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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 θJA 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 )
PMAX
=
=
= 0.40W
θ
JC + θCA
250
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 (RDS(ON)) multiplied by the load current.
VDROPOUT =VIN −VOUT = RDS (ON ) × IOUT
DS‐RS7103‐02 September, 2009
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