Datasheet

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Tj-JunctionTemperature
PowerDissapated(W)
Ta=roomtemperature,noairflow
TPS54418
SLVS946C –MAY 2009–REVISED JULY 2013 www.ti.com
ƒsw is the switching frequency (Hz).
So
Ptot = Pcon + Pd + Psw + Pgd + Pq
For given TA,
TJ = TA + Rth × Ptot
For given TJMAX = 150°C
TAmax = TJ max – Rth × Ptot
Where:
Ptot is the total device power dissipation (W).
TA is the ambient temperature (°C).
TJ is the junction temperature (°C).
Rth is the thermal resistance of the package (°C/W).
TJMAX is maximum junction temperature (°C).
TAMAX is maximum ambient temperature (°C).
There are additional power losses in the regulator circuit due to the inductor AC and DC losses and trace
resistance that impact the overall efficiency of the regulator. As an example, the maximum ambient temperature
versus power dissapation for the EVM is shown in Figure 52.
Figure 51. Junction Temperature vs IC Power Dissipation
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