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UC2843A: What device is never operating at 100% duty?

Yoshwa
Expert 4050 points
Part Number: UC2843A
Other Parts Discussed in Thread: UCC28051, UC2844A

Customer wants to design some application using such as UC2843A.

His main target is to keep out of 100% duty operation for any load conditions.

I think that UC2843A has the possibility of 100% duty.

As the result, customer inquiries what controller takes place of UC2843A.

What device can operate to keep out of 100% duty?

Is UCC28051 a corresponding one?

I appreciate your information which device is recommended to operate keeping out of 100% duty.

  • 0
    TI__Genius 9130 points
    Yoshwa-san,

    When you say that the customer wants to avoid operating at 100% duty cycle, what is the max duty cycle limit they require?

    There are 2 other devices in this family that limit duty cycle to 50% max - UC2844A and UCC2845A - are they suitable for the customer?


    It is also possible to limit the duty cycle close to but less than 100%, by adjusting the RC values on the RTCT pin. The internal oscillator produces a sawtooth waveform with 1.7 V pk-pk amplitude. The internal discharge path will discharge the CT cap by 1.7 V using 8-mA current sink, so a larger cap will take longer to discharge, and will set a longer deadtime before the next cycle can start. This allows the deadtime to be made larger (by using larger CT and smaller RT), and thus the duty cycle can be limited close to but less than 100%.

    The values depend on the desired Fsw, Dmax, etc.


    Thanks,
    Bernard