• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 66 subscribers
  • Views 852 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.

UCx84xA Current-Mode PWM Controller

Monil Jadav
Prodigy 190 points

Hello,

Datasheet : www.ti.com/.../uc2843a.pdf

There are some unexpected calculations 

1) Page No. 11 Fig 8. wrong equation. corrected F = 1.72 / (RT*CT) if this is wrong eq. please provide right one.

2)Page No. 15 Eq 4 Cout value not matched for Fc = 2.5Khz

3)Page No. 16 Eq.8 Lpm value not match.

Kindly provide right equations.

  • 0
    TI__Genius 9130 points
    Monil,

    You are correct:

    1) Page 11 Fig. 8 - the eqn should be f = 1.72 /( Rt * Ct) - this was correct on the previous version of the datasheet.

    2) This eqn has 2 errors - firstly, it should be calculated for an output voltage drop of 10% instead of 20% (to match the assumptions in the preceding text) - this gives a value of 1.333 mF. Secondly, it actually uses an estimate of 2 kHz for fc instead of the value of 2.5 kHz in the assumptions in the preceding text.

    3) This eqn has an error, the switching freq fsw should be included in the denominator. The correct eqn should be:
    Lpm >= (Vbulkmin * Dmax) / [((70% * Iout) / (n * Nps)) * fsw]
    In this example, assuming Fsw = 100 kHz, the calculated Lpm value is ~1.63 mH

    I hope this helps clarify the confusion in the equations.

    I will forward these points to the responsible team to get the datasheet corrected. Thank you for highlighting these errors to us.

    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    TI__Guru* 86286 points

    Hello Monil,

    I will work on getting this corrected.  Thank you for pointing this out to us.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 190 points
    Still it is not corrected.
  • 0
    Prodigy 200 points
    Hello,

    In the frame of a space appplication (Exomars2020 mission), we have selected this référence : UC1843J883B (5962-8670402PA) in CDIP-8 package.

    The maximum absolute rating (following the datasheet) is 30V. The question is to know how long time the component is able to support an overvoltage higher than 30V (two cases : 40V and 60V)

    So, Could you please help me to answer about this question?

    Many thanks
  • 0 in reply to Sadok Abbaki
    TI__Expert 4015 points
    Hi Sadok, TI does not guarantee any operation outside the specified Abs Max ratings.

    Per note (1) of the table,
    "(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
    only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
    Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability."

    If you are worried that the Vcc or other voltage may increase above the abs max I would recommend putting a clamp in to ensure that this doesn't happen.

    Thanks
    Billy