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TPS65270EVM: TPS65270

ilya feldman
Prodigy 130 points
Part Number: TPS65270EVM
Other Parts Discussed in Thread: TPS65270,

Hello

I would like implement in my protest a TPS65270

1. for reference design i use the BOM according to TPS65270EVM.

All components have size 0603 or high, is it mandatory? can you suggest to me what components i can reduce to 0402 size and what parameter is mandatory in capacitor and resistors ?

for example:

2. Exist a Inductor in outputs, what a mandatory parameter important in Inductor selection?

(for example: DC resistance, current saturation, Inductor tolerance, etc )?

  • 0
    TI__Mastermind 19080 points
    Hi,

    1. Of course you can use other footprints like 0402.
    Just pay attention to the different DC bias derating coefficient for different capacitor footprints. This derating affects the effective capacitance. Cin, Cout need to be checked.

    2. The most important parameters are effective inductance and rated current.

    Regards,
    Sam
  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 130 points

    Hi,

    1. sorry, what is "DC bias derating coefficient", can you please write a example?

    2. "Rated current", - if i would lead up to 2A through the coils, the Rated current should be multiplied - 4A ?

    Regardsת

    Ilya

  • 0 in reply to ilya feldman
    TI__Mastermind 19080 points
    Hi Ilya,

    Sorry for confusing you...
    1. For the DC bias degrading coefficient, I mean, the effective capacitance will decrease when a DC voltage is applied across the ceramic capacitor. The degrading is related to footprint. If you want to change the footprint, please pay attention to the effective capacitance of your new capacitor. Usually you can get the information on capacitor manufacturer's website.
    2. For the rated current, you need to consider the peak inductor current, not the output current. It's not simply doubling the output current. You can refer to the datasheet, chapter 9.2.2.1 to calculate it.

    Regards,
    Sam
  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 130 points

    Hello

    1. Please help me understand, how you calculate that indicator value in reference design - 4.7uF?  and not other value? please give me the equation.

    2. the result of indicator from the equation below is uH?

  • 0 in reply to ilya feldman
    TI__Mastermind 19080 points
    Hi ,

    The equation is Eq(4) in datasheet chapter 9.2.2.1.
    For the design procedure, you can refer to chapter 9.2.2.

    Regards,
    Sam
  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 130 points
    Hi Sam

    Sorry for misunderstood, in order to get 4.7uF, what value you have insert to Eq(4) in datasheet chapter 9.2.2.1.
    1.
    Fsw? is in MHz or KHz - what a frequency you select?
    LIR?

    2.
    I have RFID that work in 13.56MHz and BLE in 2.4GHz
    Please help me choose /suggest the correct Fsw for my application.

    3. If i decide work at Fsw = 800KHz, my max current 2A, Vout - one is 5V and the second 3.3V
    The L should be 12uH?

    Thank you
    Ilya
  • 0 in reply to ilya feldman
    TI__Mastermind 19080 points

    Hi Ilya,

    1. In the equation, Fsw is in Hz, inductance is in H.

    2. A few hundred kHz is good I think. As the switching frequency is well below your RF frequency range, so it should have limited effect on your wireless application as long as you have a good layout(refer to the layout guideline in datasheet).

    3.With below condition, Vin max is 12V, LIR=0.3, 

    for 5V output you can use 6.8uH(calculated result ~6.1uH), for 3.3V output you can use 4.7uH(calculated result ~5uH).

    Regards,

    Sam

  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 130 points

    Hello

    Thank you for support .

    1.Can you please explain to me, for which application or condition you choose LIR = 0.1 and for which LIR  = 0.3 ?

    2. In TPS65270 document for evaluation Module (see below), write that Fsw = 620kHz, for that value the resistor Rosc should be 414Kohm while existing resistor 383Kohm.

    is Rosc value not should be very accurate? it's not supposed to be from Rosc you choose the L value?

    .

  • 0 in reply to ilya feldman
    TI__Mastermind 19080 points
    Hi Ilya,

    1. Typically, we choose a value between 0.2~0.4 for LIR.
    The control loop need some current ripple on the inductor to maintain the Vout regulation. Usually we choose a value higher than 0.2. The larger inductor current ripple you have, the more output capacitance you need to get a smaller voltage ripple on Vout, that's why we choose a value below 0.4. The range is just a reference. It doesn't mean that the part will definitely not work well out of this range. Sometimes you do see the cases where LIR is out of this range.

    2. Please follow the equation in datasheet. Suggest to use resistors with 1% accuracy.

    Regards,
    Sam
  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 130 points

    Hi Sam

    IS it possible not to use with tow components, you suggest 6.8uH and 4.7uH, can i use only one 6.8uH for two outputs, What a disadvantage.

    Please suggest

  • 0 in reply to ilya feldman
    TI__Mastermind 19080 points

    Hi,

    It should be good. 0.2 to 0.4 is recommended but not a must.

    Regards,

    Sam