0 in reply to Athos Zhao
    Expert 1285 points

    can you please suggest a DCDC with support of output LC filter and low noise ?

    if not you meant to say, even if you choose one its performance with output LC filter is less than 63710 ?

    is the LDO im currently using compatible or any alternatives are to be chosen for better performance ?

  • +1 in reply to Shyam Daram
    TI__Expert 7320 points

    Hi Shyam,

    I'm confused why you must have a 2nd stage LC filter.

    You request is low noise and low ripple.

    TPS63710 has low noise feature and you can realize low ripple by adding a LDO.

    Thus I think TPS63710 and LDO solution is suitable for your request.

    We only have TPS62912/3 which can support 2nd stage LC filter, but as you said it has risk of input voltage over spec while using as an IBB.

    The LDO you choose is good for this application.

  • 0 in reply to Athos Zhao
    Expert 1285 points

    Hi attached  is my final schematic, i used web bench and EVK and modifed few things, can you please drop your valuable comments

    NV_DCDC_5V35_2V85.pdf

    1. Dont want to use PG,so left open

    2.directly connected VAUX Cap other end and 10th pin to GND directly

    3.Used similar caps to WB Design

    4.Used Inductor 74438357047

  • 0 in reply to Shyam Daram
    TI__Expert 7320 points

    Hi Shyam,

    The schematic of TPS63710 looks good.