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SEMP8965 Datasheet(PDF) 11 Page - SeCoS Halbleitertechnologie GmbH

Part No. SEMP8965
Description  Fast Ultra High-PSRR, Low Noise, Low-Dropout
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Maker  SECOS [SeCoS Halbleitertechnologie GmbH]
Homepage  http://www.secosgmbh.com
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SEMP8965 Datasheet(HTML) 11 Page - SeCoS Halbleitertechnologie GmbH

 
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Elektronische Bauelemente
SEMP8965
Fast Ultra High-PSRR, Low Noise, Low-Dropout,
600 mA Micropower CMOS Linear Regulator
01-June-2002 Rev. A
Page 11 of 11
http://www.SeCoSGmbH.com/
Any changes of specification will not be informed individually.
POWER DISSIPATION AND THERMAL SHUTDOWN
Thermal overload results from excessive power dissipation that causes the IC junction temperature to increase beyond a safe operating level. The
SEMP8965 relies on dedicated thermal shutdown circuitry to limit its total power dissipation. An IC junction temperature TJ exceeding 165°C will
trigger the thermal shutdown logic, turning off the P-channel MOS pass transistor. The pass transistor turns on again after the junction cools off by
about 30°C. When continuous thermal overload conditions persist, this thermal shutdown action then results in a pulsed waveform at the output of
the regulator. The concept of thermal resistance θJA (°C/W) is often used to describe an IC junction’s relative readiness in allowing its thermal
energy to dissipate to its ambient air. An IC junction with a low thermal resistance is preferred because it is relatively effective in dissipating its
thermal energy to its ambient, thus resulting in a relatively low and desirable junction temperature. The relationship between θJA and TJ is as
follows:
TJ JA (PD) + TA
TA is the ambient temperature, and PD is the power generated by the IC and can be written as:
PD = IOUT (VIN - VOUT)
As the above equations show, it is desirable to work with ICs whose θJA values are small such that TJ does not increase strongly with PD. To avoid
thermally overloading the SEMP8965, refrain from exceeding the absolute maximum junction temperature rating of 150°C under continuous
operating conditions. Overstressing the regulator with high loading currents and elevated input-to-output differential voltages can increase the IC
die temperature significantly.
FAULT DETECTION
In the event of the occurrence of various fault conditions that cause failure in the output voltage regulation, such as during thermal overload or
current limit, the FAULT pin of the SEMP8965 becomes low. Because the FAULT pin connects to the open-drain output of a N-channel MOS
transistor, a large pull-up resistor (100kΩ typical) is required to provide the necessary output voltage and yet without compromising the overall
power consumption performance of the regulator. The FAULT pin also goes low when the input-to-output differential voltage becomes too small to
sustain good load and line regulation at the output. This occurs typically during near dropout when the input-to-output differential voltage is less
than 110mV for a load current of 200mA. The SEMP8965 detects near dropout conditions by comparing the differential voltage against a
predefined differential threshold that is always slightly above the dropout voltage. This differential threshold is dynamical in the sense that it not only
tracks the dropout voltage as the load current varies, but also scale linearly with the load current.
SHUTDOWN
The SEMP8965 enters the sleep mode when the SHDN pin is low. When this occurs, the pass transistor, the error amplifier, and the biasing
circuits, including the bandgap reference, are turned off, thus reducing the supply current to typically 1nA. Such a low supply current makes the
SEMP8965 best suited for battery-powered applications. The maximum guaranteed voltage at the SHDN pin for the sleep mode to take effect is
0.4V. A minimum guaranteed voltage of 1.2V at the SHDN pin will activate the SEMP8965. Direct connection of the SHDN pin to the VIN to keep
the regulator on is allowed for the SEMP8965. In this case, the SHDN pin must not exceed the supply voltage VIN.
FAST START-UP
Fast start-up time is important for overall system efficiency improvement. The SEMP8965 assures fast start-up speed when using the optional
noise bypass capacitor (CC). To shorten start-up time, the SEMP8965 internally supplies a 500µA current to charge up the capacitor until it reaches
about 90% of its final value.


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