TS2938CSRL datasheet(4/6 Pages) TSC

4 / 6 page

TS2938

500mA Ultra Low Dropout Voltage Regulator

with Inhibit Function

4/6

Version: D07

Application Information (Continue)

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.

Thermal Characteristics

A heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of the

application. Under all possible operating conditions, the junction temperature must be within the range specified

under absolute maximum ratings. To determine if the heatsink is required, the power dissipated by the regulator, PD

must be calculated.

The below formula shows the voltages and currents for calculating the PD in the regulator:

IIN = IL / IG

PD = (VIN-VOUT) * IL + (VIN) * IG

Ex. PD = (3.3V-2.5V) * 0.5A + 3.3V * 11mA

= 400mW + 36mW

= 436mW

The next parameter which must be calculated the maximum allowable temperature rise.

TR(max) is calculated by the using to formula:

TR(max) = TJ(max) – TA(max)

Where: TJ(max) is the maximum allowable junction temperature, which is 125

oC for commercial grade parts. TA(max)

is the maximum ambient temperature which will be encountered in the application.

Using the calculated values for TA(max) and PD, the maximum allowable value for the junction to ambient thermal

resistance, θJA, can now be found:

θJA = TR(max) / PD

Inhibit Input

TS2938 feature an active-low (Inhibit) input that allows ON/OFF control of the regulator. The Inhibit input has

TTL/CMOS compatible thresholds for simple interfacing with logic interfacing. Inhibit should be directly tied to

Ground or keep open (not connected).

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