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If the RS7103 uses a SOT‐25 package and this package is mounted on a double sided printed circuit board with two square
inches of copper allocated for “heat spreading”, the resulting θ
JA
is 180°C/W.
Based on a maximum operating junction temperature 125°C with an ambient of 25°C, the maximum power dissipation will be:
(
T
J
−
T
A
) (
125
−
25
)
P
MAX
=
=
=
0
.
40W
250
θ
JC
+
θ
CA
Thermal characteristics were measured using a double‐side board with 1”x 2” square inches of copper area connected to the
GND pin for “heat spreading”.
Dropout Voltage
A regulator’s minimum input‐output voltage differential, or dropout voltage, determines the lowest usable supply voltage. In
battery‐powered systems, this will determine the useful end‐of‐life battery voltage. The RS7103 uses a P‐channel MOSFET
pass transistor, its dropout voltage is a function of drain‐to‐source on‐resistance (R
DS(ON)
) multiplied by the load current.
V
DROPOUT
=
V
IN
−
V
OUT
=
R
DS
(
ON
)
×
I
OUT
DS‐RS7103‐02
September, 2009
www.Orister.com
ORISTER [ ORISTER CORPORATION ]
