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TPS92511: What is ton in equation 4 in the device datasheet?

Kazuya Nakai59
Guru 20780 points
Part Number: TPS92511
Other Parts Discussed in Thread: TPS922052

Hello guys,

One of my customers is considering using TPS92511 for their new products.

At this moment, they have the following question.
Could you please give me your reply?

Q.
They want to calculate inductor value using equation 6.
The equation 6 uses the value of "2 * delta * IL1".
This "2 * delta * IL1" can be calculated with equation 4.

The equation 4 uses "ton" parameter.
What is "ton" in equation 4?
Is this "ton" the minimum on-time (Typ250ns, Max400ns) in the electrical characteristics on page 5 of the device datasheet?
Also which value is better to use? 250ns or 400ns?

Your reply would be much appreciated.

Best regards,
Kazuya.  

  • 0
    TI__Mastermind 19685 points

    Hi Kazuya,

    t_on refers to the switching-on time of the integrated MOSFET (Please refer to Figure 13 from the datasheet.).

    You can estimate t_on with t_on = 1 / f_SW * Duty = 1 / f_SW * V_LED / V_IN / efficiency. When you design the components at the first time, you can estimate a value for the efficiency (like 90%) and use that for calculation. You can later adjust the components based on your test results.

    The t_on(min) shown in Section 6.5 Electrical Characteristics from the datasheet refers to the switching minimum on-time. You should choose the switching frequency based on the switching duty of your application and make sure you switching-on time t_on is higher than t_on(min) if good line and load regulations are required.

    I would recommend customer switch to our newer device TPS922052/3/4/5 for its better performance.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Guru 20780 points

    Hi Steven,

    Thank you very much for your reply.

    I understood it.

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 19685 points

    Hi Kazuya,

    You are welcome. I am going to close this thread. Please feel free to contact me again if you have any further question.

    Best Regards,

    Steven