TC1054 Datasheet, PDF (10/12 Pages) TelCom Semiconductor, Inc – 50mA CMOS LDO WITH SHUTDOWN AND ERROR OUTPUT

PRELIMINARY INFORMATION
100mA CMOS LDO WITH SHUTDOWN
AND ERROR OUTPUT
TC1055
DETAILED DESCRIPTION
The TC1055 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 TC1055 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
BATTERY
GND
TC1055VCT
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
V⁺
R1
1M
0.2µF
C2
BATTLOW
or RESET
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 by 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.
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:
TC1055-01 6/5/97
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