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LM62460: Question about on time

Austin Do
Expert 3275 points
Part Number: LM62460
Other Parts Discussed in Thread: LMR66430, TLVM14406, TLVM23625

Tool/software:

Hello team,

I'm creating the design with the condition, Vin:24V / Vout: 2.3V / Iout :2A.

If I use LM62460, Webench is warning about minimum On time operation. So, if I reduced the switching frequency, the design updated failed due to low phase margin.

webench.ti.com/.../125

However, if I use LMR66430, there is no minimum on-time operation even 2.2MHz switching frequency. On time spec is similar for LM62460 and LMR62460.

So, I'm not understanding why LM62460 cannot satisfy the specification.

webench.ti.com/.../124

Also, if possible, you can suggest the right solution for this condition. The customer is looking for the solution which has high efficient and good thermal performance 

Best Regards,

Austin

  • 0
    TI__Genius 11295 points

    Hi Austin,

    I'll get back to you on this. 

    Thanks,

    Best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    TI__Expert 3275 points

    Hi Taru,

    If possible, the customer also considers using TLVM14406 at the same use case by using single output.

    However, Webench simulation for this device is not available. 

    Can you check this also?

    Best Regards,

    Austin

  • +1 in reply to Austin Do
    TI__Genius 11295 points

    Hi Austin,

    Minimum On Time is a challenge when the duty cycle is very low and switching frequency is high - In your case here - duty cycle is 9.58%. LM62460 will have frequency reduction because of the low conversion ratio. I am not sure if the LM62460 is the best option here since this is a 6A device which is an overkill for a 2A application. Different devices have different internal error amplifiers and their respective compensation network - hence it is possible (in internal compensation devices) to have phase margin limitations even though the off/on time specs are the same. 

    What is the input voltage range? 

    For your application - the best device would probably be https://www.ti.com/product/LMR60420. It is a new device with optimised cost and features. 

    TLVM14406 is a module - with integrated Inductor - so it is also an option to look at if the customer is interested in size optimised power stage designs. It will also offer a simpler and faster time to market. However, it is again, an overkill since this is a dual output design (for 2A/3A) and 4A/6A for single output. Something like: https://www.ti.com/product/TLVM23625 will be the most optimised solution here. 

    I would recommend we discuss this on an internal mail. 

    Thanks,

    Best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    TI__Expert 3275 points

    Hi Taru,

    Thanks for reply. Let me propose TLVM23625. It would be the best fit. 

    Best Regards,

    Austin