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Integrated FET UCC28730 "zero power" flyback controller

Keith Keller
Expert 7600 points

Other Parts Discussed in Thread: UCC28730, UCC24650, UCC28910

Hello,

What is the expected regulation tolerance of the UCC28730  NOT using the UCC24650?

Is there a plan to release a UCC28730 “zero power” flyback controller with an integrated FET like UCC289xx?

Thank you, Keith

  • 0
    TI__Guru* 86286 points

    Hello Keith,

    The PSR controller's are generally +/-5% in accuracy.  The UCC24650 wakeup chip will reduce the output capacitance required by a factor of 6.5 due to the faster transient response.  I think this is bigger selling feature compared to the 0 power.

    If you don't use the wakeup chip you have to size your output capacitor to handle a transient response based on 32 Hz.  I would not recommend using this PSR controller without the wakeup chip. 

    You could use the UCC28910/1 devices that have integrated FETs, that don't require the wakeup chip.

    At this time I don't believe the product line plans on developing a version of the UCC28730 with an integrated FET.

    However, I will mention it to the product line.

    Regards,

    Mike

  • 0 in reply to Mike O'
    TI__Genius 15910 points
    Hi Keith, when testing the EVM without the UCC24650 biased, my output dropped to somewhere around 1V with a transient from 0A to full load. Keep in mind that my output caps were sized for working with the wakeup chip (so considerably smaller than "normal") and my transformer was designed for low switching frequency at no load to showcase the zero-power chipset. Hope this helps.
  • 0
    TI__Expert 7395 points
    Keith,
    the wakup chip UCC24650 doesn't affect DC voltage regulation or even transients when in steady state. It comes into play when the UCC28730 enters stanby mode(and lowers its switching frequency very low). If a transient occurs in this standby mode, that's where the wakeup chip serves to assist with transient performance.

    As this is the external forum i will not discuss product roadmap here. If you would like to discuss that please post internally.

    Regards,
    John
  • 0 in reply to John Stevens
    TI__Expert 7600 points
    Hello,
    Thanks so much for all the help. The customer has some additional questions:

    The customer is running off of a battery voltage ranging from 45 - 130Vdc and the solution does NOT need to be isolated.
    So instead of using the UCC24650, they will directly tie Vout to the VS sense pin 2 on the controller.
    #1 Do you see any issue with configuration the IC in this way?

    #2 Is there any concern with running a flyback converter off of a DC supply, versus a standard AC input?
    I don’t think so, but the customer wanted me to double confirm.

    #3 Is there any concern with running the UCC28730 as low as 45Vdc?
    The UVLO is specified worst case over temperature from 7 – 23V, so I do not think there is an issue. Also double confirming.

    Thanks very much. Keith
  • 0 in reply to Keith Keller
    TI__Genius 15910 points

    Hey Keith,

    1. The VS pin does a whole lot more than just regulate the output voltage. Its top priority is to monitor the scaled down version of the DRAIN waveform to determine the demagnetization point of the transformer, so tying this pin directly to the regulated output voltage wouldn't work  well, an auxilliary winding is needed so that the signal on VS looks like what is shown in Figure 14 of the UCC28730 data sheeet. 

    2. and 3. are sort of related; No concern with using a DC supply as long as HV can supply enough current for the internal current source to charge VDD.  The minimum voltage to start charging is around 20V on HV but the current needed is up to 500uA (max) for start up until VDD ramps up to UVLO.