TC1070_07 Datasheet, PDF (10/20 Pages) Microchip Technology – 50mA, 100mA and 150mA Adjustable CMOS LDOs with Shutdown

TC1070/TC1071/TC1187
4.0 DETAILED DESCRIPTION
The TC1070, TC1071 and TC1187 are adjustable
output voltage regulators. (If a fixed version is desired,
please see the TC1014/TC1015/TC1185 data sheet.)
Unlike bipolar regulators, the TC1070, TC1071 and
TC1187 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 operating
load current range, (an important consideration in RTC
and CMOS RAM battery back-up applications).
Figure 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.
3.0V ⁺
Battery
1
+ _C1
V_IN
V_OUT
1 μF TC1070
TC1071
TC1187
2
GND
5
C2 ⁺
1 μF
+2.45V
R1
470K
3
SHDN
Shutdown Control
(from Power
Control Logic)
4
ADJ
C3
100 pF
to 0.01 μF
(Optional)
R2
470K
FIGURE 4-1:
Battery-Operated Supply
4.1 Adjust Input
The output voltage setting is determined by the values
of R₁ and R₂ (Equation 4-1). 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 4-1:
[ ] V_OUT = V_REF x
R1
R2
+
1
The voltage adjustment range of the TC1070, TC1071
and TC1187 is from V_REF to (V_IN – 0.05V). If so desired,
a small capacitor (10 pF to 0.01 μF) may be added to
the ADJ input to further reduce output noise.
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 recom-
mended 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.
DS21353D-page 10
© 2007 Microchip Technology Inc.