TS2938_07 Datasheet, PDF (4/7 Pages) Taiwan Semiconductor Company, Ltd – 500mA Ultra Low Dropout Voltage Regulator with Inhibit Function

TS2938
500mA Ultra Low Dropout Voltage Regulator
with Inhibit Function
Application Information
Application
The TS2938 series is a high performance with low dropout voltage regulator suitable for moderate to high current
and voltage regulator application. Its 500Mv (typ) dropout voltage at full load and over temperature makes it
especially valuable in battery power systems and as high efficiency noise filters in post regulator applications. Unlike
normal NPN transistor design, where the base to emitter voltage drop and collector to emitter saturation voltage limit
the minimum dropout voltage, dropout performance of the PNP output of these devices is limited only by low Vce
saturation voltage.
The TS2938 series is fully protected from damage due to fault conditions. Linear current limiting is provided. Output
current during overload conditions is constant. Thermal shutdown the device when the die temperature exceeds the
maximum safe operating temperature. Transient protection allows device survival even when the input voltage
spikes above and below nominal. The output structure of these regulators allows voltages in excess of the desired
output voltage to be applied without reverse current flow.
Output Capacitor
The TS2938 series requires an output capacitor to maintain stability and improve transient response. Proper
capacitor selection is important to ensure proper operation. The output capacitor selection is dependent upon the
ESR of the output capacitor the maintain stability. When the output capacitor is 6.8uF or greater, the output capacitor
should have an ESR less than 2 ohm. This will improve transient response as well as promoted stability. Ultra low
ESR capacitors (<100mohm), such as ceramic chip capacitors may promote instability. These very low ESR levels
may cause an oscillation and/or under damped transient response. A low ESR solid tantalum capacitor works
extremely well and provide good transient response and stability over temperature. Aluminum electrolytic can also be
used, as long as the ESR of the capacitor is <2ohm. The value of the output capacitor can be increased without limit.
Higher capacitance values help to improved transient response and ripple rejection and reduce output noise.
Minimum Load Current
The TS2938 series is specified between finite loads. If the output current is too small leakage currents dominate and
the output voltage rises. A 5mA minimum load current is necessary for proper regulation.
Input Capacitor
An input capacitor of 1uF or greater is recommended when the device is more that 4 inches away from the bulk AC
supply capacitance or when the supply is a battery. Small and surface mount ceramic chip capacitors can be used
for bypassing. Larger values will help to improve ripple rejection by bypassing the input to the regulator, further
improving the integrity of the output voltage.
Adjustable Regulator Design
The adjustable regulator versions is allow to programming the output voltage anywhere between 1.25 and the 26V
maximum operating rating of the family.
Two resistors are used. Resistors can be quite large up to 1MΩ, because of the very high input impedance and low
bias current of the sense comparator, the resistor values are calculated by:
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Version: A07