SP6205EM5-L-3-3-TR Datasheet, PDF (9/15 Pages) Exar Corporation – 300mA/500mA Low Noise CMOS LDO Regulators

SP6203 / SP6205
300mA/500mA Low Noise CMOS LDO Regulators
THEORY OF OPERATION
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 output.
Furthermore, the SP6203/6205 has its own
current 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.
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 transient 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 improves 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
voltage regulators. This is especially important
in CMOS RAM battery back-up applications.
TURN ON TIME
The turn on response is split up in two
separate response categories: the wake up
© 2012 Exar Corporation
9/14
Rev. 2.0.0