TS2938

500mA Ultra Low Dropout Voltage Regulator

with Inhibit Function

4/7

Version: A07

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: