• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 65 subscribers
  • Views 244 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TPS22990: Calculation of CT capacity

user201583
Prodigy 140 points
Part Number: TPS22990

Dear Sir or Madam,

I am trying to determine the value of CT using Equation 1 of the data sheet (JAJSCB8C) to adjust the rise time of TPS22990.
However, the data sheet (JAJSCB8C) says “An approximate equation ... when VBIAS is set to 5 V”.
Is it possible to use Equation 1 as it is when using at VBIAS = 3.3V?
Redards,
Hasegawa
  • 0
    TI__Guru** 105211 points

    Hi Hasegawa,

    Thanks for reaching out!

    We will check and get back to you shortly.

    Best Regards,

    Rakesh

  • 0
    TI__Genius 15740 points

    Hi Hasegawa,

    When VBIAS = 5V and VBIAS = 3.3V, the rise time is slightly different. This comparison can be seen in figures 17 and 18.

    In your design, what input voltage is being used? In general, VBIAS = 5V and VBIAS = 3.3V will have similar rise times for lower voltages, but it will vary a bit more once VIN = VBIAS.

    Thanks,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Prodigy 140 points
    Hi Alek-san,
    Thank you for your response.

    My design is VIN = VBIAS = 3.3V.

    There are several DC / DC converters after the TPS 22990.
    The sum of their input capacities is about 100 uF, and I think that this value corresponds to CL.

    If the rise time is affected by CL, I would like to know the formula of rise time including CL.
    Regards,
    Hasegawa
  • 0 in reply to user201583
    TI__Genius 15740 points

    Hi Hasegawa-san,

    We have some data for VIN=VBIAS=3.3V, and using this data I was able to come up with the following equation:

    tR(us) = 0.0372 x CT(pF) + 23.41

    Load capacitance does not have a large effect on rise time, so this should be a good estimate even for 100uF CL.

    Thanks,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Prodigy 140 points

    Hi Alek-san,

    Thank you for your reply.

    I would like to refer the answers to the design.
    Best regards,
    Hasegawa