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If the RS7300 uses a SOT‐89 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 155°C/W.
Based on the maximum operating junction temperature 125°C with an ambient of 25°C, the maximum power dissipation will
be:
(TJ −TA)
θJC + θCA
(125 − 25 )
PMAX =
=
= 0.65W
155
Thermal characteristics were measured using a double sided board with 1”x2” 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 RS7300 use 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‐RS7300‐14 September, 2009
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