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WEBENCH® Tools/LM5155: WEBENCH design not created

Ue
Genius 17445 points

Part Number: LM5155
Other Parts Discussed in Thread: LM3478

Tool/software: WEBENCH® Design Tools

Hi all 

While trying to create a WEBENCH design with the LM5155 with these (... or similar ...) parameters:

Vin=5V ... 6V

Vout=50V, Iout=1A I get below error message.

Can you look into this ?

Best regards

Ueli

----------------------------------------

Design cannot be created!

Your preferred device does not work with the inputs you selected.

Please change your inputs or select another device.

  • 0
    TI__Expert 5920 points
    Hi Ueli,

    We are able to replicate the issue. Currently analyzing to verify if its a valid fail.
    Shall keep you updated on the fix.

    Thanks and Regards,
    Umayal
  • 0 in reply to Umayal Ramanathan
    TI__Expert 5920 points

    Hi Ueli,

    Its a valid fail. As per Boost duty cycle equation Dboost=1-(vin/Vout), for reported condition duty cycle is 90%.

    As per datasheet considering worst case ,duty cycle is 80% as shown in image below. For the reported condition duty cycle exceeds maximum duty cycle.

    Thanks and Regards,

    Umayal

  • 0 in reply to Umayal Ramanathan
    TI__Genius 17445 points
    Hi Umayal

    Thank you for the quick reply and understood, my oversight, I didn't checkt the max duty-cycle for the LM5155.

    For the above specification the LM3478 (Datasheet specifies 100% max duty-cycle) could be used and WEBENCH does generate such a design.

    Best regards

    Ueli
  • 0 in reply to Ue
    TI__Intellectual 2320 points
    Hi Ueli,

    We were able to create design for 5V-6V to 50.00V @ Iout = 1A for LM3478. Kindly let us know if you are facing any issue creating the design.

    Thanks & Regards,
    Harish
  • 0 in reply to Harish K R
    TI__Genius 17445 points
    Hi Harish

    Thank you for the feedback. I picked the above specs as placeholders for a wide Vout/Vin design.

    What my customer is looking for is a boost 5V => 150V / 0.03A and this seems challenging.
    Webench doesn't generate a design for these specs with the LM3478 either.
    Going for these parameters: 5V ... 6V => 120V / 0.03A with the LM3478 Webench provides below warning, not sure what this should indicate.

    Best regards

    Ueli
    ----------------------------

    With the design conditions, either the IC or the selected FET junction temperature is exceeded above the maximum rating. Hence, this design is created using an ideal FET. Please note that the resulting FET parameters are ideal, so the efficiency/loss opvals have been disabled. Also, the schematic/PCB export and Thermal simulations will not work with the ideal FET.
  • 0 in reply to Ue
    TI__Intellectual 2320 points

    Hi Ueli,

    Below are the recommendation from WEBENCH for 5V- 6V => 150V / 0.03A.

    Kindly note that LM2585-ADJ and LM2587-ADJ recommended (as per above image) are flyback designs.

    You can follow steps highlighted in below image to find out designs recommended by WEBENCH for any conditions

    Regarding your query on below WEBENCH Alert message: It only means that WEBENCH wasn't able to find practical FET that can support the desired power requirement and hence has used ideal FET to create design. In such cases, we cannot estimate FET power losses and hence the device efficiency.

    This is because the number of FETs in our WEBENCH database is limited but practically we might be able to find FET that can support desired power requirement, VDS rating etc.

    "With the design conditions, either the IC or the selected FET junction temperature is exceeded above the maximum rating. Hence, this design is created using an ideal FET. Please note that the resulting FET parameters are ideal, so the efficiency/loss opvals have been disabled. Also, the schematic/PCB export and Thermal simulations will not work with the ideal FET."

    Kindly let us know if you have any queries.

    Thanks & Regards,

    Harish

  • 0 in reply to Harish K R
    TI__Genius 17445 points

    Harish

    Understood and thank you for the reply.

    As discussed it seems that Webench has currently some limitations as fas as supporting high duty-cycle boost designs are concerned.

    Best regards

    Ueli