PRELIMINARY INFORMATION
50mA CMOS LDO WITH SHUTDOWN,
ERROR OUTPUT AND V
REF
BYPASS
TC1072
DETAILED DESCRIPTION
The TC1072 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 TC1072 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.
V
IN
1µF
V
OUT
V
OUT
1µF
C1
GND
Bypass
V
OUT
V
TH
HYSTERESIS (V
HYS
)
ERROR
V
IH
V
OL
Figure 2. ERROR Output Operation
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, 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 tantalum capaci-
tor 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.
BATTERY
TC1072
V
+
SHDN
Shutdown Control
(to CMOS Logic or Tie
to V
IN
if unused)
ERROR
R1
1M
C3, 470pF
C2 Requires Only
if ERROR is used as a
Processor RESET Signal
(See Text)
0.2µF
C2
BATTLOW
or RESET
Bypass Input
Figure 1. Typical Application Circuit
ERROR Open Drain Output
ERROR is driven low whenenver V
OUT
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 = V
OL
at 4.75 (typ) for a 5.0V regulator and 2.85 (typ)
for a 3.0V regulator). ERROR ouput 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.
Pull-up resistor R1 can be tied to V
OUT
, V
IN
or any other
voltage less than (V
IN
+0.3V).
TC1072-01
6/16/97
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.
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.
4
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