L1923L-XX-AF5-R datasheet(6/7 Pages) UTC

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L1923

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

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www.unisonic.com.tw

QW-R502-440.c

APPLICATION INFORMATION (Cont.)

Shutdown Mode

The UTC L1923 enters shutdown mode if the SHDN pin is applied to a logic low voltage. Under the shutdown

state, all the analog circuits are turned off completely, which reduces the current consumption to only the leakage

current. The UTC L1923 output pass transistor would get into high impedance level. There is an internal discharge

path to help to shorten discharge delay time.

Operating Region and Power Dissipation

The UTC L1923 is a linear regulator, so the power dissipation can be expressed by: P = IOUT (VIN – VOUT). And the

maximum power dissipation is calculated by:

PD(MAX) = (TJ–TA)/θJA,=(150°C -25°C)/240°C/W= 520mW

(Where (TJ–TA) is the temperature difference the die and the ambient air; θJA, is the thermal resistance of the

chosen package to the ambient air.)

For surface mount device, heat sinking is accomplished by using the heat spreading capabilities of the PC board

and its copper traces. The die attachment area of the UTC L1923’s lead frame is connected to pin 2, which is the

GND pin. Therefore, the GND pin of UTC L1923 can carry away the heat of the UTC L1923 die very effectively.

Connecting the GND pin to ground using a large ground plane near the GND pin can improve the power

consumption.

Capacitor Selection and Regulator Stability

A 1µF capacitor on the input and a 4.7µF capacitor on the output are recommended for most applications of the U

TC L1923. To get a better supply-noise rejection and transient response, input capacitors with larger values and

lower ESR are needed. A higher-value input capacitor (10µF) may be necessary if large, fast transients are

anticipated and the device is located several inches from the power source.

Power-Supply Rejection and Operation from Sources Other than Batteries

The UTC L1923 is particularly designed to deliver low dropout voltages and low quiescent currents in battery-

powered systems. Power-supply rejection is 42dB at low frequencies. As the frequency increases above 20kHz, the

output capacitor is the major contributor to the rejection of power-supply noise.

When operating from sources other than batteries, improve supply-noise rejection and transient response by

increasing the values of the input and output capacitors, and using passive filtering techniques.

Input-Output (Dropout) Voltage

The minimum input-output voltage differential (or dropout voltage) of a regulator determines the lowest usable

supply voltage. In battery-powered system applications, this will determine the useful end-of-life battery voltage.

Because the UTC L1923 use a P-channel MOSFET pass transistor, their dropout voltage is a function of RDS(ON)

multiplied by the load current.

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