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TPS65273V: TPS65273V Passive component value Schematic check

Alex Wong
Prodigy 170 points
Part Number: TPS65273V
Other Parts Discussed in Thread: TPS51916

Hi Experts,

I have project using TPS65273V driving Xilinx UltraScale FPGA to provide voltage for DDR3 control

I have calculated the component value according to Datasheet and I want to ask do the Res/Cap/Ind value I using correct?

please let me know if any more info. needed.

Best Regards,

Alex.

TPS65273V_Sch.pdf

  • 0
    TI__Genius 12950 points

    Hi Alex,

    Thanks for reaching out. Would like to double check with you that do you use 3 TPS65273s? In order to better review the schematic, could you please let me know what is the input voltage, output voltage and output current of these 3 Dual Buck converters? I only see the first TPS65273V show these information.

    Thanks!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    Prodigy 170 points

    Hi Lucia,

    Thanks for reply. 

    My system have a 12V power supply.

    The first TPS65273V is feed for FPGA, so the output voltage / current is clear

    The second and third TPS65273V is for DDR3 Vref and Vtt termination

    I cannot find their current requirement in JEDEC Spec so far... so maybe I can refer to TPS51916

    Vref need 0.75V and 20mA

    Vtt need 0.75V and 2A

    p.s. my project will move on to DDR3L at some point, that's why I using programable Buck converters in my work.

    Best Regards,

    Alex.

  • 0 in reply to Alex Wong
    TI__Genius 12950 points

    Hi Alex,

    Please kindly see my comments shown below:

    1. Typically we don't need 56uH large inductor for this application. Even though the actual output current is small like 0.016A, you can use the maximum loading of TPS65273V to calculate inductance.  Actual output current 0.016A output current does not mean that the ripple current must be smaller than 0.016A*LIR(coefficient).

    2. What is your expected soft start time? Typically we can use nF level capacitor to get desired soft start time. 

    3. It is also recommended to add an additional 0.1-µF capacitor from the VIN pin to ground to provide high frequency filtering.

    Please kindly let us know if there is any more concern.

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    Prodigy 170 points

    Hi Lucia,

    1/ for the Inductor value, the equation (6) from datasheet make me question the why lower Iout require a higher Inductor.

    below are values I used in calculation

    Vin = 12V

    Vout = 1.8V

    LIR = let 2.5

    Iout = 0.016

    fsw = 513.8k

    and my calculation result is L = 74uH

    I am not very experience on choosing inductor, so I may misunderstand something.

    2/ sorry my calculation have not cover that cap value

    I think 5ms is enough, so I will use 47nF for all the SS pin.

    3/ thx for the advise.

    Best Regards,

    Alex

  • +1 in reply to Alex Wong
    TI__Genius 12950 points

    Hi Alex,

    Let me explain in more detail.

    In figure 6, Io can be the maximum output current which is 3.5A in this application. LIR is the coefficient that represents the account of inductor ripple current relative to the maximum output current. If you choose Vin=12V, Vout=1.8V, let LIR=0.25, Fsw=513.8k, you can get suitable L as (Vinmax-1.8)*1.8/(3.5*0.25)/(Vinmax*513.8k). Suppose Vinmax=12*1.2=14.4V(not sure of your actual Vinmax, just an example), the calculated inductance is around 3.5uH. The inductance you derived can already meet the current ripple requirement for output current range from 0- 3.5A. Thus, if your actual output current is 0.016A exactly, it is in the range of 0-3.5A which means that the inductance calculate before can meet your requirement. If you use 0.016A as Io in the formula, a large value inductance as 74uH will be derived which will be over spec and no need. It will also increase total solution size since the size of the inductor is big.

    Hope it will be helpful. Let me know if there is any more concern. Thanks!

    BRs

    Lucia