TC2054_09 Datasheet, PDF (11/22 Pages) Microchip Technology – 50 mA, 100 mA, and 150 mA CMOS LDOs with Shutdown and Error Output

4.0 DETAILED DESCRIPTION
The TC2054, TC2055 and TC2186 are precision fixed
output voltage regulators. (If an adjustable version is
desired, refer to the TC1070/TC1071/TC1187 data
sheet (DS21353). Unlike bipolar regulators, the
TC2054, TC2055 and TC2186 supply current does not
increase with load current. In addition, V_OUT remains
stable and within regulation over the entire 0 mA to
maximum output current operating load range.
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
1 µF
V_OUT
BATTERY
TC2054
GND _TC2055
TC2186
SHDN ERROR
Shutdown Control
(to CMOS Logic or Tie C2 Required Only
to V_IN if unused) if ERROR is used as a
Processor RESET Signal
(See Text)
V_OUT
1 µF
C₁
V+
R₁
1MΩ
BATTLOW
or RESET
0.2 µF
C₂
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 threshold is 5%
below rated V_OUT regardless of the programmed
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 when 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).
The ERROR pin sink current is self-limiting to
approximately 18 mA.
TC2054/2055/2186
V_OUT
V_TH
HYSTERESIS (V_HYS)
ERROR
V_IH
V_OL
FIGURE 4-2:
Error Output Operation.
4.2 Output Capacitor
A 1 µF (minimum) capacitor from V_OUT to ground is
required. The output capacitor should have an effective
series resistance of 0.01Ω. to 5Ω for V_OUT = 2.5V, and
0.05Ω. to 5Ω for V_OUT < 2.5V. Ceramic, tantalum and
aluminum electrolytic capacitors 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 Input Capacitor
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 this AC filter capacitor, or if a battery is
used as the power source. Aluminum electrolytic or
tantalum capacitors can be used (since many
aluminum electrolytic capacitors freeze at
approximately -30°C, solid tantalum 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.
© 2009 Microchip Technology Inc.
DS21663D-page 11