LP2950-N, LP2951-N
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SNVS764Q –JANUARY 2000–REVISED DECEMBER 2017
8.3 Feature Description
8.3.1 Fixed Voltage Options and Programmable Voltage Version
The LP2950-N and LP2951-N provide 3 fixed output options: 3 V, 3.3 V, and 5 V. Please consult factory for
custom voltages. In order to meet different application requirements, LP2951-N can also be used as a
programmable voltage regulator, with an external resistors network; please refer to Application and
Implementation for more details.
8.3.2 High Accuracy Output Voltage
With special carful design to minimize all contributions to the output voltage error, the LP2950-N/LP2951-N
distinguished itself as a very high output voltage accuracy micro power LDO. This includes a tight initial tolerance
(0.5% typical), extremely good load and line regulation (.05% typical) and a very low output voltage temperature
coefficient, making the part an ideal a low-power voltage reference.
8.3.3 Low Dropout Voltage
Generally speaking, the dropout voltage often refers to the voltage difference between the input and output
voltage (VDO = VIN – VOUT), where the main current pass-FET is fully on in the ohmic region of operation and is
characterized by the classic RDS(ON) of the FET. VDO indirectly specifies a minimum input voltage above the
nominal programmed output voltage at which the output voltage is expected to remain within its accuracy
boundary.
8.3.4 Shutdown Mode
When the SHUTDOWN pin is pulled to high level, LP2951-N enters shutdown mode and a very low quiescent
current is consumed. This function is designed for the application which needs a shutdown mode to effectively
enhance battery life cycle.
8.3.5 Error Detection Comparator Output
The LP2951-N generates a logic low output whenever its output falls out of regulation by more than
approximately 5%. Please refer to Application and Implementation for more details.
8.3.6 Internal Protection Circuitry
8.3.6.1 Short-Circuit Protection (Current Limit)
The internal current limit circuit is used to protect the LDO against high-load current faults or shorting events. The
LDO is not designed to operate in a steady-state current limit. During a current-limit event, the LDO sources
constant current. Therefore, the output voltage falls when load impedance decreases. Note also that if a current
limit occurs and the resulting output voltage is low, excessive power may be dissipated across the LDO, resulting
in a thermal shutdown of the output. A fold back feature limits the short-circuit current to protect the regulator
from damage under all load conditions. If OUT is forced below 0 V before EN goes high and the load current
required exceeds the fold back current limit, the device may not start up correctly.
8.3.6.2 Thermal Protection
The device contains a thermal shutdown protection circuit to turn off the output current when excessive heat is
dissipated in the LDO. The thermal time-constant of the semiconductor die is fairly short, and thus the output
cycles on and off at a high rate when thermal shutdown is reached until the power dissipation is reduced. The
internal protection circuitry of the device is designed to protect against thermal overload conditions. The circuitry
is not intended to replace proper heat sinking. Continuously running the device into thermal shutdown degrades
its reliability.
8.3.7 Enhanced Stability
The LP2950-N and LP2951-N is designed specifically to work with ceramic output capacitors, utilizing circuitry
which allows the regulator to be stable across the entire range of output current with an output capacitor whose
ESR is as low as 6 mΩ. For output capacitor requirement, please refer to Application and Implementation.
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