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TS317CMRN Datasheet(PDF) 6 Page - Taiwan Semiconductor Company, Ltd |
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TS317CMRN Datasheet(HTML) 6 Page - Taiwan Semiconductor Company, Ltd |
6 / 14 page TS317 3-Terminal Adjustable Positive Voltage Regulator 6/14 Version: D07 Application information Basic Circuit Operation The TS317 is a 3-terminal floating regulator. In operation, the TS317 develops and maintains a nominal 1.25V reference (Vref) between its output and adjustment terminals. This reference voltage is converted to a programming current (Iprog.) by R1 (see Figure 17), and this constant current flows through R2 to ground. The regulated output voltage is given by: Vout = Vref ( 1 + R2 / R1 ) + Iadj * R2 Since the current from the adjustment terminal (Iadj) represents an error term in the equation, the TS317 was designed to control Iadj to less than 100uA and keep it constant. To do this, all quiescent operating current is returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is less than this minimum, the output voltage will rise. Since the TS317 is a floating regulator, it is only the voltage differential across the circuit which is important to performance, and operation at high voltages with respect to ground is possible. Figure 17. Basic Circuit Configuration Figure 18. Voltage Regulator with Protection Diode Protection Diode When external capacitors are used with any I.C. regulator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. Figure 18 shows the TS317 with the recommended protection diodes for output voltages in excess of 25 V or high capacitance values (Co > 25uF, Cadj > 10uF). Diode D1 prevents Co from discharging thru the I.C. during an input short circuit. Diode D2 protects against capacitor CADJ discharging through the I.C. during an output short circuit. The combination of diodes D1 and D2 prevents CADJ from discharging through the I.C. during an input short circuit. Load Regulation The TS317 is capable of providing extremely good load regulation, but a few precautions are needed to obtain maximum performance. For best performance, the programming resistor (R1) should be connected as close to the regulator as possible to minimize line drops which effectively appear in series with the reference, thereby degrading regulation. The ground end of R2 can be returned near the load ground to provide remote ground sensing and improve load regulation. External Capacitor A 0.1 µF disc or 1µF tantalum input bypass capacitor (Cin) is recommended to reduce the sensitivity to input line impedance. The adjustment terminal may be bypassed to ground to improve ripple rejection. This capacitor (Cadj) prevents ripple from being amplified as the output voltage is rejection about 15dB at 120 HZ in a 10V application. Although the TS317 is stable with no output capacitance, like any feedback circuit, certain values of external capacitance can cause excessive ringing. An output increased. A 10u µF capacitor should improve ripple capacitance (Co) in the form of a 1uF tantalum or 25uF aluminum electrolytic capacitor on the output swamps this effect and insures stability. |
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