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SP317L Datasheet(PDF) 10 Page - Sipex Corporation |
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SP317L Datasheet(HTML) 10 Page - Sipex Corporation |
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10 / 13 page  0 Date: 8//06 Rev H SP37L 3-Terminal 00mA Adjustable Voltage Regulator © 2006 Sipex Corporation In operation, the SP37L develops a nominal .2V reference voltage, VREF, between the output and the adjustment terminal. The reference voltage is impressed across program resistor R and, since the voltage is constant, a constant current I then flows through the output set resistor R2, giving an output voltage of: Vout = Vref * { + R2/R} + Iadj(R2) Since the 100μA current from the adjust- ment terminal represents an error term, the SP37L was designed to minimize IADJ and make it very constant with line and load changes. To do this, all quiescent operating current is returned to the output establishing a minimum load current re- quirement. If there is insufficient load on the output, the output will rise. Figure 21: R1, R2 and Quiescent Current EXTERNAL CAPACITORS Although the SP37L is stable with no output capacitors, like any feedback circuit, certain values of external capacitance can APPLICATION INFORmATION cause excessive ringing. This occurs with values between 00pF and 000pF. A µF solid tantalum (or 2µF aluminum electrolytic) on the output swamps this effect and insures stability. An input bypass capacitor is recommended in case the regulator is more than 6 inches away from the usual large filter capacitor. A 0. µF disc or µF solid tantalum on the input is suitable input bypassing for almost all applications. The device is more sensitive to the absence of input bypassing when adjustment or output capacitors are used, but the above values will eliminate the possibility of problems. The adjustment terminal can be bypassed to ground on the SP37L to improve ripple rejection and noise. This bypass capacitor prevents ripple and noise from being amplified as the output voltage is increased. With a 0µF bypass capacitor 80dB ripple rejection is obtainable at any output level. Increases over 0µF do not appreciably improve the ripple rejection at frequencies above 20Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor fromdischargingthroughinternallowcurrent 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 2µF in aluminum electrolytic to equal µF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies; but some types have a large decrease in capacitance at frequencies around 0.MHz. For this reason, a 0.0µF disc may seem to work better than a 0.µF disc as a bypass. SP317L VIN R 2 R 1 ADJ I ADJ VOUT VIN VOUT VREF I1 |
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