TC1269_13 Datasheet, PDF (4/12 Pages) Microchip Technology – 300mA CMOS LDO with Shutdown and VREF Bypass

TC1269
3.0 DETAILED DESCRIPTION
The TC1269 is a precision regulator available in fixed
voltages. Unlike the bipolar regulators, the TC1269
supply current does not increase with load current. In
addition, V_OUT remains stable and within regulation
over the entire 0mA to I_OUTMAX operating load current
range, (an important consideration in RTC and CMOS
RAM battery backup applications).
Figure 3-1 shows a typical application circuit. The
regulator is enabled any time the shutdown input
(SHDN) is at or above V_IH, and shutdown (disabled)
when SHDN is at or below V_IL. SHDN may be
controlled by a CMOS logic gate, or I/O port of a
microcontroller. If the SHDN input is not required, it
should be connected directly to the input supply. While
in shutdown, supply current decreases to 0.05A
(typical), V_OUT falls to zero.
FIGURE 3-1:
TYPICAL APPLICATION
CIRCUIT
V_OUT
1
+ _C1 ^VOUT
1µF
2
NC
V_IN ⁸
7
SHDN
TC1269
3 _NC
6
NC
4 _{GND Bypass}
+ _C1
1µF
Battery +
Shutdown Control
(from Power
–
Control Logic)
C_BYPASS
470pF
(Optional)
3.1 Bypass Input
A 470pF capacitor connected from the Bypass input to
ground reduces noise present on the internal
reference, which in turn significantly reduces output
noise. If output noise is not a concern, this input may be
left unconnected. Larger capacitor values may be
used, but results in a longer time period to rated output
voltage when power is initially applied.
3.2 Output Capacitor
A 1F (min) capacitor from V_OUT to ground is
recommended. The output capacitor should have an
effective series resistance greater than 0.1 and less
than 5.0, and a resonant frequency above 1MHz. A
1F capacitor should be connected from V_IN to GND if
there is more than 10 inches of wire between the
regulator and the AC filter capacitor, or if a battery is
used as the power source. Aluminum electrolytic or
tantalum capacitor types can be used. (Since many
aluminum electrolytic capacitors freeze at approxi-
mately -30°C, solid tantalums are recommended for
applications operating below -25°C.) When operating
from sources other than batteries, supply-noise
rejection and transient response can be improved by
increasing the value of the input and output capacitors
and employing passive filtering techniques.
DS21380C-page 4
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