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TC1187 Datasheet(PDF) 5 Page - Microchip Technology |
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TC1187 Datasheet(HTML) 5 Page - Microchip Technology |
5 / 16 page © 2002 Microchip Technology Inc. DS21353B-page 5 TC1070/TC1071/TC1187 3.0 DETAILED DESCRIPTION The TC1070, TC1071 and TC1187 are adjustable fixed 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, VOUT remains stable and within regulation over the entire 0mA to IOUTMAX 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 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), VOUT falls to zero volts. FIGURE 3-1: BATTERY-OPERATED SUPPLY 3.1 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: The voltage adjustment range of the TC1070, TC1071 and TC1187 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. 3.2 Output Capacitor A1 µF (min) capacitor from VOUT to ground is recommended. The output capacitor should have an effective series resistance greater than 0.1 Ω and less than 5.0 Ω, 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 capacitor types can be used. (Since many aluminum electrolytic capacitors freeze at approxi- mately -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. TC1070 TC1071 TC1187 VOUT SHDN GND C2 1 µF + VIN +2.45V Shutdown Control (from Power Control Logic) C1 1 µF + 3.0V Battery + C3 100pF to 0.01 µF (Optional) R1 470K 1 5 2 4 3 ADJ R2 470K VOUT =VREF x [ +1 ] R1 R2 |
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