Design Specification

300mA Low Noise Dual LDO

PL2211

OPERATION DESCRIPTION

The PL2211 are ultra-low-noise, low-dropout, low-

quiescent current linear regulators designed for space-

restricted applications. These devices can supply loads up

to 300mA. As shown in the Block Diagram, the PL2211

consists of a highly accurate band gap core, noise bypass

circuit, error amplifier, P-channel pass transistor and an

internal feedback voltage divider. The 1.0V band gap

reference is connected to the error amplifier’s inverting

input. The error amplifier compares this reference with

the feedback voltage and amplifies the difference. If the

feedback voltage is lower than the reference voltage, the

pass transistor gate is pulled low. This allows more

current to pass to the output and increases the output

voltage. If the feedback voltage is too high, the pass

transistor gate is pulled high, allowing less current to

pass to the output. The output voltage is feedback

through an internal resistor voltage divider connected to

the OUT pin. An external bypass capacitor connected to

BYP reduces noise at the output. Additional blocks

include a current limiter, over temperature protection,

and shutdown logic.

Internal P-Channel Pass Transistor

The PL2211 feature a 1

Ω (typ) P-channel MOSFET pass

transistor. This provides several advantages over similar

designs using a PNP pass transistor, including longer

battery life. The P-channel MOSFET requires no base

drive, which considerably reduces quiescent current.

PNP-based regulators waste considerable current in

dropout when the pass transistor saturates. They also use

high base-drive current under heavy loads. The PL2211

does not suffer from these problems and consume only

200

µA of quiescent current in light load.

Current Limit

The PL2211 includes a current limiter. It monitors the

output current and controls the pass transistor’s gate

voltage to limit the output current under 550mA (typ).

The output can be shorted to ground for an indefinite

amount of time without damaging the part.

Enable Input

The PL2211 features an active-high Enable input (EN)

pin that allows on/off control of the regulator. The

PL2211 bias current reduces to less than microampere of

leakage current when it is shutdown. The Enable input is

TTL/CMOS compatible threshold for simple logic

interfacing. When EN is ‘H,’ the output voltage startup

rising time is 35us typically at 300mA output current.

Connect EN pin to IN pin for normal operation

Under Voltage Lockout

When the input supply goes too low (below 2.0V) the

PL2211 produces an internal UVLO (under voltage

lockout) signal that generates a fault signal and shuts

down the chip. This mechanism protects the chip from

producing false logic due to low input supply.

Quick Charging Mode

The PL2211 has a quick charge block to get the reference

up very quickly by charging the BYP capacitor with very

high current when the chip comes out of shut down. This

quick charge block stops charging the BYP capacitor

when the reference reaches 95% of its nominal value and

then the chip switches out of quick charging mode to

normal operating mode.

Over Temperature Protection

Over

temperature

protection

limits

total

power

dissipation

in

the

PL2211.

When

the

junction

signals the shutdown logic and turns off the pass

transistor. The thermal sensor turns the pass transistor on

°C,

resulting in a pulsed output during continuous thermal-

overload conditions.

Thermal-Overload protection is design to protect the

PL2211 in the event of a fault condition. For continual

operation, do not exceed the absolute maximum junction

temperature rating of Tj = +150

°C.

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

Power IC Ltd.

- 5 -

www.picsemi.com

Version 1.0

Mar 4, 2007