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LM5022-Q1: LM5022-Q1 operating frequency restriction at webench

Kanthavel Kumaran
Prodigy 100 points
Part Number: LM5022-Q1
Other Parts Discussed in Thread: LM5022

Hello TI team,

 

Kindly find my design requirements and queries as follows:

 

Design requirements:

 

VIN: 6V to 16V

Vout: 45V

Output current: 0.5A

Operating temperature max: 95

 

Queries:

While providing the above inputs at webench, it restricts the operating frequency range with 200KHZ. But as per datasheet LM5022 can be able to operate up to 2MHZ. Hence please explain why frequency restriction is there in the webench. If I need to increase the frequency range in the tool, what need to do?. Please provide your feedback
While simulating the above inputs at Webench, it provides 10A rated diode part number. And calculated I peak value is 4.4A. I want to check to go with lower current rating diode part. So please suggest lower current rated diode part if possible.
 

Thanks,

Kanthavel Kumaran

  • 0
    TI__Mastermind 31315 points

    HI Kanthavel,

    Thank you for using the LM5022 in your design. Here are my responses to your questions:

    1) Frequency restriction can be due to a few things. 

    • Thermal concerns, since higher switching frequency is associated with higher power loss. At such a high operating temperature (95C ambient), there is a possibility that you may damage your MOSFET.
    • Modeling data, since Webench models are based off of live data, it is possible that the model does not include data taken at high switching frequencies at high ambient temperature. That being said, the LM5022 will be able to hit the specifications marked in the datasheet.
    • maximum duty cycle / Minimum off-time is spec'd at ~500kHz in the datasheet, but in your application, you are operating close to maximum duty cycle limit of 90%. It is possible at higher switching frequencies, you will run into minimum off-time, so a lower frequency is also used.

    Unfortunately, given your current operating conditions, the tool does not allow for modification of frequency range. If you would like to do so, you will need to test on the bench.

    2) I would advise against going to a lower current rated diode part, since you would like to have some margin to prevent damage via over current/over temperature, especially at high ambient temperatures. I think looking at a thermal response chart would be very helpful in selecting a component, because you would want to not exceed the diode's maximum operating temperature.  

    Thanks,

    Richard