SP6203 Datasheet, PDF (8/14 Pages) Sipex Corporation – Low Noise, 300mA and 500mA CMOS LDO Regulators

General Overview
The SP6203/6205 is intended for applications
where very low dropout voltage, low supply
current and low output noise are critical, even
with high load conditions (500mA maximum).
Unlike bipolar regulators, the SP6203/6205
(CMOS LDO) supply current increases only
slightly with load current.
The SP6203/6205 contains an internal bandgap
reference which is fed into the inverting input of
the LDO-amplifier. The output voltage is then
set by means of a resistor divider and compared
to the bandgap reference voltage. The error
LDO-amplifier drives the gate of a P-channel
MOSFET pass device that has a R_DS(ON) of 0.6Ω
at 500mA producing a 300mV drop at the out-
put.
Furthermore, the SP6203/6205 has its own cur-
rent limit circuitry (500mA/850mA) to ensure
that the output current will not damage the
device during output short, overload or start-up.
Also, the SP6203/6205 includes thermal shut-
down circuitry to turn off the device when the
junction temperature exceeds 170°C and it re-
mains off until the temperature drops by 12°C.
Enable/Shutdown Operation
The SP6203/6205 is turned off by pulling the
V_EN pin below 0.4V and turned on by pulling it
above 1.6V.
If this enable/shutdown feature is not required,
it should be tied directly to the input supply
voltage to keep the regulator output on at all
time.
While in shutdown, V_OUT quickly falls to zero
(turn-off time is dependent on load conditions
and output capacitance on V_OUT) and power
consumption drops nearly to zero.
Input Capacitor
A small capacitor of 2.2µF is required from V_IN
to GND if a battery is used as the power
source. Any good quality electrolytic, ceramic
or tantalum capacitor may be used at the input.
THEORY OF OPERATION
Output Capacitor
An output capacitor is required between V_OUT
and GND to prevent oscillation. A 2.2µF output
capacitor is recommended.
Larger values make the chip more stable which
means an improvement of the regulator’s tran-
sient response. Also, when operating from other
sources than batteries, supply-noise rejection
can be improved by increasing the value of the
input and output capacitors and using passive
filtering techniques.
For a lower output current, a smaller output
capacitance can be chosen.
Finally, the output capacitor should have an
effective series resistance (ESR) of 0.5Ω or less.
Therefore, the use of good quality ceramic or
tantalum capacitors is advised.
Bypass Capacitor
A bypass pin (BYP) is provided to decouple the
bandgap reference. A 10nF external capacitor
connected from BYP to GND reduces noise
present on the internal reference, which in turn
significantly reduces output noise and also im-
proves power supply rejection. Note that the
minimum value of C_OUT must be increased to
maintain stability when the bypass capacitor is
used because C_BYP reduces the regulator phase
margin. If output noise is not a concern, this
input may be left unconnected. Larger capacitor
values may be used to further improve power
supply rejection, but result in a longer time
period (slower turn on) to settle output voltage
when power is initially applied.
No Load Stability
The SP6203/6205 will remain stable and in
regulation with no external load (other than the
internal voltage driver) unlike many other volt-
age regulators. This is especially important in
CMOS RAM battery back-up applications.
Date: 05/25/04
SP6203/6205 Low Noise, 300 and 500mA CMOS LDO Regulators
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© Copyright 2004 Sipex Corporation