APL5101-35AI datasheet(9/15 Pages) ANPEC

9 / 15 page

Rev. A.1 - Jun., 2005

APL5101/2

www.anpec.com.tw

Application Information

Capacitor Selection and Regulation Stability

The APL5101/2 use at least a 1

µF capacitor on the

input. This capacitor can use Aluminum, Tantalum or

Ceramic capacitors. Input capacitor with large value

and low ESR provides better PSRR and line transient

response. The output capacitor also can use Aluminum,

Tantalum or Ceramic capacitor, and its proper values

is recommended 1

µF, ESR must be above 10mΩ

Large output capacitor values can reduce noise and

improve load-transient response, stability, and PSRR.

With X5R and Y5V dielectrics, 1

µF is sufficient at all

operating temperatures. The selection of output capacitor

is important because it with COUT form a zero to provide

the sufficient phase margin.

Input-Output (Dropout) Voltage

Theminimum 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 and Short Circuit

APL5101/2 include a current-limit circuitry for this

linear regulator. The current limit protection, which

sense the current flows the P-channel MOSFET, and

controls the output voltage. The point where limiting

occurs is IOUT=300mA. When output is shorted to

ground, the APL5101/2 will keep short circuit current

at 50mA .This design is a method for an indefinite

amount of time without damaging to the part.

Thermal Protection

Thermal protection limits total power dissipation in the

APL5101/2. When the junction temperature exceeds

TJ = +135

°C, the thermal sensor generate a logic signal

to turn off the pass transistor and let IC to cool.When

the IC’s junction temperature cools by 20

°C, the

thermal sensor will turn the pass transistor 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. For continual

operation, do not exceed the absolute maximum junction

temperature rating of TJ = +140

°C.

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 APL5101/2’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 )

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. 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.

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