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  • Do Ψjt, θja, and power dissipation vary by the size of the board? How can I predict the power dissipation, the Ψjt, and the θja of the board we have designed?
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Question

Do Ψjt, θja, and power dissipation vary by the size of the board? How can I predict the power dissipation, the Ψjt, and the θja of the board we have designed?

Answer

LDO Linear RegulatorsPackage

Power dissipation and thermal resistance are affected not only by the size of the board but also by the number of layers, the thickness of the board, the wiring width and length, layout, etc.

When the wiring width and length, and layout pattern of whole parts are equal, the larger the board, the lower the thermal resistance.

The θja and the ψjt can be calculated by the formula below.

θja=Tj-Ta/Pd, ψjt=Tj-Tt/Pd

The actual θja and the ψjt depend on your board and mounting conditions, and may differ from the θja and the ψjt in the datasheet.

If you want to know the thermal resistance of your board with Ricoh devices, we may be able to help you by thermal simulation if you let us know the board information. Please feel free to contact us.

Definition of θja and ψjt

Definition of θja and ψjt

θja : Thermal resistance between junction temperature (Tj) and ambient temperature (Ta)

ψjt : Thermal resistance between junction temperature (Tj) and package mark surface center temperature (Tt)

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