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LME49600: Junction to case thermal resistance

Part Number: LME49600
Other Parts Discussed in Thread: BUF634


We are replacing BUF634 with LME49600 in one of our designs.

In the thermal information of BUF634 junction to case thermal resistance is mentioned separately for top and bottom.

But in case of LME49600, it is not mentioned separately. Only junction to case thermal resistance is given.

Do you have this information separately for LME49600? We need it for a few calculations.

If you have the data, please share it.


Aneesha CM

Hardware Engineer,

GE India, Hyderabad.

Ph: 6238415457

  • Hello Aneesha,

    Junction-to-Case thermal resistance values correspond to the quantity RθJas discussed in whole of Section 2: RθJC Junction-to-Case in the TI Semiconductor and IC Package Thermal Metrics document.  While most TI parts include a single RθJC value , product lines & IC designers can add θJC as two separate values when necessary.  The value for RθJC(top) or RθJC(bot) corresponds to mechanisms for removing heat present at either the top or bottom of the package.  The BUF634 has a mechanism at the top of the IC & the option (depending on package selection) of a thermal mechanism at the bottom.  When the bottom mechanism is relevant & present; the RθJC(top) value is provided.

    For the LME49600, there is only a single Junction-to-Case thermal mechanism: the IC's KTT package is completely different from the BUF634's DDA, DRB, or SOIC packages.  The BUF634's SOIC package has no RθJC(bot) value because there is not a relevant value to share: this is the same as the LME49600.  When only a single Junction-to-Case thermal mechanism is present, the singular RθJC properly specifies the thermal interaction.

    I encourage a read of the Semiconductor and IC Package Thermal Metrics paper (specifically Section 2 for your question), as it enables clarity over an often misinterpreted subset of IC specifications.

    Also, there is an upgraded version of the BUF634 now available: the BUF634A