• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 307 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.

TPS7A33 Soft-Start Capacitor Programming

Joel Mock
Prodigy 130 points

I am using a TPS7A3301RGWT Negative Linear Regulator in a circuit with a -17V input and -15V output.  Circuit almost identical to evaluation board circuit.  Using a soft-start capacitor = 1uF.  Per page 10 of data sheet output settles within 40ms.  In my circuit settling takes 1.6seconds.  When I remove the soft start cap - regulator output stabilizes to set point per data sheet (about 40 - 50ms).  Any thoughts?  Thanks!

  • 0
    TI__Guru 55940 points

    Hi Joel,

    The line transient graphs in the datasheet were taken without a Css.  This is why when you remove the cap you match the datasheet.  There a few different knobs you can turn to affect the transient response.  In general you will either reduce the magnitude of the transient while allowing the duration, or decrease the duration while permitting a larger magnitude.  

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 130 points

    Ryan:

    Thanks. It would appear that page 10 of the data sheet suggests that the data was taken with a Css = 1uF?  Is that correct?

    Joel

  • 0 in reply to Joel Mock
    TI__Guru 55940 points

    Hi Joel,

    Figure 27 in the datasheet appears to have an error.   The startup equation for this device is:

     tstartup=1,200,000*Cnr. Where tstartup will be in seconds and Cnr is in farads.

    We will update the datasheet to correct the error and add the equation.

    Very Respectfully,

    Ryan