• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 4 answers
  • Subscribers 62 subscribers
  • Views 151 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.

UCC25800-Q1: OCP1_6 Setting, tolerance

Patrick Ruf
Genius 4820 points
Part Number: UCC25800-Q1

Tool/software:

Hi,

I like to choose OCP1_6 OCP setting for the UCC25800-Q1. This with Ra=Rb (as of Maximum dead time selection). Resistors should be out of E24. So I have chosen Ra=Rb=5.1k. But with this I'm right at the edge of Rth=2.55k.
Even with a 0.1% resistor Rth can be out of OCP1_6 range. How strict are those ranges in table 8-1 since the distance to the OCP1_5 area (Rth = 4.9k ~5.1k) is quite large?
I know this question is a bit weird as ranges are ranges but with E24 resistors it is a bit hard to be right in the range (best case in the middle of the range).

Best regards,

Patrick

  • 0
    TI__Guru 54215 points

    Hi,

    Ra = Rb does not give max dead time. Please follow Fig 8-9 to get the max dead time which requires the OC/DT voltage between 0.5V and 1.0V. 

    For OCP1_6, Ra//Rb needs between 2.45k and 2.55k.

    You would need to play with the each resistor values to find out. For example, Ra = 18.2k, and Rb = 2.94k, E96, give

    OC/DT = 0.695V, between 0.5V and 1.0V 

    Ra//Rb = 18.2k//2.94k = 2.53k, between 2.45k and 2.55k

  • 0 in reply to Hong Huang
    Genius 4820 points

    Hi,

    Sorry, my fault. I wanted to write maximum dead time selection of around 100ns.

    Regards,
    Patrick

  • 0 in reply to Patrick Ruf
    TI__Guru 54215 points

    Hi,

    I am not understanding what do you mean" to write maximum dead time ....".

    You need to follow the steps to get what you need for dead time by the voltage based on Fig 8-9 while still able to keep Ra//Rb in 2.45k to 2.55k.

    This is simple but need you to play with Ra and Rb values to keep their parallel result in the range while make dead time as big as possible. As 2.45k and 2.55k are not much different, so you may not get very different dead time.

  • 0 in reply to Hong Huang
    TI__Guru 54215 points

    Hi,

    I am not understanding what do you mean" to write maximum dead time ....".

    You need to follow the steps to get what you need for dead time by the voltage based on Fig 8-9 while still able to keep Ra//Rb in 2.45k to 2.55k.

    This is simple but need you to play with Ra and Rb values to keep their parallel result in the range while make dead time as big as possible. As 2.45k and 2.55k are not much different, so you may not get very different dead time.

    Actually 4.99k // 4.99k, E96 gives 2.495k - so meet your need. E96 is 1% so no need to use 0.1% tolerance resistors.

  • 0 in reply to Hong Huang
    Genius 4820 points

    Hi,

    I need a maximum deadtime  (DTmax) of 100ns. Therefore Ra=Rb (VOC/DT=2.5V). We can only use E24 resistors. So the closest I get for OCP1_6 OCP is Ra=Rb=5.1k.
    So my question is: Is the range 2.45k ~ 2.55k a nominal range for Rth or do I have to be strict within this range (including resistor tolerance)?

    Regards,
    Patrick

  • 0 in reply to Patrick Ruf
    TI__Guru 54215 points

    Hi,

    If only E24 resistors can be used, then make Ra = 10k//10k = 5k, and Rb = 10k//10k = 5k, then it is ok.