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 1Ω (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
200μA 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
temperature exceeds T
j
= +165°C, the thermal
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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