TC1269
DS21380C-page 4 2002-2012 Microchip Technology Inc.
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 0.05A
(typical), V
OUT
falls to zero.
FIGURE 3-1: TYPICAL APPLICATION
CIRCUIT
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 1F (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
1F 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.
TC1269
1
2
3
4
6
7
8
NC
NC
GND
Bypass
NC
SHDN
Battery
V
OUT
V
OUT
C
BYPASS
470pF
(Optional)
Shutdown Control
(from Power
Control Logic)
C1
1µF
V
IN
+
C1
1µF
+
+
–
