Datasheet

TAmax = TJmax Rth Ptot- ´
TJ = TA + Rth Ptot´
Ptot = Pcon + Psw + Pgd + Pq
6
Pq = 116 10 Vin
-
´ ´
9
Pgd = Vin 3 10 sw
-
´ ´ ´ ¦
2 9
Psw = Vin sw lo 0.25 10
-
´ ¦ ´ ´ ´
2
DS(on)
Vout
Pcon = Io R
Vin
´ ´
TPS57040-Q1
www.ti.com SLVSAP4C –DECEMBER 2010–REVISED OCTOBER 2012
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 (P
con
), switching loss (P
sw
), gate drive loss (P
gd
) and
supply current (P
q
).
(49)
(50)
(51)
(52)
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).
ƒ
SW
is the switching frequency (Hz).
So
(53)
For given T
A
,
(54)
For given T
JMAX
= 150°C
(55)
Where:
P
tot
is the total device power dissipation (W).
T
A
is the ambient temperature (°C).
T
J
is the junction temperature (°C).
R
th
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.
Copyright © 2010–2012, Texas Instruments Incorporated Submit Documentation Feedback 39
Product Folder Links: TPS57040-Q1