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| TPS5401EVM-708 Datasheet, PDF (33/41 Pages) Texas Instruments – 0.5-A, 42-V Input, Step-Down SWIFT™ Converter | |||
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TPS5401
www.ti.com
SLVSAB0 â DECEMBER 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 (PSUP).
Pcon = IOUT2 ´ rDS(on) ´
VOUT
VIN
(36)
Psw = VIN2 ´ lOUT ´ 0.25 ´ 10-9 ´ fSW
(37)
PGD = VIN ´ 3 ´ 10-9 ´ fSW
(38)
PSUP = 116 ´ 10-6 ´ VIN
(39)
So total power dissipation is:
PTOT = PCON + PSW + PGD + PSUP
(40)
For a given ambient temperature TA, the junction temperature TJ can be estimated by Equation 41.
TJ = TA -qJA ´PTOT
(41)
where:
⢠qJA is the thermal resistance of the package (°C/W)
For given TJ(max) = 150°C, the maximum allowed ambient temperature can be estimated by Equation 42.
TA(max) = TJ(max) - qJA ´ PTOT
(42)
There are additional power losses in the regulator circuit due to the inductor ac and dc losses, the catch diode
and trace resistance that impact the overall efficiency of the regulator.
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): TPS5401
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