Author Topic: BD9870FPS Buck switcher: Thermal resistance not stated --> no heatsink needed?  (Read 2135 times)

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Offline 741Topic starter

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I'm looking for an IC to step dowm from 24V to 5V, 150mA.

The ROHM BD9870FPS http://rohmfs.rohm.com/en/products/databook/datasheet/ic/power/switching_regulator/bd9870fps-e.pdf has no mention of "thermal resistance". All I can find is "Power Dissipation" = 0.8W. (Some ambient temperature derating is given).

Does that mean that its Rja (junction to air thermal resistance) is low enough that the device can simply be mounted on normal sized pads? That would be good news as it means prototying is easier.

Even so, it might not be appropriate as it becomes very inefficient under about 200mA output.
« Last Edit: December 16, 2019, 03:36:39 pm by 741 »
 

Offline T3sl4co1l

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I've got a LMR14203 here, that doesn't seem to care, i.e. it doesn't get hot at similar loads.

5V 200mA is only 1W total output, how inefficient were you expecting it to be?

Bigger pads and inner layers are always welcome, thermally speaking.  Leave thermal spokes in for solderability.

Tim
Seven Transistor Labs, LLC
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Offline 741Topic starter

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Thank you, having an actual tried-out part number is ideal. I had a figure of 85% efficiency in mind. The curve for the 9870 is attached. I should have looked at lower power parts.


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