LTC3779 use in non-synchronous buck-boost converter

Dear Analog team:

I select LTC3779 for my DC/DC converter, and my customer is asking me to design this IC in non-synchronous buck-boost converter.

Would you kindly answer my following problem, thank you!

1. Could LTC3779 design in non-synchronous buck-boost converter? If the answer is NO, please tell me why and what damage will cause if I design this structure.

2. Could LTC3779 design with isolate driver IC like adum3224? If the answer is YES, please kindly share how to design the circuit, If the answer is NO, please tell me why and what damage will cause if I design this structure.

3. I saw the block diagram of LTC3779, the IC compare with voltage of Vin and SW1, what purpose is this function work for? What damage will cause if Vin is always bigger than SW1? What situation will happen if this function does not work?

LTC3779 block diagram

Thank you!!

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  • 0
    •  Analog Employees 
    on Apr 24, 2020 9:06 AM in reply to llin786

    Hi 

    For Questions 2 

    it is possible to do so however it would be complex specially if you would target a fully isolated system 

    Mind looking at these controller as alternates ?

    https://www.analog.com/en/products/lt8302.html

    https://www.analog.com/en/products/ltc3803-5.html

    https://www.analog.com/en/products/adp1032.html

    For Questions 3 

    The comparator is used for gate drive functionality of the IC. 

    A bit of which is discussed on page 30 of the data sheet 

  • Hi Mikee :

    Thanks for reply.

    For Question 2,

    I check the link you posted, lt8302 and ltc3803, it looks like use for fly-back control?

    Fly-back is usually use for low power, right? or the transformer may be designed very big.

    For adp1032, I am not sure it is software control or not, but I thought the transformer is the same problem.

    For Question 3,

    The page 30 of datasheet discuss with how the function work, it works to prevent the reverse current from output to input.

    But I am not sure what will happen if this function does not work, and further condition if my Vin is always higher than SW1, what will happen to my circuit, this is what I want to know.

    And I also want to know is this only function that Vin and SW1 use for?

  • 0
    •  Analog Employees 
    on May 19, 2020 8:08 AM in reply to llin786

    Hi 

    For Question 2, 

    Can you discuss more on the reason on why you aim to use adum3224?

    My initial assumption is that you needed an isolated power supply that is why I have suggested Fly back controllers. 

    For Question 3,

    as can be seen on the block diagram the comparator output is input to the buck and boost logic blocks meaning if the conditions are not properly set the controller would not know what logic block should be active at the time and could not properly operate.

    Regards,

  • Hi Mikee : 

    Thanks for reply.

    For Question 2

    I use adum3224 because my specification is input 700Vdc, output 350Vdc. I know it is not the standard usage of LTC3779, but I wanna try if it is possible to use LTC3779 in high voltage situration.

    For Question 3

    I saw the comparator output is connecting to buck and boost logic blocks, so I am just wondering which condition may happen, if lost those information will not make huge damage and just lost some function, maybe I do not need to use those function and I could design LTC3779 circuit without offer those information to LTC3779; or lost those information is very dangerous, LTC3779 may work abnormal and damage my circuit, so I should offer those information to LTC3779 to provide work normal.

    Also, why I need to ask Question 3, because my specification is input 700Vdc, output 350Vdc, and I can not offer SW1, SW2 and Vin signal to LTC3779.

    Thanks for your patient.

    Regards.

  • 0
    •  Analog Employees 
    on Jun 2, 2020 8:52 AM in reply to llin786

    Hi 

    Given the complexity of the modifications need to operate LTC3779 in such conditions. I think it would be best to contact a local ADI FAE to help you on your design. Let them review your requirements and have a discussion with them  

    https://www.analog.com/en/support/technical-support.html

    Regards,