LTM8055 Parallel Operation

Hello,

I have a few questions about the LTM8055.  The LTSPICE demo circuit for parallel LTM8055  found here https://www.analog.com/en/products/ltm8055.html#product-tools shows a large voltage overshoot on startup and very high current demands from the modules.  Is this realistic of the modules in a parallel configuration or is this a simulation artifact?  The datasheet doesn't mention anything about parallel startup being a problem.   The single device LTSPICE model doesn't have this problem.  The simulation is for a 12V output and the voltage goes to almost 24V before settling.

Unrelated to the simulation, does the device have short circuit protection in all modes of operation (buck and boost)?  Do I need to do anything special for parallel devices for fault protection?  Do they have any circulating problems during faults?

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  • 0
    •  Analog Employees 
    on Sep 11, 2019 8:40 AM over 1 year ago
    • Hi, I also see an overshoot in my simulation, I suspect that this is due to imperfection of the LTSpice model. Let me verify this in bench and I'll get back to you as soon I get the result. 
    • As for your other questions, it is stated in page 9 of the data sheet that "an output sense resistor is required to adequately protect the LTM8055/LTM8055-1 against output overload or short-circuit". This is applicable in all modes of operation of the LTM8055.
    • Kindly refer to page 11 of the datasheet if you are going to use this in parallel operation. Additional fault protection may be required as stated in page 14 when the input voltage rises above a predetermined threshold due to some applications where the FB pin is abruptly driven to a new voltage.

    Regards, 

    Fritz

  • Hi Fritz,

    Did you get a chance to look into the parallel overshoot?  Is it just a simulation issue?  I've noticed that the LTspice model is different than the parallel model on page 20 of the datasheet.  The datasheet shows a capacitor on the compensation pin.  I modified the LTspice model to match the datasheet but still the same problem.  Also, I don't see where the datasheet explains the compensation for the control.

  • Hi , 

    I have the same problem but with LTM8056.

    If you have an update please let me know. We are planning to place a Load Switch if it really occurs on the board .

    Thanking you 

    With best regards and wishes 

Reply Children
  • 0
    •  Analog Employees 
    on Dec 18, 2019 1:34 AM over 1 year ago in reply to kabekami

    Hi, we are looking into this and will get back to you after the holidays. 

    Regards,

  • +1
    •  Analog Employees 
    on Jan 20, 2020 1:50 AM 11 months ago in reply to FCGonzales

    Hi, here's the result of the startup test of LTM8055 in parallel configuration with 24V input (Blue), 12V output (pink), and 12A load (green). The result shows unnoticeable overshoot in the output voltage. 

    Take note that I have used two DC2017A evaluation board for this test. One working as a master and the other one working as a slave. Make sure to make the connections of Imon, CTL, SYNC, CLKOUT, and GND as close as possible to avoid noise interference in the circuit. There is also a provision for LT1636 isolator in the evaluation board of LTM8055, so you don't have to make another board for it. 

    Regards.