8P34S2108NLGI datasheet(15/20 Pages) IDT

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October 20, 2016

8P34S2108 Datasheet

Case Temperature Considerations

This device supports applications in a natural convection environment which does not have any thermal conductivity through ambient air.

The printed circuit board (PCB) is typically in a sealed enclosure without any natural or forced air flow and is kept at or below a specific

temperature. The device package design incorporates an exposed pad (ePad) with enhanced thermal parameters which is soldered to

the PCB where most of the heat escapes from the bottom exposed pad. For this type of application, it is recommended to use the

junction-to-board thermal characterization parameter JB (Psi-JB) to calculate the junction temperature (TJ) and ensure it does not

exceed the maximum allowed junction temperature in the Absolute Maximum Rating table.

The junction-to-board thermal characterization parameter, JB, is calculated using the following equation:

TJ = TCB + JB x PD, where

TJ = Junction temperature at steady state condition in (oC).

TCB = Case temperature (Bottom) at steady state condition in (oC).

JB = Thermal characterization parameter to report the difference between junction temperature and the temperature of the board

measured at the top surface of the board.

PD = power dissipation (W) in desired operating configuration.

The ePad provides a low thermal resistance path for heat transfer to the PCB and represents the key pathway to transfer heat away from

the IC to the PCB. It’s critical that the connection of the exposed pad to the PCB is properly constructed to maintain the desired IC case

temperature (TCB). A good connection ensures that temperature at the exposed pad (TCB) and the board temperature (TB) are relatively

the same. An improper connection can lead to increased junction temperature, increased power consumption and decreased electrical

performance. In addition, there could be long-term reliability issues and increased failure rate.

Example Calculation for Junction Temperature (TJ): TJ = TCB + JB x PD

For the variables above, the junction temperature is equal to 106.1oC. Since this is below the maximum junction temperature of 125oC,

there are no long term reliability concerns. In addition, since the junction temperature at which the device was characterized using forced

convection is 122oC, this device can function without the degradation of the specified AC or DC parameters.

Package type

48 VFQFN

Body size (mm)

7 x 7 x 0.8

ePad size (mm)

5.65 x 5.65

Thermal Via

5 x 5 Matrix



1.2oC/W

TCB

105oC

0.9W

TCB

8P34S2108NLGI Datasheet(PDF) 15 Page - Integrated Device Technology