TC1173
DS21362C-page 4 2002-2012 Microchip Technology Inc.
3.0 DETAILED DESCRIPTION
The TC1173 is a fixed output, low drop-out regulator.
Unlike bipolar regulators, the TC1173’s 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 back-up 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 and ERROR is disabled.
FIGURE 3-1: TYPICAL APPLICATION
CIRCUIT
3.1 ERROR Output
ERROR is driven low whenever V
OUT
falls out of
regulation by more than – 5% (typical). This condition
may be caused by low input voltage, output current
limiting, or thermal limiting. The ERROR
threshold is
5% below rated V
OUT
regardless of the programmed
output voltage value (e.g., ERROR
= V
OL
at 4.75V
(typ.) for a 5.0V regulator and 2.85V (typ.) for a 3.0V
regulator). ERROR output operation is shown in
Figure 3-2.
Note that ERROR
is active when V
OUT
is at or below
V
TH
, and inactive when V
OUT
is above V
TH
+ V
H
.
As shown in Figure 3-1, ERROR
can be used as a
battery low flag, or as a processor RESET
signal (with
the addition of timing capacitor C3). R1 x C3 should be
chosen to maintain ERROR
below V
IH
of the processor
RESET
input for at least 200 msec to allow time for the
system to stabilize. Pull-up resistor R1 can be tied to
V
OUT
, V
IN
or any other voltage less than (V
IN
+ 0.3V).
FIGURE 3-2: ERROR OUTPUT
OPERATION
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. 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
approximately -30°C, solid tantalums are recom-
mended 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.
3.3 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.
TC1173
1
2
3
4
V
OUT
V
OUT
C
BYPASS
470pF
(Optional)
Shutdown Control
(from Power Control Logic)
C1
1μF
GND
NC
Bypass
V
IN
NC
SHDN
+
ERROR
5
6
7
8
C3 required only if ERROR
is used as a processor RESET signal.
(see text)
Battery
RESET or
Battery Low
R3
1M
C2
1μF
C3
0.2μF
+
+
–
V
TH
V
OUT
ERROR
V
IH
V
OL
HYSTERESIS (V
H
)
