• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 47 subscribers
  • Views 111 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA547: OPA547FKTWT Thermal Resistance Values

John Blasko
Prodigy 30 points
Part Number: OPA547
Other Parts Discussed in Thread: LMH6321

Tool/software:

Hello,

Could you provide/confirm the thermal resistance values for OPA547FKTWT.

1) Theta Jb (Bottom) (I believe this is 3 per the datasheet)

2)Theta Jc (Top)

  • 0
    TI__Genius 14616 points

    Hey John, 

    1. Theta JC(BOT) is 3C/W at DC. Theta JB would depend on your PCB design. 

    2. Due to the age of this device, and this being a surface mount thermal tab, we did not separate theta JC(BOT) form theta JC (top).  Furthermore, on a package like this, it is assumed that a significant amount of heat will be transferred through the heat slug rather than the case top.

    I think the best plot to use is as below:  

    Figure 4 will allow you to easily calculate junction temperature of the device relative to copper area, power dissipation, and ambient temperature. 

    Here is a nice article covering how we characterize thermal performance for devices like this: How to Evaluate Junction Temperature Properly with Thermal Metrics

    Please let me know if you have any questions here. 

    Thanks,

    Jacob

  • 0 in reply to Jacob Nogaj
    Prodigy 30 points

    Hey Jacob,

    Thanks for your response, understood the bottom of the package will be the primary heat path for this device. For my application, it is necessary to top cool even though it would not be a primary heat path in order to distribute some of heat. I found the following PN:LMH6321 | Buy TI Parts | TI.com which also has the DDPAK 7 pin KTW package that has the Jc Top characteristics determined. Would it be reasonable to assume that the Jc Top shown in this datasheet is similar to what the Jc of OPA547FKTWT might be? or are there design factors internally that would make this a bad comparison.

  • 0 in reply to John Blasko
    TI__Genius 14616 points

    Hey John,

    Good to know, I see how the theta JC top is important to know here. 

    Sometimes these thermal metrics can change as much as +-20% in my experience within the same package. LMH6321 is a good cross part to the OPA547. Generally, I want to see that the device is a somewhat similar power level to the comparison device. 

    I think as a ballpark estimate we can consider 34.4C/W to be the theta JC top for OPA547 in KTW package. 

    Thanks!

    Best,

    Jacob

  • 0 in reply to Jacob Nogaj
    Prodigy 30 points

    Awesome, good to know and have a rough idea on how much that JC top can change. Appreciate you looking into this sim-to package and providing your opinion. This should help me keep moving forward in my design. Thanks!