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UCC28C44: If there is any risk when customer wants to use 5.1kohm RT resistor.

Gary Zeng
Intellectual 1145 points
Part Number: UCC28C44

Tool/software:

Hi team,

My customer wants to use UCC28C44 in power project.

Q1: They want to know if there is any risk when they set RT resistor to 5.1kohm.

RT resistor is relevant to the charge of CT capacitor. And discharge current is stable as 8.4mA in datasheet. The ratio of charge and dischage is also relevant to maximum duty cycle. We know the maximum duty cycle is 50% for UCC28C44.

Q2: What is the detailed relationship between RT/CT and duty cycle.Is there a min and max limitation of RT? Why？

  • 0
    TI__Expert 7473 points

    Hey Gary,

    Thanks for reaching out with interesting questions.

    Gary Zeng said:
    Q1: They want to know if there is any risk when they set RT resistor to 5.1kohm.

    No risk. In fact in the datasheet you can see the graph for RT from 1k to 100k (Figure 6-1) for different CT values.

    Gary Zeng said:
    Q2: What is the detailed relationship between RT/CT and duty cycle.Is there a min and max limitation of RT? Why

    For the lowest RT and highest CT, you will have min duty cycle.

    For the highest RT and lowest CT, you will have max duty cycle.

    There is no max limitation on RT as such but there is definitely a min limitation on RT which should be at least 1k, if not there will always be a current slow charging the CT and never fully discharge it.

    Hope this help. Please click on the green button if this resolves the issue. If not, feel free to ask more.

    Best,

    Pratik A.