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 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.
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 75dB at 100Hz and 70dB at 10kHz
(see the Power-Supply Rejection Ratio vs.
Frequency graph in the Typical Characteristic).
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
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).
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
July 2007
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© 2007 Power IC. All Rights Reserved.
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