• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 340 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS54202: Inductor sellection

Takashi Yamaguchi
Genius 13490 points
Part Number: TPS54202

Hi team,

My customer would like to use the TPS54202 for the following condition. Could you let me know the recommended inductance value and how to calculate?

Vin : 10V to 20V

Vout : 3.3V

Iout : 20mA

According to the equation 8 in the d/s, the inductance would be 842uH(min) at the customer's condition.  On the other hand, Webench recommends 220uH (189.1uH to 378.1uH). I don't think that this design requires such a large inductance. I believe that the equation 8 is for CCM.

Anyway, could you let me know the recommended inductance and its equation?

Regards,

Yamaguchi

  • 0
    TI__Genius 10070 points

    Hi,

    The output current Iout in equation 8should be 2A, it is the max output current of the device, not the load current.

    L=(3.3*(20-3.3))/(20*0.3*2*500k)=9.2uH.

    Shawn

  • 0 in reply to Shawn Nie
    TI__Genius 13490 points

    Hi

    Thank you for the answer. I explained it to customer, but I received following additional questions. Could you support this?

    1. The load current is only 20mA(max), but why does it need to use 2A? 

    2. Webench recommends 220uH (189.1uH to 378.1uH), why Webench recommends such a large inductance?

    3. Customer would like to have high efficiency at 20mA. In that case, should customer use larger inductance? Is there upper limit for the inductance? What inductance can achieve high efficiency? 

    4.  Could you tell me how does pulse skip mode work? For example, SW turns on for Ton(min), then turns off sw until inductor current reaches 0A. 

    5.Could you let me know how to calculate the inductor ripple current at pulse skip mode?

    Sorry to the many questions.

    Regards,

    Yamaguchi

     

  • 0 in reply to Takashi Yamaguchi
    TI__Genius 13490 points

    Hi 

    Could you support the questions?

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Genius 10070 points

    Hi Yamaguchi,

    Sorry for the delay, it is Chinese National Day, I am just back to the office today. 

    1. This equation is used to calculate L, it is related to the inductor ripple, usually the inductor ripple should be 10%-40% of max output current, or the system is easy to be interfered by the noise.

    2. Webench use the wrong equation, we will correct it.

    3. For this device, the efficiency is already high because it work in Eco-mode at light load, what the efficiency does the customer want?

    4. You can refer to below app note to understand Eco-mode.

    5. The Eco-mode is a litter complicated, and it is decided by COMP voltage there is no accurate equation to calculate it.

    Shawn