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UC2844A: Ambient Temp in Recommended Operating Conditions

Brian Wang0928
Genius 14160 points
Part Number: UC2844A
Other Parts Discussed in Thread: UCC28C44

Customer is confused why there is "no ambient temp range" shown on the Recommended Operating Conditions and also that Junction temp is only specified with -40degee to 105degree? Is there missing info or Typo?

Please help to clarify it. Very thanks. 

Regards

Brian W

  • 0
    TI__Guru 74115 points

    Hi,

    The recommended operating conditions include TA - ambient temperature range - you can look at section 6.3 of the datasheet.

    https://www.ti.com/lit/ds/symlink/uc2844a.pdf?ts=1660705581394&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUC2844A

    Section 6.5 specifies each temperature grade.

    TA = TJ is achieved by minimum power dissipation from the IC and very short test time.

  • 0 in reply to Hong Huang
    TI__Genius 14160 points

    Thanks Hong. 

    Sorry, I made a confusing, the correct device is UCC28C44. 

    How about the recommended ambient temp for UCC28C44? In the datasheet 7.3, it just mentions the TJ, not TA. 

    and which one of below device you suggested?Why? 

    UCC28C44DR

    UC2844AQD8R

    Very Thanks.

  • 0 in reply to Brian Wang0928
    TI__Guru 74115 points

    Hi,

    Then you need to estimate power losses based on your MOSFET, fsw and IC bias current, VCC/VDD, then using thermal resistance to estimate what TA can be ok in your design/application.

    Any of these devices are ok. You may need to make your mind to create specs for your design then to check which one is better. If all are good, then maybe consider cost as another factor for our decision.

  • 0 in reply to Hong Huang
    TI__Genius 14160 points

    Why d/s didn't specify the suggested Ambient temp? Could you offer the example on how to calculate this P_loss and estimating the thermal rising. thanks. 

    Regards

    Brian

  • 0 in reply to Brian Wang0928
    TI__Guru 74115 points

    Hi,

    It is one way to specify with Tj. A designer can estimate power losses from the MOSFET and fsw to find what TA can be. So Tj is a more general way while TA can be specified / recommended based on worst power losses.

    Basically, you need to find your MOSFET, fsw, VCC/VDD, to estimate your driving power needed. You can search the web to get how to estimate the MOSFET driving power and get references easily. Usually you need to add margin with the worst case. The IC has about 2mA bias power in the case of UCC28C44. So 2mA x VDD is IC bias power and plus the MOSFET driving power + margin - that is an estimation of P_loss then using this to calculate Tj to make Tj not exceeding specs after adding your TA.