This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

WEBENCH® Tools/LM5122EVM-2PH: Design dual phase Lm5122

Part Number: LM5122EVM-2PH
Other Parts Discussed in Thread: LM5122, TINA-TI

Tool/software: WEBENCH® Design Tools

Dear Forum-reader,

We try with the LM5122 in Dual-phase design ( Design = originally from the TI - site ) to convert an Input voltage (3 - 4,5Vdc / 50Amp) to an Output voltage of 24Vdc.

We changed R21 (for setting the UVLO-Pin of LM5122 for lower input voltage). (We used the formulas in the LM5122 pdf document)

Input Voltage:4,5V is minimum start-up voltage ... and we want it to work to as low as 3V (or 3,5 - 4V)  if possible with a continuous amount of current (max 50A continuously).

The output voltage is already set to 24Vdc. (with R26, R27, R28).

We changed the filter between the Comp- and FB-Pin (R25, C25, C26).  (We used the formulas in the LM5122 pdf document)

We changed the Input source to a battery (settings: 4,5V and tried it also with 5V)

WE USED   =NOT=  Webench simulation tool  =  BUT : TINA-TI Simulation tool for the schematic below. 

 

Questions: 

1) Is it possible to change the simulation speed ? (it takes about 1 to 2 hours)

2)  If we look at the simulation values, the Vout is not reaching 24Volts.

=> Is there something we do wrong ?

3) If we look at the simulation values, the LO and LO_S Fet switching gate signals stop before the 1ms... strange.

=> How and why does this happen ?  

Who can help us out with these questions ?

Thank you for your time,

Anthony and Heba.

  • Hi Heba,

    Thank you for considering the LM5122 in your applications.  You may order our LM5122 dual phase EVM for an evaluation. 

    Simulation in TINA or pspice can take a fair amount of time for dual phase circuit owing to the large number of circuit nodes. Anyway, you should be run the simulation.

    From your description, I am afraid you hit the peak current limit:  you have a very large output capacitor and your soft start time is short, and at the same your load is always attached.  I would first simulate with a smaller load, and also with longer soft start timer (SS capacitor need to be increased).  Once you get the stable output voltage, you may add the load. 

    When the circuit high the peak current limit, it will cut down the duty cycle, hence you will not be able to establish the required output voltage. 

    Thanks,

    Youhao Xi, Applications Engineering

  • Hi,

    Thanks for your reply, I already tried to make the load less but the out put voltage does not reach 24volt. I tried to see the datasheet but I cannot see any clear information how to set up the values of the components when I am using dual phase.

    If you can give me an tips or something then please let me know.

    Regards Heba,

  • Hi Heba,

    For dual phase, you simply design for the single phase, for 50% power, then duplicate the design for the other phase, and modify the clock daisy chain connection and also the Feedback control.   Can you try to reduce your current sense resistor?

    Thanks,

    Youhao

  • Hi,

    I already try to reduce the current resistor sense but it doesn't work.

  • Hi Heba,

    The schematic that you attached looks like the TINA schematic for the simulation. Can you attached your model so we can take a look?  

    Thanks,

    Youhao

  • 4341.dualphase(heba)v 6.TSC

    hi, this is the schematic. i hope that you can help me.
    New mailCopy
  • Hi Beba,

    We will investigate this, and we will get back to you by next Wed.

    Thanks,

    Youhao

  • Hi Heba,

    Please see the simulation result below. The issue was the hiccup caused by over current at startup. I only changed the Rsense to 1mohm and Css to 80nF.

    Please let me know if you have any questions.

    Thanks,

    Yinsong

  • Hi,

    Thanks for your reply, I will try it and then i will let you know.

    Regards Heba,

  • Thank you Yinsong,

    Hi Heba,

    Please let us know if you still see issues. 

    Best Regards,

    Youhao

  • hi,
    i simulate it, but i am not getting the same curve. which one did you used. i changed the current sense resistor to 1mohm and also css to 80nf. can you send your file. 
    did you change any thing else.
    i have small question: if I want to change the vin to 3 v and the output voltage is 24 volt , it will be easy or do I have to change any thing in the components.
    regards heba,
    New mailCopy
    What do you want to do ?
    New mailCopy
    What do you want to do ?
    New mailCopy
  • What do you want to do ?
    New mailCopy
    hi, 
    it is work now. thanks for your help.
    i have two small question:
    1-if i changed the vin to 3v, and i want to make the vout 24v do i have to change anything .
    2- what is the different between the initial zero and the operating point and initial condition.
  • Hi Heba,

    1. Minimum VIN operating voltage is always 4.5 V. The minimum input power supply voltage can be 3 V after start-up, assuming VIN voltage is supplied from an available external source.

    2. the first option lets TINA calculate the DC operating point based on the initial conditions set before the time domain iterations. If you want to skip this, then choose initial zero, which sets all initial condition to zero, or use initial conditions, which sets all initial conditions to zero except the ones set on the schematic.

    Please let me know if you have any questions.

    Thanks,

    Yinsong

  • thanks for your explanation. i will work on it . it is now clear. if i have question later then i will ask later or open another question. i dont have at this moment to ask . thanks for your help
    New mailCopy