TPS54260_1 Datasheet, PDF (39/47 Pages) Texas Instruments – 3.5V to 60V INPUT, 2.5A, STEP DOWN CONVERTER WITH ECO-MODE™

TPS54260
www.ti.com
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).
Pcon = Io²
´ R_DS(on)
´
Vout
Vin
(49)
Psw = Vin ² ´ ¦sw ´ lo ´ 0.25 ´ 10^-9
(50)
Pgd = Vin ´ 3 ´ 10^-9 ´ ¦sw
(51)
Pq = 116 ´ 10^-6 ´ Vin
(52)
Where:
IOUT is the output current (A).
R_DS(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)
For given T_A,
TJ = TA + Rth ´ Ptot
(54)
For given T_JMAX = 150°C
TAmax = TJmax - Rth ´ Ptot
(55)
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_JMAX is maximum junction temperature (°C).
T_AMAX 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.
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