PRELIMINARY INFORMATION
50mA CMOS LDO WITH SHUTDOWN
AND ERROR OUTPUT
TC1054
DETAILED DESCRIPTION
The TC1054 is a precision fixed output voltage regula-
tor. (If an adjustable version is desired, please see the
TC1070 or TC1071 data sheets.) Unlike the bipolar regula-
tors, the TC1054 supply current does not increase with load
current. In addition, V
OUT
remains stable and within regula-
tion at very low load currents (an important consideration in
RTC and CMOS RAM battery back-up applications).
Figure 1 shows a typical application circuit. The regula-
tor 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) and V
OUT
falls to zero volts and ERROR is open
circuited.
Pull-up resistor R1 can be tied to V
OUT
, V
IN
or any other
voltage less than (V
IN
= 0.3V).
V
OUT
V
TH
HYSTERESIS (V
HYS
)
ERROR
V
IH
V
OL
Figure 2. ERROR Output Operation
Output Capacitor
V
IN
1µF
V
OUT
1µF
C1
GND
V
OUT
BATTERY
TC1054VCT
V
+
SHDN
Shutdown Control
(to CMOS Logic or Tie
to V
IN
if unused)
ERROR
R1
1M
BATTLOW
or RESET
C2 Requires Only
if ERROR is used as a
Processor RESET Signal
(See Text)
0.2µF
C2
Figure 1. Typical Application Circuit
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, and a resonant frequency
above 1MHz. 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 tanta-
lum 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 tech-
niques.
ERROR Open Drain 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
regardless of the programmed output voltage value
(e.g. ERROR = V
OL
at 4.75 (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
falls to V
TH
, and
inactive when V
OUT
rises above V
TH
= V
HYS
.
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 C2 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.
TC1054-01 6/12/97
Thermal Considerations
Thermal Shutdown
Integrated thermal protection circuitry shuts the regula-
tor off when die temperature exceeds 160°C. The regulator
remains off until the die temperature drops to approximately
150°C.
Power Dissipation
The amount of power the regulator dissipates is prima-
rily a function of input and output voltage, and output current.
The following equation is used to calculate worst case
actual
power dissipation:
4
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
