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UCC3808A-1: Voltage mode

Part Number: UCC3808A-1
Other Parts Discussed in Thread: UCC25600, UCC38083, UCC28230

Hello!

I'm looking for a "voltage mode" controller in "8 pin solution" push pull configuration for half bridge smps but "not LLC" like ucc25600. I not found this controller, only current mode. There's a such controller? 

It's possible to configure UCC3808A or UCC38083 family in voltage mode?

Thanks and regards

Cristian

  • Hi Christian,

    The UCC28230 is a 14 pin device that is a closer match to what you want, www.ti.com/.../ucc28230.

    Alternatively you can run the UCC3808A in voltage mode by putting the oscillator pin through a simple emitter follower buffer circuit into the CS pin. The datasheet for the UCC28C4x family shows this circuit on page 21, figure 28, www.ti.com/.../ucc28c43.pdf.

    Regards

    Peter
  • Hi Peter!

    Thanks for your answer. I've another 3 questions:

    1) Using ucc3808a in voltage mode like fig.28 can I keep also the current protection on CS pin from external circuitry? I read primary current of both switch on half bridge with a sense transformer sending information on Cs pin with a small low pass RC filter.

    2) And with ucc38083 it's possible to put it in voltage mode? I'm thinking to use Iset current (slope compensation) as fixed ramp on CS pin just before 0.3V pwm comparator, keeping also current protection. What do you think about?

    3) This could be a crazy design: If I use ucc25600 avaiable in my lab. as fixed frequency but modulating continuosly dead time pin in order to change duty cycle, what do you think about? Between 150 and 200 khz I should have duty of 0.28/0.5 for each out. Could DT pin burn?

    Regards

    Cristian
  • Hi Cristian,

    Its outside our normal area of experience, I guess you can try run mostly in voltage mode say 80% or 90% with the remainder coming from the CS circuit and see if the system behaves itself.

    The UCC25600 sounds like an interesting and alternative approach. There should be no problem with the reliability of the DT pin provided the ratings are respected.

    Regards

    Peter