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SN6501-MULXFMR-EVM temperature dependance of efficiency

Other Parts Discussed in Thread: SN6501-MULXFMR-EVM, SN6501

Dear all,

Our customer is studying SN6501-MULXFMR-EVM now.
I have gotten a question regarding SN6501-MULXFMR-EVM from the customer.
So please teach me about it.

[Question]
How much is temperature dependance of conversion efficiency regarding part of isolated power supply?
Input current increase about 1.5 times when ambient temperature changes from 25℃ to 105℃ though load current is fixed.

Best regards,
M. Tachibana

  • Hello Masanori,

    Temperature dependance of the device is tested for all the electrical and switching characteristics listed in the datasheet and Efficiency (which is a system level parameter) is not tested across temperature.

    By looking at these parameters, one of the parameter that changes efficiency is rDS(ON) of push-pull MOSFETs internal to the device. Under worst case conditions the ON resistance changes from 1Ω typical to 3Ω max causing losses to increase three folds. Assuming efficiency at 25C to be 85%, the loss is 15%. At 125C, the worst case loss due to temperature increase should be 3*15% = 45% and hence estimated efficiency should be at 55%.

    Hence,
    at 25C, n = 85%,
    at 125C, n = 55%

    Assuming input and output voltages are same and considering an input current of 100mA at 25C, output current should 85mA due to an efficiency of 85%. At 125C with an efficiency of 55%, to maintain the same output current of 85mA I would need to input 154mA of input current. Thus an increase in input current by ~50%.

    Regards,
    Koteshwar Rao
  • Dear Koteshwar-san,

    Thanks for prompt reply to my question.
    I understood temperature dependence of SN6501 output.

    Our customer wants to know the temperature dependence of SN6501-MULXFMR-EVM total.
    He is evaluating 5V: 5V No LDO and 5V:5V LDO portions of EVM.
    Each load current is set to 10 mA.

    In this case, when temperature changes from 25C to 105C, each input current is as follows.

    5V: 5V No LDO : 24mA -> 36mA
    5V:5V LDO :  28mA -> 46mA

    Are these would be a reasonable value?
    Is there any data of such a temperature dependence regarding SN6501-MULXFMR-EVM?

    SN6501, transformer and Schottky barrier diode which are components of EVM have possiblity for temperature dependent.
    Which device is  significant influence for temperature dependence?

    Best regards,
    M. Tachibana

  • Hello Masanori-san,

    I understand your customer's requirement. Considering there are many temperature dependent components on the EVM, I would expect the values mentioned by you to be normal. We characterize the device SN6501 as part of device development hence we wouldn't have similar temperature dependent data for other components on EVM. You may find such information from respective vendors and their datasheets.

    All three components you have mentioned (SN6501, transformer and Schottky barrier diode) should have similar temperature dependence.

    Regards,
    Koteshwar Rao
  • Dear Koteshwar-san,

    Thanks for your reply.
    I can get the information of approximate temperature dependence of transformer and Schottky barrier diode from the website of the manufacturer that made them.
    So I can know the characteristics of individual components.
    And I understood that no data of temperature dependence regarding SN6501-MULXFMR-EVM.
    If I know total temperature characteristic of SN6501-MULXFMR-EVM, I must estimate it using each data of those components.
    Isn't it so?

    Best regards,
    M. Tachibana
  • Masanori-san,

    Yes, your understanding is correct.

    Regards,
    Koteshwar Rao