• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 64 subscribers
  • Views 311 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.

TPS92692-Q1: DIM/PWM CONTROL & SWITCHING FREQUENCY QUESTION

HYUNCHUL LIM
Prodigy 30 points
Part Number: TPS92692-Q1


Please understand that my English is poor.

I designed the circuit as follows in the application notes, but I have some questions about the circuit.

Thanks for the help.

\\\\

Q1_2.pdf

  • 0
    TI__Mastermind 18890 points

    Hello Lim,

    Answer 1:  With R14 at 249K we expect the input to DIM/PWM to be either 3.3V or 0V for PWM dimming.  We do not expect you to vary this voltage as you are doing.  So please input this with 3.3V for 100% PWM dimming.  Also change R13 to 10K to give some filtering to the input of DIM/PWM.  Note:  Your PWM dimming FET Q1 is connected backward with the Drain and Source.

    Answer 2:  The Frequency change is due to the spread spectrum frequency modulation feature of the part for EMI.  Please read section 8.3.3 of the data sheet where we explain out this and the +/-15% variation of the frequency to reduce EMI.  As for the glitch that you are seeing:  There will always be some glitch depend on your layout and scope ringing.  Please make sure that the GATE trace is short to the FET Q2.  You can also add snubber circuit to slow down the switching edges with a capacitor and resistor from the Drain of Q2 FET to ground.  Only add snubber if you have issue with the ringing causing you EMI issue because it will reduce efficiency of the regulator.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Prodigy 30 points

    very thank you for your response.. it helped me much.

    there is a additional question.

    question1-1 for answer1 :At R14 249K, external PWM (0V OR 3.3V NOT VARING) only affects ON/OFF of Q1 and is independent of Q2`s on/off?

  • 0 in reply to HYUNCHUL LIM
    TI__Intellectual 1675 points

    Hello Lim,

    We are working on this and will get back to you within 24 hours.

    Best Regards,

    Caroline

  • 0 in reply to Caroline Fuschino
    TI__Mastermind 18890 points

    Hello Lim,

    With DIM/PWM at 3.3V it will be 100% dimming which means continuous switching with Q2 and Q1 is ON.  With DIM/PWM at 0V it will shut both Q1 and Q2 off.  Please read section Direct PWM Dimming in section 8.3.10.  You need to familiarize yourself with PWM Dimming means.

    Note that you we expect some frequency on PWM dimming like 200Hz to 2KHz.  You can pull it high for continuous ON but cannot use that pin as an OFF control of the regulator. 

    Thanks Tuan