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WEBENCH® Tools/TPS7A8300: De coupling frequency range

Vilas Kumar
Prodigy 170 points
Part Number: TPS7A8300
Other Parts Discussed in Thread: CSD95480RWJ

Tool/software: WEBENCH® Design Tools

Hi Team,

In my design using LDO with part number "TPS7A8300RGWR" and its driving from the converter "TPS54622RHLR".  Here, using the de-coupling capacitors as recommended in the datasheet. 

Since it's in board design stage, i was performing board decoupling analysis using software simulation tools. I need to know up to what frequency level need to observe the PDN plot.  

  • 0
    TI__Mastermind 37065 points

    Hi Vilas,

    I have a lot of experience with the type of analysis you are describing.
    I may be misinterpreting your question.
    Decoupling analysis is used to obtain the AC impedance across frequency.
    It gives you an indication of whether your impedance is low enough for load transient responses.
    As such, running a Decoupling analysis is application specific. 

    Low speed circuitry have different requirements than high speed circuitry, such as high speed digital electronics with fast rising / falling edges, or high speed RF transmitters, etc.

    A typical linear regulator does not have a need for this type of analysis.
    You should find out what the rising and falling edges are for your digital circuitry, or what other transients you expect to see on the LDO output, to determine the frequency your PDN plot should go up to.

    I hope this helps.

    - Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 170 points

    Hi Stephen,

    Thanks for your valuable reply. 

    yes, i was trying to decoupling to obtain AC impedance across the frequency. 

    I agree that for linear regulators not need for decoupling analysis. But in our case we are considering the output power from the converter device. 

    Also i have one more doubt, you have mentioned that we may need to perform decoupling for high speed RF transmitters.

    Here in our present design we have one more circuit, the output power pins are taking from the part number "CSD95480RWJ" and it connected to our load FPGA device. We are using this power particularly for RF circuitry and running at 80A of current. In the design we have made connection as shown in the application diagram of the datasheet. But in the datasheet they have not given information regarding AC ripple and coupling capacitor. Is that necessary to perform decoupling analysis for that circuit even. 

    Thanks in advance for your response. 

    Regrds,

    Vilas Kumar S

  • 0 in reply to Vilas Kumar
    TI__Mastermind 37065 points

    Hi Vilas,

    For the FPGA, you will want to try and identify the load transients you expect to see from the FPGA during operation.
    In my experience, those transient requirements are hard to predict before a design is fabricated and measurements can be made across temperature.
    So the usual design flow is to maximize the quality of the layout with digital, RF and power needs in mind.
    If you are aware of approximate rise / fall times that the FPGA transients will be, you can use that knowledge and focus on those frequencies in the decoupling analysis. 

    What I am thinking of for RF applications is something like a transmitter, where the output power must be maintained and is not allowed to droop beyond a certain threshold.  If the rising / falling edges are very fast, then a decoupling analysis can help to ensure the impedance is sufficient under those conditions.  There are certainly RF applications out there where the rise / fall times are not as fast, and an engineering judgement can be made on whether to conduct a decoupling analysis in those situations.

    Regarding the TI datasheet you listed - I am not familiar with this component, and we would want to engage the switching converter group to better understand the ripple frequency if you are looking for that information.

    I hope this helps.

    Thanks,

    - Stephen