TPS54260
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SLVSA86 –MARCH 2010
Power Dissipation Estimate
The following formulas show how to estimate the IC power dissipation under continuous conduction mode (CCM)
operation. These equations should not be used if the device is working in discontinuous conduction mode (DCM).
The power dissipation of the IC includes conduction loss (Pcon), switching loss (Psw), gate drive loss (Pgd) and
supply current (Pq).
Vout
´
Pcon = Io2 ´ RDS(on)
Vin
(49)
(50)
(51)
(52)
Psw = Vin 2 ´ ¦sw ´ lo ´ 0.25 ´ 10-9
Pgd = Vin ´ 3 ´ 10-9 ´ ¦sw
Pq = 116 ´ 10-6 ´ Vin
Where:
IOUT is the output current (A).
RDS(on) is the on-resistance of the high-side MOSFET (Ω).
VOUT is the output voltage (V).
VIN is the input voltage (V).
fsw is the switching frequency (Hz).
So
Ptot = Pcon + Psw + Pgd + Pq
(53)
(54)
(55)
For given TA,
TJ = TA + Rth ´ Ptot
For given TJMAX = 150°C
TAmax = TJmax - 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 will be additional power losses in the regulator circuit due to the inductor ac and dc losses, the catch diode
and trace resistance that will impact the overall efficiency of the regulator.
Copyright © 2010, Texas Instruments Incorporated
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