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TPS61073 - Choosing correct inductor value

MarcosCba
Prodigy 140 points
Other Parts Discussed in Thread: TPS61073

Hi! I’m using the boost converter TPS61073 for generating 5V, 110mA from a single-cell Li-Ion battery. The battery voltage can vary between 3 and 4,2V depending on the battery charge (The battery capacity is 850mAh). So for choosing the components I used the formulas given in the datasheet:

R1=R2*(VO/vFO -1)

·      VFB=500mV (from datasheet)

·      R2=180KΩ  (from datasheet)

·      Vo=5V (project requirement.)

So R1=1,62 MOHM

For choosing the inductor I supposed 2 conditions depending on the battery charge:

First condition

·         Vbat= 3V (battery discharged)

·         I=110mA

·         Vo=5V

IL=IO(VO/(VBAT*0,8))

So IL= 230mA

L=(VBAT*(VO-VBAT))/(f*IL*0,4*VO))

Supposing the ripple current in the inductor 40% ΔIL and f=1200KHz:

So L=10,9uH

 

Second condition:

·         Vbat= 4,2V (battery fully charged)

·         I=110mA

·         Vo=5V

·         Supposing the ripple current in the inductor 40% ΔIL and f=1200KHz:

IL=164mA

L= 8,55uH

So which inductor should I chosee?? The datasheet also states that the device has been optimized to operate with inductance values between 2.2 μH and 10 μH. So Choosing an  10uH inductor  will be the right choise?

What happened if I choose the 8,55uH inductor??

 Thanks in advance!

  • 0
    TI__Mastermind 36110 points

    There will be very little difference in functionality with an 8.55uH (not a standard value) and a 10uH inductor.  My suggestion is that you evaluate performance using the circuit provided by the EVM.  I am confident that this will give you good performance and you can use the EVM component values.  It is CRITICAL that you follow the EVM layout guidelines when you layout your PCB.  All switching power supplies require very specific layout techniques to ensure proper operation. The EVM layout has been built and tested, so please follow it exactly.

  • 0 in reply to Matthew Day
    Prodigy 140 points
    Okay! Thank you very much Michael!
  • 0 in reply to MarcosCba
    Prodigy 50 points

    @marcos - is your design working ?

    My IC is getting too hot and not giving 5V output. Its just giving 3.4V of output. 

    What is the voltage that you are giving to enable pin ?

    Thanks

  • 0 in reply to sachin kumar1
    Prodigy 140 points

    Hi Sachin,
    Yes my project works great! The booster gives me the 5 volts for any input between 3V to 4,4V and it do not get hot; But it was a long time ago since this project, so i really don't remember much of it.
    What I remember is that the desing of the PCB is very important, you must follow the advice given in the datasheet, or at least try to meet most of them.
    I'm sending attached the schematic of my design maybe that can help you. Also the PCB design.
    Let me know if this help you, or you need further help7774.TF_Final.pdf

  • 0 in reply to MarcosCba
    Prodigy 50 points

    Hello MarcosCba,

    Thanks a lot for your response. My project is exactly the same as your.

    Do you have PCB design files because I opened the pdf you send and its i guess in Spanish which i can not understand ?

    The design files will a lot of help.

    Thanks a lot.

    regards,

    sachin

  • 0 in reply to sachin kumar1
    Prodigy 140 points

    Yes, is spanish, I'm from Argentina... But the text you see there is about other PCB of the same project, so don’t pay attention to it

    See the attached. This PCB was designed on "Protel 99SE versión 6.6.7 service pack 6." So maybe you’ll need that software to open it.

    Hope it helps!

    0741.PCB.rar

  • 0 in reply to sachin kumar1
    Prodigy 50 points

    Thanks MarcosCba for your help.

    I'll try to use your advise.