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WEBENCH® Tools/TPS61087: Ask for help about WEBENCH stimulation with two error message

Jie Tian
Prodigy 10 points
Part Number: TPS61087
Other Parts Discussed in Thread: TINA-TI, TPS61088, TPS55340, TPS55330

Tool/software: WEBENCH® Design Tools

Customer use TPS61087(Step-Up DC-DC Converter) for simulation, input voltage is 5V ,output voltage is 12V. From the datasheet we can see maximum output current is about 1.3A .   

However,  if we set output current 1.1A and change inductor and diode value(to meet the requirement of output current), WEBENCH didn’t work. The error message is shown as fellows.

The schematic for simulation is shown as fellows.

So the problem is why WEBENCH failed in this condition. Customer wants to know if output current is a little larger than 1A, what should we do?

  • 0
    TI__Intellectual 1045 points

    Hi Jie,

    We are looking into this. Will get back you soon.

    Best Regards,

    Mahantesh

  • 0
    TI__Intellectual 1490 points

    Jie Tian,

    WEBENCH is failing the design because the calculated value of the switch current exceeds the switch current limit of 3.2A. This assumes an Inductor current ripple of 30% and ~85% efficiency.

    With smaller Inductor current ripple (using larger Inductor) and higher efficiency (small DCR, low Forward drop diode etc)  - the part can support up to  maximum of 1.3A output current at your design condition as given in the datasheet. I suggest two options:

    1) Create WEBENCH desing at 1A load and modify it in your favorite CAD tool to support 1.1A current:

    You may create WEBENCH design at 1A and export the design to supported CAD tool (TINA-TI / Altium/OrCAD) and you can use this as starting point for your 1.1A design - increase Inductor value, chose a diode with smaller drop and you can try to simulate for 1.1A load and make sure that your switch current does not exceed 3.2A. Attached design may work for your needs.

    TPS61087_1.1A_load.tsc

    2) Please consider using alternate parts suggested by WEBENCH which will work best for your design conditions (For example: TPS55330, TPS55340, TPS61088 etc) .

    Regards,

    Srikanth Pam | Online Design Tools

  • 0 in reply to Srikanth Pam
    TI__Mastermind 21795 points

    Jie Tian,

    Also, to add to what Srikanth said, the datasheet figure is probably based on a more typical value of switch current limit which is 4A in this case. WEBENCH is more conservative and uses the minimum switch current limit of 3.2A from the electrical characteristics of the datasheet. Hope that helps explain the possible discrepancy as to why the design creation fails. Internally, the design algorithm tried to reduce the ripple current as much as possible by using the max inductor of 6uH for the 1.2MHz frequency (details given on page 11 in inductor selection section). But inspite of that, the peak current ends up being greater than the 3.2A limit. 

    Please let me know if you have any more questions.

    Regards,

    Amod