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TC1070VCT Datasheet(PDF) 4 Page - TelCom Semiconductor, Inc |
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TC1070VCT Datasheet(HTML) 4 Page - TelCom Semiconductor, Inc |
4 / 12 page TC1070 4 50mA ADJUSTABLE CMOS LDO WITH SHUTDOWN PRELIMINARY INFORMATION TC1070-01 6/13/97 Output Capacitor A 1 µF (min) capacitor from VOUT to ground is recom- mended. The output capacitor should have an effective series resistance of 5 Ω or less, and a resonant frequency above 1MHz. A 1 µF capacitor should be connected from VIN 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 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: PD ≈ (VINMAX – VOUTMIN)ILOADMAX Where: PD = Worst case actual power dissipation VIN MAX = Maximum voltage on VIN VOUT MIN = Minimum regulator output voltage ILOAD MAX = Maximum output (load) current Equation 2. The maximum allowable 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. PD MAX = (TJMAX – TJMAX) θJA Where all terms are previously defined. Equation 3. 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, 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 0.05 µA (typical) and VOUT falls to zero volts. Adjust Input 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 VREF to (VIN – 0.05V). If so desired, a small capacitor (100pF to 0.01 µF) may be added to the ADJ input to further reduce output noise. Figure 1. 2.45 Battery-Operated Supply C2 1 µF C3 100pF 0.01 µF (Optional) Shutdown Control (from Power Control Logic) TC1070 VIN 1 2 3 4 R2 2.2M R1 2.2M +2.45V 5 VOUT ADJ SHDN GND 3.0V BATTERY C1 1 µF |
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