PL0501
OPERATION
The PL0501 is an ultra-low-noise, low-dropout, low-
quiescent current linear regulator designed for space-
restricted applications. It is available with preset output
voltages ranging from 1.5V to 5.0V in 100mV increments.
It can supply loads of up to 500mA. As shown in the
Block Diagram, the PL0501 consists of a highly accurate
band gap core, noise bypass circuit, error amplifier, P-
channel pass transistor and an internal feedback voltage
divider. The PL0501 allows for an adjustable output with
an external feedback network. 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 fed back
through an internal resistor voltage-divider connected to
the OUT pin. An external bypass capacitor connected to
BYP (PL0501-BYP) reduces the noise at the output.
To set the output of the PL0501, use the following
equation:
VOUT = VREF × [1 + (R1/R2)]
Where
R2 is chosen to be less than 240KΩ
and VREF = 1.0V. Use 1% or better
resistors.
Current Limit
The PL0501 includes a current limiter. It monitors the
output current and controls the pass transistor’s gate
voltage to limit the output current under 1500mA
(typical). The output can be shorted to ground for an
indefinite amount of time without damaging the part.
The short circuit current limit is increased to
approximately 1500mA (typical) when the output voltage
is within 10% of the nominal output, thus improving the
performance of large pulsating loads. The in-regulation
current limit option provides the user to overload the
device, maintaining a continuous 500mA (RMS) load.
Additional blocks include
a
current limiter, over
temperature protection and shutdown logic.
Enable Input
The PL0501 features an active-high Enable input (EN)
pin that allows on/off control of the regulator. The
PL0501 bias current reduces to ZERO (leakage current)
when it goes into shutdown. The Enable input is
TTL/CMOS compatible for simple logic interfacing. When
EN is ‘H,’ the output voltage startup rising time is typically
25µs. Connect EN pin to IN pin for normal operation.
Internal P-Channel Pass Transistor
The PL0501 features a 1Ω (typical) 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 the 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.
Power Good Flag
The PL0501 features a Power Good flag (PGD), which
monitors the output voltage and signals an error
condition when the output voltage drops 10% below its
nominal value.
The PL0501 does not suffer from these problems and
consumes only 90μA of quiescent current.
Output Voltage Selection
The PL0501 is supplied with factory-set output voltages
from 1.5V to 5.0V, in 100mV increments. The PL0501
features a user-adjustable output through an external
feedback network (see Typical Application).
Under Voltage Lockout
When the input supply goes too low (typically below
2.0V), the PL0501 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.
7
July 2007
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