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TPS61085 operating temperature

Chris Knox
Prodigy 10 points
Other Parts Discussed in Thread: TPS61085, TPS61087

Hello folks.

I'm using a TPS61085 boost converter to power some 12 volt fans from a 3.3 volt supply. The fans draw a total of 0.34A at 12 volts. The question I have is how hot should the converter be? With an ambient temperature of 24 degC, its case has reached 64 degC. I have a goal of operating this supply up to 55 degC ambient, and I'm worried that this will be too hot for the converter. I've also measured the inductor and diode temperatures, which are 38 and 32 degC respectively.

The power supply design is nearly identical to that described in figure 12 of the TPS61085 datasheet (here: http://focus.ti.com/lit/ds/slvs859/slvs859.pdf ), although I have substituted to use in-house components where possible.

Is it possible to dissipate some of the heat out of the converter's leads into a copper plane or tracking, and if so which of the leads would be best?

As an aside, I've implemented speed control by using MOSFETs switch in different resistors between the feedback pin and ground. It works quite well, and appears to be an effective way of controlling the fan speed.

 

Best Regards,

Chris

  • 0
    TI__Guru 65340 points

    Hello Chris,

    First of all, it is not possible to destroy the part by overlaod. The part has an overtemperature protection which will stop switching if it gets too hot. If this happens, the converter will start again when its temperature reduced by typically 14°C. Your application will have an increased output voltage ripple and maybe a reduced output voltage, but the converter will still be functional.

    If you have the possibility to increase the ambient temperature somehow, you will be able to observe this behaviour.

    The heat inside the converter is almost exclusively generated in the switch and therefore for better thermal performance copper at pins SW and GND could help, but we did not test more copper than used on the Evaluation Module. (Maybe you can use the fans you power with the part to cool the part?)

    If you want to use a part with a better thermal performance, you could use TPS61087 which has higher output current and is in a QFN package with a thermal pad on the bottom. Here the power can be dissipated by the GND plane the thermal pad is soldered to.

    Best regards,
    Brigitte