Design Specification

300mA Low Noise Dual LDO

PL2211

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 = 0.01µF

and Cout = 1

µF.

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 70dB at 100Hz and 60dB 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).

Power IC Ltd.

- 6 -

www.picsemi.com

Version 1.0

Mar 4, 2007