TC1173 Datasheet, PDF (4/12 Pages) TelCom Semiconductor, Inc – 300mA CMOS LDO with Shutdown, ERROR Output and Bypass

TC1173
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 0.05µA
(typical), V_OUT falls to zero and ERROR is disabled.
FIGURE 3-1:
TYPICAL APPLICATION
CIRCUIT
V_OUT
1
+ _C1
V_OUT
1µF
2
GND
8
V_IN
7
NC
TC1173
R3
1M
3
NC
6
SHDN
+ _C2
1µF
+
Battery ^–
4
5
Bypass ERROR
RESET or
Battery Low
Shutdown Control
(from Power Control Logic)
C3
0.2µF
C_BYPASS
470pF
(Optional)
C3 required only if ERROR
is used as a processor RESET signal.
(see text)
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:
V_OUT
V_TH
ERROR OUTPUT
OPERATION
HYSTERESIS (V_H)
ERROR
V_IH
V_OL
3.2 Output Capacitor
A 1µF (min) capacitor from V_OUT to ground is
recommended. The output capacitor should have an
effective series resistance greater than 0.1Ω and less
than 5.0Ω. A 1µF 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.
DS21362B-page 4
© 2002 Microchip Technology Inc.