• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 161 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.

LM3550: Time limit tollerance

Ben Strawbridge1
Prodigy 240 points
Part Number: LM3550

Hello,

I am seeing a fairly large time limit tolerance and just checked the datasheet. the only detail I can see is for the switching frequency - approximately -12% / +15% 

Is there a defined tolerance on the on time limit clock? is this the same as above or is it differnt?

The variance I am seeing at the moment is with a 512ms limit set the IC can stop as early as 488ms (~10%) and possibly sooner. (I have never tested for the ability to run longer) 

Kind regards,

Ben Strawbridge

  • 0
    TI__Mastermind 22745 points

    Hi Ben,

        Yes, the switching frequency is determined by the internal clock and it has the same tolerance with this switching frequency which covers the whole tolerance for the full process tolerance and whole supply voltage range.  And this tolerance doesn't have much effect on the application since for such kind of LED driver, you may more focus on the current tolerance. 

    BR

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 240 points

    Hi Sean,

    thank you for confirming this.

    It does have an impact on applications though as the device allows the setting of a on time limit of up to 512ms, however with this tolerance i believe the longest guaranteed on time is actually 440ms which could cause issues for people using this device.

    It is also worth noting as this is not obvious if people are setting a shorter time limit and having issues the same tolerance applies and so they will have to select a time limit well above their maximum desired on time

    Kind regards,

    Ben Strawbridge