Operating Region and Power Dissipation

The PL2211 maximum power dissipation depends

on 1) the thermal resistance of the case and circuit

board, 2) the temperature difference between the

die junction and ambient, and 3) the rate of airflow.

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 PL2211 die junction and the ambient

air;

θjc is the thermal resistance of the package;

and

θca is the thermal resistance through the PC

board, copper traces, and other materials to the

surrounding air.

The GND pin of the PL2211 performs the dual

function of providing an electrical connection to

ground and channeling heat away. Connect the

GND pin to ground using a large pad or ground

plane.

Noise Reduction

For the PL2211, an external 0.01

μF bypass

capacitor between BYP and GND with innovative

noise bypass scheme reduces output noises

dramatically, exhibiting 100

μVrms of output voltage

noise with Cbyp = 0.01

μF and Cout = 1μF.

APPLICATION INFORMATION

Capacitor Selection and Regulator Stability

Use a 1

μF capacitor on the PL2211 input and a 1μF

capacitor on the output. Large input capacitor

values and lower ESRs provide better noise

rejection and line-transient response.

Reduce output noise and improve load-transient

response, stability, and power-supply rejection by

using large output capacitors. Note that some

ceramic dielectrics exhibit large capacitance and

ESR variation with temperature. With dielectrics

such as Z5U and Y5V, it may be necessary to use a

1

μF or larger output capacitor to ensure stability at

temperatures below -10

°C. With X7R or X5R

dielectrics, 1

μF is sufficient at all operating

temperatures. A graph of the region of stable Cout

ESR vs. load current is shown in the Typical

Characteristics.

Use a 0.01

μF bypass capacitor at BYP for low-

output voltage noise. The leakage current going

into the BYP pin should be less than 10nA.

Noise, PSRR, and Transient Response

The PL2211 are designed to deliver ultra-low noise

and high PSRR, as well as low dropout and low

quiescent currents in battery-powered systems. The

PL2211 PSRR is 75dB at 100Hz and 70dB at 10kHz

(see

the

Power-Supply

Rejection

Ratio

vs.

Frequency graph in the Typical Characteristic).

When operating from sources other than batteries,

improved supply-noise rejection and transient

response can be achieved by increasing the values

of the input and output bypass capacitors, and

through passive filtering techniques. The Typical

Characteristics show the PL2211 line and load

transient responses.

Dropout Voltage

A regulator’s minimum dropout voltage determines

the lowest usable supply voltage. In battery-

powered systems, this determines the useful end-

of-life battery voltage. Because the PL2211 use a P-

channel MOSFET pass transistor, their dropout

voltage is a function of drain-to-source on

resistance (RDS (on)) multiplied by the load current

(see the Typical Characteristics).

July 2007

www.picsemi.com

© 2007 Power IC. All Rights Reserved.

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