UM4750_15 Datasheet, PDF (9/13 Pages) Union Semiconductor, Inc. – 300mA, Micropower, Dual Channel VLDO Linear Regulator

UM4750
Internal Current Limit
The UM4750 internal current limits help protect the regulator during fault conditions. During
current limit, the output sources a fixed amount of current that is largely independent of output
voltage. For reliable operation, the device should not be operated in a limit state for extended
periods of time.
The PMOS pass element in the UM4750 has a built-in body diode that conducts current when the
voltage at OUT exceeds the voltage at IN. This current is not limited, so if extended reverse
voltage operation is anticipated, external limiting to 5% of rated output current may be
appropriate.
Dropout Voltage
The UM4750 use a PMOS pass transistor to achieve low dropout. When (V_IN-V_OUT) is less than
the dropout voltage, the PMOS pass device is in its linear region of operation and the
input-to-output resistance is the R_DS of the PMOS pass element. V_DROP approximately scales with
output current because the PMOS device behaves like a resistor in dropout.
Thermal Protection
Thermal protection disables the output when the junction temperature rises to approximately
+150°C allowing the device to cool. When the junction temperature cools to approximately
+120°C the output circuit is again enabled. Depending on power dissipation, thermal resistance,
and ambient temperature, the thermal protection circuit may circle on and off. This cycling limits
the dissipation of the regulator, protecting it from damage due to overheating.
Thermal Considerations
Thermal protection limits power dissipation in UM4750. When the operation junction temperature
exceeds 150°C, the OTP circuit starts the thermal shutdown function and turns the pass element
off. The pass element turns on again after the junction temperature cools by 25°C. For continuous
operation, do not exceed absolute maximum operation junction temperature 125°C. The power
dissipation definition in device is:
P_D =(V_IN -V_OUT1)×I_OUT1 + (V_IN -V_OUT2)×I_OUT2 + V_IN×I_Q
The maximum power dissipation depends on the thermal resistance of IC package, PCB layout,
the rate of surroundings airflow and temperature difference between junctions to ambient. The
recommended maximum power dissipation of SOT23-6, DFN6 2.0×2.0 and DFN8 3.0×3.0
packages for 25°C ambient temperature are 0.5W, 0.7W and 0.9W.
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http://www.union-ic.com Rev.07 Nov.2015
9/13