• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 64 subscribers
  • Views 460 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.

Original question:

CSD97394Q4M: 100% duty cycle operation

CSD97394Q4M: How to use CSD97394Q4M

William Leung
Prodigy 50 points
Part Number: CSD97394Q4M

Does CSD97394Q4M control the Vout by changing the duty cycle of PWM? Just Vout=Vin*PWM?

  • 0
    TI__Mastermind 24075 points

    Hello, 

    In buck converter,  Vout is almost equal to Vin*D, D is the PWM duty circle. 

    To regulate Vout accurately, a control loop is needed. 

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Prodigy 50 points

    Thank you for your reply, i have another question
    I want to use two CSD97394Q4M to drive with H-bridge.

    One PWM Pin input to control the H-FET switch. Can the other  PWM pin pulled  high all the time and keep the L-FET on?


    Thanks

  • 0 in reply to William Leung
    TI__Intellectual 800 points

    Hi,

    You may use CSD97394Q4M in a Half-Bridge configuration. However, please be aware input PWM pin has 3 signal levels:

    -If you apply PWM- High level, is will turn ON HS Fet and turn OFF LS Fet

    -If you apply PWM- Low level, is will turn OFF HS Fet and turn ON LS Fet

    --If you apply PWM-tristate level, ( between 0.9V to 2.2V) is will turn OFF both HS and LS Fets.

    Best regards,

    Lucian 

  • 0 in reply to Lucian Hriscu
    Prodigy 50 points

    Thanks for your reply, can I understand it this way:
    When I use two CSD97394 to use the H bridge, follow these steps
    1. Pull two PWM pins to low level and set two SKIP # to tri-states
    2. When ready to drive the load, pull the two SKIP # to low level and keep it at least 50us
    3. Then, two PWMs are introduced to drive the H-bridge?

    Looking forward to your reply

  • 0 in reply to Qian Chen
    Prodigy 50 points

    Thanks for your reply, and one more question:
    When the SKIP # Pin needs to be pulled low and lasts for at least 50us,

    is it possible to keep the PWM pin in a tri-state, and then introduce PWM again,

    or when the SKIP # is pulled low by 50us, the PWM pin must also be pulled low. level?

    THANKS
    Looking forward to your reply

  • 0 in reply to William Leung
    TI__Intellectual 800 points

    William,

    SKIP # pin on the CSD97394Q4M enables the Diode Emulation function in sync Buck converter. If you held SKIP# pin low, internal current zero crossing detector is enabled for the LS FET. At light load, if Inductor current zero-cross 0A it will turn turn-off LS FET and you can operate in DCM mode. In this state HS FET is OFF, LS channel is OFF and LS body diode is freewheeling load current.It was designed to improve light load buck converter Efficiency.

    PWM input signal is not related to SKIP# signal.

    A high PWM level turns on HS Fet, a low PWM level turns ON LS Fet. CSD97394Q4M introduces a small 5..8nS dead -time in between HS and LS Fets.

    In your case, if you pull SKIP# pin is pulled low for 50uS, the part is Enabled for DCM mode. Not sure what benefits you see on a Half-bridge converter. During this 50uS window, you can drive PWM input High, low or tri-state depending of your needs.

    For a Half-bridge CCM mode operation  I will simply held SKIP# =5V and drive a TTL signal level on PWM pin . Please also note there is a small hold-off delay on both SKIP# and PWM inputs. This delay was introduced to prevent parasitic tripping on noisy signals.

    Best regards.

    Lucian

  • 0 in reply to Lucian Hriscu
    Prodigy 50 points

    Thanks Lucian, I got it.

    Best regards.

    William