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TS317L Datasheet(PDF) 3 Page - Taiwan Semiconductor Company, Ltd |
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TS317L Datasheet(HTML) 3 Page - Taiwan Semiconductor Company, Ltd |
3 / 6 page Application Information Basic Circuit Operation The TS317L is a 3-terminal floating regulator. In operation, the TS317L 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 TS317L 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 TS317L 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 1. basic circuit configuration Load Regulation The TS317L is capable of providing extremely good load regulation, but a few precautions are needed to obtain maximum performance. The current set resistor connected between the adjustment therminal and the output terminal (usually 240Ω) should be tied directly to the output of the regulator rather than near the load. This eliminates line drops from appearing effectively in series with the reference and degrading regulation. For example, a 15V regulator with 0.05Ω resistance between the regulator and load will have a load regulation due to line resistance of 0.05Ω x Io. If the set resistor is connected near the load the effective line resistance will be 0.05Ω (1+ R2/R1) or in this case, 11.5 times worse. Figure 6 shows the effect of resistance between the regulator and 240Ω set resistor. With the TO-92 package, it is easy to minimize the resistance from the case of the set resistor, by using two separate leads to the output pin. The ground of R2 can be returned near the ground of the load to provide remote ground sensing and improve load regulation. Figure 2. Regulator with line resistance in output lead External Capacitor An input bypass capacitor is recommended in case the regulator is more than 6 inches away from the usual large filter 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 and noice. This capacitor (Cadj) prevents ripple from being amplified as the output voltage is increased. With a 10uF bypass capacitor 80dB ripple rejection is obtainable at any output level. Increased over 10uF do not appreciably improve the ripple rejection at frequencies above 120Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device. In general, the best type of capacitors to use is solid tantalum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25uF in aluminum electrolytic to equal 1uF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies; but some types have a large TS317L 3-6 2003/12 rev. A |
Similar Part No. - TS317L |
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Similar Description - TS317L |
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