300mA CMOS LDO With Shutdown,
ERROR Output, And Bypass
TC1173
DETAILED DESCRIPTION
The TC1173 is a fixed output, low drop-out regulator.
Unlike bipolar regulators, the TC1173 supply current does not
increase with load current. In addition, V
OUT
remains stable and
within regulation at very low load currents (an important consid-
eration in RTC and CMOS RAM battery back-up applications).
TC1173 pin functions are detailed below:
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.
ERROR Output
ERROR is driven low whenever V
OUT
falls out of regu-
lation 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
regard-
less 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 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 1, ERROR can be used as a battery
low flag, or as a processor RESET signal (with the addition
of timing capacitor C2). R1 x C3 should be chosen to
maintain ERROR below V
IH
of the processor RESET input
for at least 200msec 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.)
V
OUT
PIN DESCRIPTIONS
Pin
No.
1
2
3
4
5
Symbol
V
OUT
GND
NC
Bypass
ERROR
Description
Regulated voltage output
Ground terminal
No connect
Reference bypass input. Connecting a 470pF
to this input further reduces output noise.
Out-of-Regulation Flag (Open Drain Out-
put). This output goes low when V
OUT
is out-
of-tolerance by approximately -5%.
Shutdown control input. The regulator is fully
enabled when a logic high is applied to this
input. The regulator enters shutdown when a
logic low is applied to this input. During
shutdown, output voltage falls to zero and
supply current is reduced to 0.05µA (typical).
No connect
Unregulated supply input
6
SHDN
7
8
NC
V
IN
V
TH
Hysteresis (V
H
)
Figure 1 shows a typical application circuit. The regula-
tor is enabled any time the shutdown input (SHDN) is above
V
IH
, and shutdown (disabled) when SHDN is at or below V
IL
.
ERROR
V
IH
V
OL
V
OUT
1
C1
1µF
2
V
OUT
V
IN
8
Figure 2: ERROR Output Operation
V
IN
GND
NC
7
R3
1M
TC1173
3
NC
SHDN
6
4
Bypass
ERROR
5
ERROR
C
BYPASS
470pF
(Optional)
Shutdown Control
(from Power Control Logic)
Output Capacitor
A 1µF (min) capacitor from V
OUT
to ground is recom-
mended. The output capacitor should have an effective
series resistance of 5Ω or less. 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 electro-
lytic or tantalum capacitor types can be used. (Since many
aluminum electrolytic capacitors freeze at approximately –
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.
3
Figure 1: Typical Application Circuit
TC1173-2 2/2/00
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
