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TPS61170-Q1: Ip and Iout_max calculations (Page 17)

Juha Pajunen
Prodigy 60 points
Part Number: TPS61170-Q1

Tool/software:

Hi,

https://www.ti.com/product/TPS61170-Q1/part-details/TPS61170QDRVRQ1

There is a equations on page 17 of Datasheet: 8.2.1.2.2 Maximum Output Current

Do you have a example calculation for Ip and Iout_max calculations?

I am getting Ip=0.32A and Iout_max 1A with an example values and my resulra differs what is on datasheet.

Ip = 1/(10*1,2*(1/(12+0,2+5)+1/5)) = 0.32A

Iout_max = =12*(1,2-0,32/2)*0,95 / 12 = 0.99A

Are those ok?

Sincerely,

--Juha

  • 0
    TI__Guru 65390 points

    Hello Juha,

    Could you please add the units to your calculations? With just the values, it is hard to follow your calculations.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 60 points

    Hi,

    Ip = 1/(10uH*1,2MHz*(1/(12V+0,2V+5V)+1/5V)) = 0.32A

    Vin=5V

    L=10uH

    Vf=0.2V

    Fs=1.2MHz

    Vout=12V

    Iout_max = 5V*(1,2A-0,32A/2)*0,95n / 12V = 0.41A

    Vin=5V (I had a error on this - was 12V should be 5V)

    Ilim=1.2A

    Ip=0.32A

    n=95% (Efficiency)

    Vout=12V

    Used values should be the same as on example on page 16.

    --juha

  • 0 in reply to Juha Pajunen
    TI__Genius 15210 points

    Hi Juha,

    Expert for this device is out of office. Please expect a reply next week.

    Regards,

    Mulin

  • 0 in reply to Juha Pajunen
    TI__Guru 65390 points

    Hello Juha,

    In the Ip formula, you have 12V+0.2V+5V and this should be 12V+0.2V-5V. So I would then get about 250mA.

    When I then take an efficiency of 90% which is more realistic according to figure 17, the output current is in the range of 400mA.

    But this is only valid as typical value and I expect that the person giving this result wanted to be more on the save side, e.g. for the switching frequency and the current limit, you should use the minimum values and not the typical values to make sure that the output current can be achieved for all components and not just typical ones.

    So as an estimate, I think 300mA is ok.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 60 points

    Hi,

    Ok thank you for correcting my formula and calculations.

    --juha