TC1072_07 Datasheet, PDF (12/22 Pages) Microchip Technology – 50mA and 100mA CMOS LDOs with Shutdown, ERROR Output and VREF Bypass

TC1072/TC1073
4.0 DETAILED DESCRIPTION
The TC1072 and TC1073 are precision fixed output
voltage regulators. (If an adjustable version is desired,
please see the TC1070/TC1071/TC1187 data sheet.)
Unlike bipolar regulators, the TC1072 and TC1073’s
supply current does not increase with load current. In
addition, V_OUT remains stable and within regulation
over the entire 0 mA to I_OUTMAX load current range, (an
important consideration in RTC and CMOS RAM
battery back-up applications).
Figure 4-1 shows a typical application circuit. The
regulator 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 0.05 µA
(typical), V_OUT falls to zero volts, and ERROR is open-
circuited.
+
V_IN
V_OUT
1 μF
+
TC1072
TC1073
Battery
GND
Bypass
V_OUT
+
1 μF
C1
C3, 470 pF
Shutdown Control
(to CMOS Logic or Tie
to V_IN if unused)
SHDN ERROR
C2 Required Only
if ERROR is used as a
Processor RESET Signal
(See Text)
V+
R1
1M
0.2 μF
C2
BATTLOW
or RESET
FIGURE 4-1:
Typical Application Circuit.
4.1 ERROR Open-Drain Output
ERROR is driven low whenever V_OUT falls out of
regulation by more than –5% (typical). This condition
may be caused by low input voltage, output current
limiting, or thermal limiting. The ERROR output voltage
value (e.g. ERROR = V_OL at 4.75V (typical) for a 5.0V
regulator and 2.85V (typical) for a 3.0V regulator).
ERROR output operation is shown in Figure 4-2.
Note that ERROR is active tDELAY (typically, 2.5 µs)
after V_OUT falls to V_TH, and inactive when V_OUT rises
above V_TH by V_HYS.
As shown in Figure 4-1, 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 200 ms 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).
V_OUT
V_TH
HYSTERESIS (V_H)
ERROR
V_IH
V_OL
t_DELAY
FIGURE 4-2:
Error Output Operation.
4.2 Output Capacitor
A 1 µF (minimum) capacitor from V_OUT to ground is
recommended. The output capacitor should have an
effective series resistance greater than 0.1Ω and less
than 5.0Ω, and a resonant frequency above 1 MHz. A
1 µF 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 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
techniques.
4.3 Bypass Input
A 470 pF 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.
DS21354D-page 12
© 2007 Microchip Technology Inc.