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LTC4000 and DC/DC

m-kun
on Oct 23, 2018

Hi

I plan to use LTC3703 with LTC4000.(Back converter)

Condition is similar to below URL.  

https://ez.analog.com/power/f/q-a/99238/ltc4000/297154#297154

I have question  for ITH connection.

①LTC3703 have COMP pin for compensation.

　And DC/DC is required a control pin or external-compensation in LTC4000 datasheet.

　I think that ITH connect to comp pin.

　Is it right?

②LTC3703’s  compensation is TYPE1-3.

   That's different from Vc pin.(LT3845A)

   Are ITH required both CC pin compensation and TYPE1-3?

   Which connection is right   ITH-FB or ITH-COMP (below A or B?)

   

Best regards

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  • 0
    •  Analog Employees 
    on Oct 23, 2018 6:10 PM

    Hi

    The LTC3703 has an opamp for compensation rather than a high impedance transconductance amp, so the LTC4000 should be interfaced to control through the FB pin. The LTC3703 and LTC4000 will each require it's own compensation. The ITH output of the LTC4000 should be connected through an inverting buffer, and a resistor in series with the buffer output can be used to limit the range of control of the LTC4000.

    Regards

    David

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  • 0
    •  Analog Employees 
    on Oct 23, 2018 6:10 PM

    Hi

    The LTC3703 has an opamp for compensation rather than a high impedance transconductance amp, so the LTC4000 should be interfaced to control through the FB pin. The LTC3703 and LTC4000 will each require it's own compensation. The ITH output of the LTC4000 should be connected through an inverting buffer, and a resistor in series with the buffer output can be used to limit the range of control of the LTC4000.

    Regards

    David

Children
  • 0 on Oct 24, 2018 4:08 AM in reply to dkb

    Hi David 

    Thanks a lot .

    I see. LTC3703 ErrAmp is voltage amp.

    ILTC4000 will be interfaced to control through the FB pin(LTC3703).

    I have more question about

    " The ITH output of the LTC4000 should be connected through an inverting buffer, and a resistor in series with the buffer output can be used to limit the range of control of the LTC4000.".

    Which component do you mean about inverting buffer ?

    (R1? or R2? in LTC3703 page 8 or additional series resistor between ITH(LTC4000)

    to FB(LTC3703)?)

    About compensation, 

    We have compensation information (transfer function etc in datasheet) each IC(LTC4000 and LTC3703).

    I think there are mutual effect  ,specially CC .

    Are each IC compensation  enough for design?

    Best regards

    M-kun

  • 0
    •  Analog Employees 
    on Nov 1, 2018 12:06 AM in reply to m-kun

    Hi

    You can use almost any op-amp configured as an inverting buffer. I would compensate the LTC3703 circuit without the LTC4000, and then connect the LTC4000 circuit and follow the guidelines in the LTC4000 datasheet to compensate the overall loop.

    Regards

    David