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WEBENCH® Tools/LM5122: Alert Message in the Simulation of LM5122

Danilo A.
Mastermind 28920 points
Part Number: LM5122

Tool/software: WEBENCH® Design Tools

Hi Team,

When the customer simulated LM5122 in Webench Power Designer with the specifications below, the simulation run without error or warning. But when he clicked the "Customize" button and changed the Vin from 7-15V to 12V, an alert message about the MOSFET M1 junction temperature appeared. Please refer to the Webench schematic diagram and screenshot of the alert message below. 

Specifications:

VinMin = 7V

VinMax = 15V

Vout = 50V

Iout = 5A

Webench schematic diagram

https://webench.ti.com/power-designer/switching-regulator/customize/48

Upon checking the alert message he found that the junction temperature of the IPB027N10N3G MOSFET is 182.38°C, which exceeds the operating temperature of 175°C as defined in the datasheet.

However, the software informs him that “All above values ​​are estimates. For more accurate values, please run electrical simulation ”. By doing the simulation at the same operating voltage (Vin = 12V), everything seems correct and the junction temperature of the IPB027N10N3G MOSFET mentioned in the report is 162.61°C, which is lower than the maximum value in the datasheet .

His concerns are as follows

1. Why is there an alert message when everything seems correct according to the results of the simulation?

2. Why is there an alert message when Vin = 12V, but no alert for VinMin and VinMax are 7V and 15V respectively?

Regards,

Danilo

  • 0
    TI__Expert 8365 points

    Hi Danilo,

    The quantity of M1 fet is 2 , the current through fets divides and Junction temperature decreases. We will check why this alert message is being displayed. We will get back to you.

    Thanks & Regards,
    Praveen

  • 0 in reply to Praveen Badiger
    TI__Expert 3320 points

    Hi Danilo,

    Apologies for delay here. After careful debugging we found out that this is a bug with Webench model for LM5122. For your input case Webench should not have selected the actual mosfet. Rather it should have selected Ideal Fets (due to limited fet database and failure to stay inside junction temperature limit). 

    To answer specific queries, while selecting fets for a design, we do consider if Fets are working fine on VinMin, VinMax and extreme cases. Due to bug, these fets were getting selected but failing for in between input (Vin). Hence the alerts. We have corrected the model and should be available on ti.com by mid of next week. Hope this helps. Let us know if you have any more queries.   

    Best Regards,

    Bhushan

  • 0 in reply to Bhushan Waghmare
    TI__Mastermind 28920 points

    Hi Bushan,

    Thank for your effort in finding the cause of this issue. I will update the customer that the issue has been fixed and will ask him to retry the simulation by mid or late next to see if the online simulation is working according to the fixed you have implemented in the model. 

    Thank you very much for your time and effort fixing this issue.

    Regards,

    Danilo

     

  • 0 in reply to Danilo A.
    TI__Expert 3320 points

    Sure Danilo,

    We will let you know once the updated model is available on ti.com for testing (probably by end of next week).

    Best Regards,

    Bhushan  

  • 0 in reply to Bhushan Waghmare
    TI__Expert 3320 points

    Hi Danilo,

    Updated model is now available on ti.com. 

    Best Regards,

    Bhushan  

  • 0 in reply to Bhushan Waghmare
    TI__Mastermind 28920 points

    Hi Bushan,

    Thank you for the update. We have tried simulating LM5122 in Webench after the update but another message alert appeared. Please see the message alert below. It seems the bug in the model has not been fixed.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Expert 3320 points

    Hi Danilo,

    There was a bug in model, Webench was giving the actual mosfets solutions even if these were hitting junction temperature for your input case. After fixing the bug, Webench is selecting the ideal fet solution (not actual Mosfet solution) due to limited fet database and other fets's failure to stay inside junction temperature limit (please see my first reply). As Webench is not able to find actual Mosfet solution, the alert for ideal fet is displayed. Hope this helps. Please let us know if you have any more queries.

    Best Regards,

    Bhushan