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TPS54362-HT getting hot

Other Parts Discussed in Thread: TPS54362-HT

Hi,

We are using TPS54362-HT in a following DCDC application:

Ambient temperature max: 175 deg C

Input to TPS54362-HT: 18V

Output from TPS54362-HT: 5.5V  

And furter converted to 1.8V, 5.5V and 3.3V.

While testing prototypes of the boards we noticed that the surface of the TPS54362-HT chip is warmer than ambient temparature: 

At 30 deg ambient - 60 deg on the chip

At 175 deg ambient  - 203 deg on the chip.

Measured with a thermocouple taped to the surface of the chip.

Is that normal for the package temp to be ca 17 deg over ambient??

We ran the board for a good hour in 175 deg but apart from the high temperature on the chip we did not notice any degradation in performance. We'll do some more testing (24 h and 200 h).

Regards,

Aleksander

 

 

  • It is absolutely normal for the IC case and junction temperature to exceed the ambient temperature.  The only time the junction and ambient temperatures would be equal is when there is no power dissipation in the IC (no power at all supplied to your board).  The junction to ambient temperature difference may be as high as 37.5 C/W (see datasheet page 4).  That number is for a JEDEC standard board.  A well designed PCB may have substantially better performance.  If youa re accurately measuring the top case temperature, then the junction temperature will be 0.5 C/W above the measured case temp.  A taped on thermal couple is not a very accurate method though.  We use a thermal imaging camera to get accurate results.  Can you tell us your power dissipation for the TPS54362-HT?  Also you can look here for more info on thermal parameters;

    http://www.ti.com/lit/an/spra953b/spra953b.pdf

  • Hi John,

    Thank you for quick answer. 

    Power dissipation is ca 2.5 W.

    We have an IR camera and will use it to maesure the IC temperature during next week testing.

    Regards,

    Aleksander