SP6201EM5 Datasheet, PDF (12/17 Pages) Exar Corporation – 100mA/200mA Micropower CMOS LDO Regulators

SP6200 / SP6201
100mA/200mA Micropower CMOS LDO Regulators
Fig. 40: Power Supply Rejection Ratio
Fig. 41: Power Supply Rejection Ratio
THEORY OF OPERATION
GENERAL OVERVIEW
The SP6200 and SP6201 are CMOS LDOs
designed to meet a broad range of
applications that require accuracy, speed and
ease of use. These LDOs offer extremely low
quiescent current which only increases slightly
under load, thus providing advantages in
ground current performance over bipolar
LDOs. The LDOs handle an extremely wide
load range and guarantee stability with a 1μF
ceramic output capacitor. They have excellent
low frequency PSRR, not found in other CMOS
LDOs and thus offer exceptional Line
Regulation. High frequency PSRR is better
than 40dB up to 400kHz. Load Regulation is
excellent and temperature stability is
comparable to bipolar LDOs. Thus, overall
system accuracy is maintained under all DC
and AC conditions. Enable feature is provided
on all versions. A Vout good indicator (RSN
pin) is provided in all the fixed output voltage
devices. An adjustable output version is also
available. Current Limit and Thermal
protection is provided internally and is well
controlled.
ARCHITECTURE
The SP6200 and SP6201 are only different in
their current limit threshold. The SP6200 has a
current limit of 140mA, while the SP6201
current limit is 420mA. The SP6201 can
provide pulsed load current of 300mA. The
LDOs have a two stage amplifier which
handles an extremely wide load range (10μA
to 300mA) and guarantees stability with a 1μF
ceramic load capacitor. The LDO amplifier has
excellent gain and thus touts PSRR
performance not found in other CMOS LDOs.
The amplifier guarantees no overshoot on
power up or while enabled through the EN pin.
The amplifier also contains an active pull
down, so that when the load is removed
quickly the output voltage transient is
minimal; thus output deviation due to load
transient is small and fairly well matched when
connecting and disconnecting the load.
An accurate 1.250V bandgap reference is
bootstrapped to the output in fixed output
versions of 2.7V and higher. This increases
both the low frequency and high frequency
PSRR. The adjustable version also has the
bandgap reference bootstrapped to the output,
thus the lowest externally programmable
output voltage is 2.7V. The 2.5V fixed output
version has the bandgap always connected to
the Vin pin. Unlike many LDOs, the bandgap
reference is not brought out for filtering by the
user. This tradeoff was made to maintain good
PSRR at high frequency (PSRR can be
degraded in a system due to switching noise
coupling into this pin). Also, often leakages of
the bypass capacitor or other components
cause an error on this high impedance
bandgap node. Thus, this tradeoff has been
made with "ease of use" in mind.
© 2012 Exar Corporation
12/17
Rev. 2.1.0