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UCC28950: About Minimum Pulse (TMIN)

Ryu Yamashita
Genius 3600 points
Part Number: UCC28950

Hi team,

I checked 23p of the datasheet and found the following formula for TMIN.
TMIN =(5.92 * Rns)
Does this 5.92 vary depending on the device?
If it can vary, please let me know the minimum value.

Sincerely.
Ryu.

  • +1
    TI__Guru* 85616 points

    Hello,

    The data sheet has specification for Tmin that give the tolerance of that function.  Please refere to page 8 of the data sheet.

    Regards,

    Mike

  • 0 in reply to Mike O'
    Genius 3600 points

    Hello,

    The data sheet shows a resistance value of 88.7kΩ, and when I recalculate, the coefficient of 5.92 is 4.79 at minimum.
    Is it correct that this is the same when the minimum value of 10kΩ is connected?

    Sincerely.
    Ryu.

  • +1 in reply to Ryu Yamashita
    TI__Guru* 85616 points

    Hello,

    This RT pin programs a current mirror.  This current mirror generally charges and internal capacitor.  The variation of the current mirror ration and the internal capacitor should be roughly +/- 19 %.  This variation does not take into account RT resistor tolerance.

    Regards,

    Mike

  • 0 in reply to Mike O'
    Genius 3600 points

    Hello,

    Thanks for reply.
    I understand. I have an additional question.
    On p23 of the datasheet, it says that RTMIN can be connected to 10kΩ or more, but on p5, it says that the minimum recommended value for TMIN is 100ns.
    If I connect 10kΩ, I think the value will be less than 100ns, which should I follow?

    Sincerely.
    Ryu.

  • +1 in reply to Ryu Yamashita
    TI__Guru* 85616 points

    Hello,

    I see that you are correct that with a 10 k ohm resistor RTmin will be set to 50 ns and not 100 ns.  Figure 30 of the data sheet.   There is characterized data for 10 k so the device should work with 10 k.   However, if you want 100 ns you can increase the RTmin resistance to get increase it to 100 ns. So it is up to you what you set this too.  Most customer chose to set it to 10 k and have not had issues.

    Regards,