APL5312-23 查看數據表（PDF） - Anpec Electronics

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APL5312-23

Ultra-Low-Noise, High PSRR, Low-Dropout, 300mA Linear Regulator

Anpec Electronics 

APL5312

Application Information (Cont.)

Noise, PSRR, and Load-Transient Response

(Cont.)

techniques (see the Figure Output Noise vs. BP

Capacitance).

Shutdown

The APL5312 has an active high enable function. Force

SHDN high (>1.6V) enables the V , SHDN low (<0.4V)

OUT

disables the VOUT. Enter the shutdown mode, it also

causes the output voltage to discharge through a 500Ω

resistance to ground. In shutdown mode, the

quiescent current can reduce to 0.1uA. The SHDN

pin cannot be floating, a floating SHDN pin may cause

an indeterminate state on the output. If it is no use,

connect to V for normal operation.

IN

Input-Output (Dropout) Voltage

The minimum input-output voltage differential (dropout)

determines the lowest usable supply voltage. The

dropout voltage is a function of drain-to-source on

resistance multiplied by the load current.

Current Limit

APL5312 includes a current-limit circuitry for linear

regulator. The current limit protection, which sense

the current flows the P-channel MOSFET, and con-

trols the output voltage. The point where limiting oc-

curs is IOUT = 500mA . The output can be shorted to

ground for an indefinite amount of time without damaging to

the part.

Thermal Protection

Thermal protection limits total power dissipation in the

APL5312. When the junction temperature exceeds

TJ = +160°C, the thermal sensor generate a logic sig-

nal to turn off the pass element and let IC to cool.

When the IC’s junction temperature cools by 20°C,

the thermal sensor will turn the pass element on again,

resulting in a pulsed output during continuous thermal

protection. Thermal protection is designed to protect

the IC in the event of fault conditions.

Operating Region and Power Dissipation

The thermal resistance of the case and circuit board,

ambient and junction air temperature, and the rate of

air flow all control the APL5312’s maximum power

dissipation. The power dissipation across the device

is P = IOUT (VIN-VOUT). The maximum power dissipation

is:

PMAX = (TJ - TA) / (θJC + θCA )

θJA = θJC + θCA

where TJ- TA is the temperature difference between the

junction and ambient air.

θJC is the thermal resistance of the package, θCA is the

thermal resistance through the printed circuit board,

copper traces, and other materials to the surrounding

air, θJA = is the thermal resistance between Junction

and ambient air. For continual operation, do not exceed

the absolute maximum junction Temperature rating of

T = 125°C.

J

For example:

The SOT23-5 package has maximum power dissipation

300mW at TA= 55°C, relatively 225mW at SC70-5

package (see the Figure Maximum Power Dissipation

vs. Ambient Temperature).

V = 5V, I = 250mA, V = 3.3V,

IN

OUT

OUT

PD = (5-3.3)V x 150mA = 255mW

According the power dissipation issue, we should adapt

the SOT23-5 package. It could reduce the thermal

resistance to maintain the IC longer life.

The GND pin provides an electrical connection to

ground and channeling heat away. The printed circuit

board (PCB) forms a heat sink and dissipates most of

the heat into ambient air.

Copyright © ANPEC Electronics Corp.

10

Rev. A.1 - Sep., 2005

www.anpec.com.tw

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