TC1072 Datasheet, PDF (4/12 Pages) TelCom Semiconductor, Inc – 50mA CMOS LDO WITH SHUTDOWN, ERROR OUTPUT AND VREF BYPASS

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
BATTERY
GND
Bypass
TC1072
SHDN
ERROR
Shutdown Control
(to CMOS Logic or Tie
to V_IN if unused)
C2 Requires Only
if ERROR is used as a
Processor RESET Signal
(See Text)
V_OUT
1µF
C1
C3, 470pF
V⁺
R1
1M
BATTLOW
or RESET
0.2µF
C2
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.
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).
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.
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.
TC1072-01 6/16/97
4