PRELIMINARY INFORMATION
100mA CMOS LDO WITH SHUTDOWN,
ERROR OUTPUT AND VREF BYPASS
TC1073
DETAILED DESCRIPTION
The TC1073 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 TC1073 supply current does not increase with load
current. In addition, VOUT 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 VIH, and shutdown (disabled) when SHDN is at or
below VIL. 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 VOUT falls to zero volts and ERROR is open-
circuited.
VOUT
HYSTERESIS (VHYS
)
VTH
ERROR
VIH
VOL
Figure 2. ERROR Output Operation
Output Capacitor
A 1µF (min) capacitor from VOUT to ground is recom-
mended. The output capacitor should have an effective
series resistance of 5Ω or less, and a resonant frequency
above1MHz.A1µFcapacitorshouldbeconnected fromVIN
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
thepowersource. Aluminumelectrolyticortantalumcapaci-
tor types can be used. (Since many aluminum electrolytic
capacitors freeze at approximately – 30°C, solid tantalums
arerecommendedforapplicationsoperatingbelow –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.
V
V
V
OUT
OUT
IN
1µF
1µF
C1
BATTERY
Bypass
TC1073
GND
C3, 470pF
+
V
SHDN
ERROR
R1
1M
Shutdown Control
(to CMOS Logic or Tie
C2 Requires Only
if ERROR is used as a
Processor RESET Signal
(See Text)
BATTLOW
or RESET
to V if unused)
IN
0.2µF
C2
Bypass Input
Figure 1. Typical Application Circuit
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.
ERROR Open Drain Output
ERROR is driven low whenenver VOUT falls out of
regulation by more than – 5% (typical). The condition my be
caused by low input voltage, output current limiting, or
thermal limiting. The ERROR output voltage value (e.g.
ERROR=VOL at4.75(typ)fora5.0Vregulatorand2.85(typ)
for a 3.0V regulator). ERROR ouput operation is shown in
Figure 2.
Thermal Considerations
Thermal Shutdown
Note that ERROR is active when VOUT falls to VTH, and
inactive when VOUT rises above VTH = VHYS.
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.
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 VIH 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 VOUT, VIN or any other
voltage less than (VIN +0.3V).
Power Dissipation
The amount of power the regulator dissipates is prima-
rilyafunctionofinputandoutputvoltage,andoutputcurrent.
4
TC1073-01 6/5/97
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
