TC1174 Datasheet, PDF (4/12 Pages) Microchip Technology – 300mA CMOS LDO with Shutdown and VREF Bypass

TC1174
3.0 DETAILED DESCRIPTION
The TC1174 is an adjustable low drop-out regulator.
Unlike bipolar regulators, the TC1174’s supply current
does not increase with load current. In addition, V_OUT
remains stable and within regulation over the entire
0mA to I_OUTMAX operating load current range, (an
important consideration in RTC and CMOS RAM
battery back-up applications).
Figure 3-1 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 0.05µA
(typical), V_OUT falls to zero.
FIGURE 3-1:
TYPICAL APPLICATION
CIRCUIT
V_OUT
+ _C1
1
V_OUT
1µF
8
V_IN
+ _C2
1µF
R1
470K
R2
2
GND
7
NC
TC1174
+
Battery
3
NC
6
SHDN
Shutdown
–
Control
(from Power
4 _ADJ
Bypass ^{5 Control Logic)}
470K
C_BYPASS
470pF
(Optional)
3.1 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.
3.2 Output Capacitor
A 1µF (min) capacitor from V_OUT to ground is required.
The output capacitor should have an effective series
resistance greater than 0.1Ω and less than 5.0Ω. 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
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.
3.3 Adjust Input
The output voltage setting is determined by the values
of R1 and R2 (Figure 3-1). The ohmic values of these
resistors should be between 470K and 3M to minimize
bleeder current.
The output voltage setting is calculated using the
following equation.
EQUATION 3-1:
[ ] V_OUT = V_REF x
R1
R2
+1
The voltage adjustment range of the TC1174 is from
V_REF to (V_IN – 0.05V).
DS21363B-page 4
© 2002 Microchip Technology Inc.