Datasheet

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0 0.5 1 1.5 2 2.5 3 3.5
P -PowerDissipated-W
D
T -JunctionTemperature-°C
J
T =roomtemperature,noairflow
A
TPS54218
www.ti.com SLVS974B –SEPTEMBER 2009–REVISED JULY 2013
POWER DISSIPATION ESTIMATE
The following formulas show how to estimate the IC power dissipation under continuous conduction mode (CCM)
operation. The power dissipation of the IC (Ptot) includes conduction loss (Pcon), dead time loss (Pd), switching
loss (Psw), gate drive loss (Pgd) and supply current loss (Pq).
Pcon = I
OUT
2
× R
DS(on)
Pd = ƒsw × I
OUT
× 0.7 × 60 × 10
-9
Psw = 2 × V
IN
2
× ƒsw × I
OUT
× 0.25 × 10
-9
Pgd = 2 × V
IN
× 3 × 10
-9
× ƒsw
Pq = 350 × 10
-6
× V
IN
Where:
I
OUT
is the output current (A).
R
DS(on)
is the on-resistance of the high-side MOSFET (Ω).
V
OUT
is the output voltage (V).
V
IN
is the input voltage (V).
ƒsw is the switching frequency (Hz).
So
Ptot = Pcon + Pd + Psw + Pgd + Pq
For given T
A
,
T
J
= T
A
+ Rth × Ptot
For given T
J
max = 150°C
T
A
max = T
J
max – Rth × Ptot
Where:
Ptot is the total device power dissipation (W).
T
A
is the ambient temperature (°C).
T
J
is the junction temperature (°C).
Rth is the thermal resistance of the package (°C/W).
T
J
max is maximum junction temperature (°C).
T
A
max 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 dissipation for the EVM is shown in Figure 52.
Figure 51. Junction Temperature vs IC Power Dissipation
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