PRELIMINARY INFORMATION
50mA ADJUSTABLE CMOS
LDO WITH SHUTDOWN
TC1070
DETAILED DESCRIPTION
Output Capacitor
The TC1070 is a precision fixed output voltage regula-
tor. (If a fixed version is desired, please see the TC1014 or
TC1015 data sheets.) Unlike the bipolar regulators, the
TC1070 supply current does not increase with load current.
In addition, VOUT remains stable and within regulation 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 VIH, and shutdown (disabled) when SHDN is at or
below VIL. 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 VOUT falls to zero volts.
A 1µF (min) capacitor from VOUT to ground is recom-
mended. The output capacitor should have an effective
series resistance of 5Ω or less, and a resonant frequency
above1MHz.A1µFcapacitorshouldbeconnected fromVIN
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
thepowersource. Aluminumelectrolyticortantalumcapaci-
tor types can be used. (Since many aluminum electrolytic
capacitors freeze at approximately – 30°C, solid tantalums
arerecommendedforapplicationsoperatingbelow –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.
Thermal Considerations
Thermal Shutdown
1
5
V
V
OUT
+2.45V
IN
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.
C1
1µF
C2
1µF
3.0V
BATTERY
2
GND
TC1070
R1
Power Dissipation
2.2M
The amount of power the regulator dissipates is prima-
rilyafunctionofinputandoutputvoltage,andoutputcurrent.
The following equation is used to calculate worst case
actual power dissipation:
3
4
ADJ
C3
100pF
0.01µF
SHDN
R2
2.2M
PD ≈ (VIN
VOUT
ILOAD
)
MIN MAX
–
MAX
(Optional)
Where:
Shutdown Control
(from Power Control Logic)
PD = Worst case actual power dissipation
= Maximum voltage on VIN
VIN
VOUT
MAX
Figure 1. 2.45 Battery-Operated Supply
= Minimum regulator output voltage
MIN
ILOADMAX = Maximum output (load) current
Adjust Input
Equation 2.
The output voltage setting is determined by the values
of R1 and R2 (Figure 1). The ohmic values of these resistors
should be between 470K and 3M to minimize bleeder
current.
Theoutputvoltagesettingiscalculatedusingthefollow-
ing equation.
The maximumallowable power dissipation (Equation 2)
is a function of the maximum ambient temperature (TAMAX),
the maximum allowable die temperature (125°C) and the
thermal resistance from junction-to-air (θJA). SOT-23A-5
packag has a θJA of approximately 220°C/Watt when
mounted on a single layer FR4 dielectric copper clad PC
board.
R1
VOUT = VREF
x
+ 1
[R2 ]
Equation 1.
PD MAX (TJMAX – TJ
)
=
MAX
θJA
The voltage adjustment range of the TC1070 is from
VREF to (VIN – 0.05V). If so desired, a small capacitor (100pF
to 0.01µF) may be added to the ADJ input to further reduce
output noise.
Where all terms are previously defined.
Equation 3.
4
TC1070-01 6/13/97
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
