TC1070 Datasheet, PDF (4/12 Pages) TelCom Semiconductor, Inc – 50mA ADJUSTABLE CMOS LDO WITH SHUTDOWN

PRELIMINARY INFORMATION
50mA ADJUSTABLE CMOS
LDO WITH SHUTDOWN
TC1070
DETAILED DESCRIPTION
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, V_OUT 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 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) and V_OUT falls to zero volts.
Output Capacitor
A 1µF (min) capacitor from V_OUT to ground is recom-
mended. The output capacitor should have an effective
series resistance of 5Ω or less, and a resonant frequency
above 1MHz. 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 capaci-
tor 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.
Thermal Considerations
3.0V
BATTERY
1 _VIN
C1
1µF
V_OUT ⁵
C2
1µF
2
GND _TC1070
+2.45V
R1
2.2M
3
SHDN
ADJ ⁴
Thermal Shutdown
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.
Power Dissipation
The amount of power the regulator dissipates is prima-
rily a function of input and output voltage, and output current.
The following equation is used to calculate worst case
actual power dissipation:
Shutdown Control
(from Power Control Logic)
C3
100pF
0.01µF
(Optional)
R2
2.2M
Figure 1. 2.45 Battery-Operated Supply
Adjust Input
P_{D ≈} (V_{INMAX –} V_{OUTMIN)ILOADMAX}
Where:
P_D = Worst case actual power dissipation
V_INMAX = Maximum voltage on V_IN
V_OUTMIN = Minimum regulator output voltage
I_LOADMAX = Maximum output (load) current
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.
The output voltage setting is calculated using the follow-
ing equation.
[ ] ^{VOUT = VREF x}
R1 _{+ 1}
R2
Equation 1.
The voltage adjustment range of the TC1070 is from
V_REF to (V_IN – 0.05V). If so desired, a small capacitor (100pF
to 0.01µF) may be added to the ADJ input to further reduce
output noise.
Equation 2.
The maximum allowable power dissipation (Equation 2)
is a function of the maximum ambient temperature (T_AMAX),
the maximum allowable die temperature (125°C) and the
thermal resistance from junction-to-air (θ_JA). SOT-23A-5
packag has a θ_JA of approximately 220°C/Watt when
mounted on a single layer FR4 dielectric copper clad PC
board.
P_{D MAX =} (T_JMAX – T_JMAX)
θ_JA
Where all terms are previously defined.
Equation 3.
TC1070-01 6/13/97
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