I am not very knowledgeable, so please bear with me.

For heat sink calculation, you need the junction-to-case thermal resistance of the chip, then the case-to-ambient thermal resistance of the heat sink. Why are there datasheets that don't contain the junction-to-case thermal resistance? One example is this LTC1732-8.4:

package image with thermal values from LTC1732-8.4 datasheet

How can you do heat sink calculation without the junction-to-case thermal resistance? Since only the junction-to-ambient resistance is provided, does that mean this chip package doesn't support a heat sink?

The formula I know for heat sink calculation is:


where \$T_j\$ is the junction temperature, \$T_a\$ is the ambient temperature, \$\theta_{JC}\$ is the junction-to-case resistance of the chip, and \$\theta_{CA}\$ is the heat sink case-to-ambient resistance.

  • 3
    \$\begingroup\$ Is this a specific or general question? LTC1832 draws a couple mA, you'd be hard pressed to get it self-heated any at all. \$\endgroup\$ Dec 10, 2022 at 22:13
  • 1
    \$\begingroup\$ Yeah, "Input Supply Current: 3 mA" maximum. \$\endgroup\$
    – pipe
    Dec 10, 2022 at 22:33
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    \$\begingroup\$ packages without exterior exposed metal surfaces aren't designed to take heatsinks, usually out of a lack of need or an internal bottleneck that runs out of margin long before case temp is problematic. Sometimes tacking on a heatsink can result in somewhat better operation (chip amps, RAM, LEDs, motor controllers, PIs, etc) but these are more subjective improvements than design requirements with engineering specs. \$\endgroup\$
    – dandavis
    Dec 10, 2022 at 23:42
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    \$\begingroup\$ @dandavis so, is it safe to assume then that if not \$\theta_{JC}\$ is provided, then the chip is not meant to be used with a heat sink? \$\endgroup\$
    – Schach21
    Dec 11, 2022 at 0:27
  • 1
    \$\begingroup\$ As pipe says, input current is 3mA maximum, so why do you think it needs a heatsink? \$\endgroup\$ Dec 11, 2022 at 3:12


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