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PAM3103 Datasheet, PDF (7/10 Pages) Power Analog Micoelectronics – 300mAAdjustable High PSRR CMOS Linear Regulator
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PAM3103
300mA Adjustable High PSRR CMOS Linear Regulator
Thermal considerations
Thermal protection limits power dissipation in the
PAM3103. When the junction temperature
exceeds 150°C, the OTP (Over Temperature
Protection) starts the thermal shutdown and turns
the pass transistor off. The pass transistor
resumes operation after the junction temperature
drops below 120°C.
For continuous operation, the junction
temperature should be maintained below 125°C.
The power dissipation is defined as below:
PD= (V -IN V ) OUT *IO+V *IN IGND
The maximum power dissipation depends on the
thermal resistance of IC package, PCB layout,
the rate of surrounding airflow and temperature
difference between junction and ambient. The
maximum power dissipation can be calculated by
the following formula:
PD(MAX) = (TJ(M - AX) TA)/θJA
Where TJ(MAX) is the maximum allowable junction
temperature 125°C, TAis the ambient temperature
and θJA is the thermal resistance from the junction
to the ambient.
For example, as θJA is 250°C/W for the SOT-23
package based on the standard JEDEC 51-3 for
a single-layer thermal test board, the maximum
power dissipation at TA=25°C can be calculated
by following formula:
P = D(MAX) (125°C-25°C)/250=0.4W
It is also useful to calculate the junction
temperature of the PAM3103 under a set of
specific conditions. Suppose the input voltage
VIN=3.3V, the output current IO=300mA and the
case temperature TA=40°C measured by a
thermal couple during operation, the power
dissipation is defined as:
PD=(3.3V-2.8V)*300mA+3.3V*70uA≌150mW
And the junction temperature TJ can be
calculated as follows:
TJ = TA+PD*θJA
TJ= 40°C+0.15W*250°C/W
=40°C+37.5°C
=77.5°C<TJ(MAX) = 125°C
For this application, TJ is lower than the absolute
maximum operating junction temperature
125°C, so it is safe to use the PAM3103 in this
configuration.
Power Analog Microelectronics,Inc
www.poweranalog.com
7
09/2008 Rev 1.2
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