Design Specification
300mA Low Noise Dual LDO
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 0.01µF bypass capacitor
between BYP and GND with innovative noise bypass
scheme reduces output noises dramatically, exhibiting
100µVrms of output voltage noise with Cbyp = 0.01µF
and Cout = 1µF.
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).
PL2211
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
APPLICATION INFORMATION
Capacitor Selection and Regulator Stability
Use a 1µF 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 1µF or larger output capacitor
to ensure stability at temperatures below -10°C. With
X7R or X5R dielectrics, 1µF 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 0.01µF 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).
Power IC Ltd.
Version 1.0
-6-
www.picsemi.com
Mar 4, 2007
PICSEMI [ POWER IC LTD. ]
