• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 738 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.

UC3825B: Understanding Datasheet Parameter of PWMI IC

Arumugam Rajendran39
Prodigy 200 points
Part Number: UC3825B

I am trying to derive the Transfer Function and Gain of PWM Modulator. Could any one please explain me how the Ramp is generated in PWM IC ? Why the 1.25V DC Offset is introduced in Ramp? In datasheet, Ramp valley Voltage is given as 0.7 V, How is it possible with 1.25V fixed offset?

I need the parameters which I indicated it in figure, Please someone help me to extract those parameters,. (Consider  Fsw: 180KHz, Dmax = 0.35)

 

  • 0
    TI__Expert 4015 points

    Arumugam, can you post a link to the datasheet you are using. I do not see the diagram you show on the TI datasheet.

    Thanks

    Billy

  • 0 in reply to Billy Long
    Prodigy 200 points
    Billy,
    Please go to this link
    www.ti.com/.../uc3825b.pdf

    The Ramp ( figure ) which I shown above in not in datasheet, however I need this parameters ( Ramp Valley , Ramp Peak, Offset, d1, d2 ) for doing Simulation. I don't know How to extract those parameters from the datasheet and there is no information in the datasheet regarding the ramp generation.

    Could you please, How it is generated ? Why the DC offset is included? and more particularly how to extract those ramp parameters from the datasheet (Assume : F = 180KHz , D = 0.35) ?

    Please explain the oscillator section of datasheet.

    Thank you Billy,

    Regards,
    Aaru
  • 0 in reply to Arumugam Rajendran39
    TI__Expert 4015 points

    Aaru, figure 8 shows how the ramp is generated depending on whether you are operating in current mode or voltage mode.

    The offset is presumbaly to ensure that the the PWM comparator input is within the dynamic range of the op-amp.

    In voltage mode the Ramp voltage will be the oscillator voltage + 1.25V as shown in Figure 8. The oscillator ramp and valley voltage are specified in the electrical table.

    In current mode the ramp will depend on the switch current and sense resistance.

    Thanks

    Billy

  • 0 in reply to Billy Long
    TI__Expert 3200 points
    Hi Arumugam,

    I see you asked for similar information on LinkedIn. I hope the answers are helpful but if not let me know.