• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 305 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.

UCC28950: DELEF, REF value

Ross Parlour
Intellectual 1845 points
Part Number: UCC28950

Hi there,

Can I check why we recommend the value of REF for DELEF in the datasheet is 13KOhm - 90KOhm please?

I am trying to explain to a customer the reasons why he cannot use 10KOhm, other than it does not meet the datasheet spec. It would be good to understand the consequences of using a value below our recommended spec.

Apologies in advance, I also prefer just following the datasheet :).

Many thanks,
Ross

  • 0
    TI__Mastermind 25570 points
    Hello Ross

    There are two reasons -

    First, if a designer sets RDELEF to 13kOhm then the programmed delay will be about 28ns. Shorter delays than this are not really useable and in any case as the delay is shortened the body diode conduction time of the SR will increase leading to larger losses and lower efficiency. What the designer should be striving to do is to increase the delay so that the SR is turned off just before its current goes to zero thereby minimising losses in the SR. Of course, you cannot wait too long to turn the SR off because if you do the current in the channel will drop to zero then increase in the negative direction leading to a large voltage spike as the SR is turned off.

    Second - if the resistance is too low then there are long term reliability concerns for the circuitry inside the IC itself. There is of course a large margin between the specified lower limit of 13k and the point at which lower reliability becomes an issue.

    I'd be interested to know why they think that they need a delay time of less than 28ns.

    Regards
    Colin