• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 903 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.

TPS7A88 / about Vout rise time

Tsukui Yusuke
Guru 21930 points
Other Parts Discussed in Thread: TPS7A88

Hi,

Could you tell me about TPS7A88 Vout rise time?
Customers want to Start up OUT1 and OUT2 at the same time.
・Condition：OUT1=1V, OUT2=3V

Datasheet shows the calculation formula of Tss.
However, Calculation of rise time is not described.
Please tell me how to calculate rise time.

Best Regards,
Yusuke/Japan Disty

  • 0
    TI__Guru 55940 points
    Yusuke-san,

    The soft-start equation that you mention is the rise time equation for Vout:

    tSSx = (VREF × CNR/SSx) / INR/SSx

    A feedforward capacitor can adjust this time slightly, with a bigger Cff increasing the startup time.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Guru 21930 points

    Ryan-san,

    Thank you for your support.
    Let me ask you one more thing.
    This formula does not take into account the output voltage.
    ◇tSSx = (VREF × CNR/SSx) / INR/SSx
    If the output voltage is different, I think that the rise time to change.
    Please tell me how to calculate the exact rise time of the output voltage.

    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru 55940 points

    Yusuke-san,

    Vout is a gained version of Vref.  The time for Vref to reach its final voltage is the same time for Vout to reach its final value unless a feedforward capacitor is used.  If a feedforward capacitor is used, there is an additional time while the feedforward capacitor charged.  This can be calculated as follows:

    tcff = 3R1 * Cff

    Very Respectfully,

    Ryan