TS5205_1 Datasheet, PDF (4/6 Pages) Taiwan Semiconductor Company, Ltd – 150mA Low Noise LDO Voltage Regulator with Enable

Application Information
Enable Input
TS5205 series feature an active-high (>2V) enable (EN)
input that allows ON/OFF control of the regulator.
Current drain reduces to “zero” when the device is
shutdown, with only micro-amperes of leakage current.
The EN is compatible with CMOS logic interfacing. EN
may be directly tied to Vin and pulled up to the
maximum supply voltage.
Input Capacitor Requirement
An input capacitor of 1uF or greater is recommended
when the device is more than 10” away from the bulk
AC supply capacitance or when the supply is a battery.
Reference Bypass Capacitor
Bypass is connected to the internal voltage reference. A
470uF capacitor (Cbypass) connected from Bypass to
Ground quiets this reference, providing a significant
reduction in output noise. Cbypass reduces the
regulator phase margin; when using Cbypass, output
capacitors of 2.2uF or greater are generally required to
maintain stability.
The star up speed of the TS5205 is inversely
proportional to the size of the reference bypass
capacitor. Applications requiring a slow ramp up of
output voltage should consider larger values of
Cbypass. Likewise, if rapid turn on is necessary,
consider omitting Cbypass. If output noise is not a
major concern, omitted Cbypass and leave Bypass
open.
Output Capacitor Requirement
The TS5205 series requires an output capacitor to
maintain stability and improve transient response is
necessary. The value of this capacitor is dependent
upon whether a reference bypass capacitor is used.
1uF minimum is recommended when Cbypass is not
used. 2.2uF minimum is recommended when Cbypass
is 470uF. Larger values improve the regulator’s
transient response. The output capacitor value may be
increased without limit.
The output capacitor should have an ESR (effective
series resistance) less than 5Ω and a resonant
frequency above 1MHz. Ultra low ESR capacitors can
cause a low amplitude oscillation on the output and/or
under damped transient response.
Most of tantalum or aluminum electrolytic capacitors
are adequate; film types will work. Since many
aluminum electrolytic have electrolytes that freeze at
about –30^oC, solid tantalums are recommended for
operation below –25^oC. At lower values of output
current, less output capacitance is required for output
stability. The capacitor can be reduced to 0.47uF for
current below 10mA or 0.33uF for currents below 1mA.
No Load Stability
The TS5205 series iwill remain stable and in regulation
with no load, unlike many other voltage regulators.
This is especially important in CMOS RAM keep alive
applications.
Adjustable Regulator Design
The adjustable regulator versions can be adjusted to a
specific output voltage by using two external resistors
to programming the output voltage anywhere between
1.25 and the 16V maximum operating rating of the
family.
Two resistors are used. Resistors can be quite large
up to 470kΩ, because of the very high input
impedance and low bias current of the sense
comparator, the resistor values are calculated by:
Vout = 1.242V * (R2 / R1 + 1)
A capacitor from Adj to Ground provides greatly
improved noise performance.
Dual Supply Operation
When used in dual supply systems where the regulator
load is returned to a negative supply, the output
voltage must be diode clamped to ground.
TS5205 series
4-6
2004/09 rev. B