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LT1054Y Datasheet(PDF) 9 Page - Texas Instruments |
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LT1054Y Datasheet(HTML) 9 Page - Texas Instruments |
9 / 27 page LT1054 SWITCHEDCAPACITOR VOLTAGE CONVERTERS WITH REGULATORS SLVS033F − FEBRUARY 1990 − REVISED NOVEMBER 2004 9 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 PRINCIPLES OF OPERATION Supply voltage VCC alternately charges CIN to the input voltage when CIN is switched in parallel with the input supply and then transfers charge to COUT when CIN is switched in parallel with COUT. Switching occurs at the oscillator frequency. During the time that CIN is charging, the peak supply current is approximately 2.2 times the output current. During the time that CIN is delivering a charge to COUT, the supply current drops to approximately 0.2 times the output current. An input supply bypass capacitor supplies part of the peak input current drawn by the LT1054 and averages the current drawn from the supply. A minimum input-supply bypass capacitor of 2 µF, preferably tantalum or some other low equivalent-series-resistance (ESR) type, is recommended. A larger capacitor is desirable in some cases. An example of this would be when the actual input supply is connected to the LT1054 through long leads or when the pulse currents drawn by the LT1054 might affect other circuits through supply coupling. In addition to being the output terminal, VOUT is tied to the substrate of the device. Special care must be taken in LT1054 circuits to avoid making VOUT positive with respect to any of the other terminals. For circuits with the output load connected from VCC to VOUT or from some external positive supply voltage to VOUT, an external transistor must be added (see Figure 14). This transistor prevents VOUT from being pulled above GND during startup. Any small general-purpose transistor such as a 2N2222 or a 2N2219 device can be used. Resistor R1 should be chosen to provide enough base drive to the external transistor so that it is saturated under nominal output voltage and maximum output current conditions. R1 v V OUT b I OUT R1 CIN Load VOUT VREF OSC VCC CAP− GND CAP+ FB/SD VIN VOUT COUT Pin numbers shown are for the P package. + + 1 2 3 4 LT1054 8 7 6 5 Figure 14. Circuit With Load Connected from VCC to VOUT (4) |
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