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

600mA (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

sensor signals the shutdown logic and turns off the

pass transistor. The thermal sensor turns the pass

transistor on again after the IC’s junction

temperature drops by 20

°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.

July 2007

www.picsemi.com

© 2007 Power IC. All Rights Reserved.

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