Datasheet

( )
( )
( )
( )
J A
Q
JA IN
SW
g
T T
I
V
f Hz
2 Q
æ ö
é ù
-
-
ç ÷
ê ú
ç ÷
q ´
ê ú
ë û
è ø
=
´
P
T
+
ƪǒ
2 Q
g
f
SW
Ǔ
) I
Q
ƫ
V
IN
(W)
P
T
+
ǒ
2 P
D
V
DR
) I
Q
Ǔ
V
IN
(W)
D g DR SW
P Q V f (W / driver)= ´ ´
TPS40060
TPS40061
www.ti.com SLUS543F –DECEMBER 2002–REVISED JUNE 2013
TPS40060/TPS40061 POWER DISSIPATION
The power dissipation in the TPS40060 and TPS40061 is largely dependent on the MOSFET driver currents and
the input voltage. The driver current is proportional to the total gate charge, Qg, of the external MOSFETs. Driver
power (neglecting external gate resistance, (refer to the second reference in the REFERENCES section) can be
calculated from Equation 38.
(38)
And the total power dissipation in the device, assuming MOSFETs with similar gate charges for both the high-
side and synchronous rectifier is described in Equation 39.
(39)
or
where:
• I
Q
is the quiescent operating current (neglecting drivers) (40)
The maximum power capability of the device's PowerPad package is dependent on the layout as well as air flow.
The thermal impedance from junction to air, assuming 2 oz. copper trace and thermal pad with solder and no air
flow.
Θ
JA
= 36.51°C/W
The maximum allowable package power dissipation is related to ambient temperature by Equation 36.
Substituting Equation 32 into Equation 40 and solving for f
SW
yields the maximum operating frequency for the
TPS40060 and TPS40061. The result is:
(41)
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