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ICL7660AIBAZA-T Datasheet(PDF) 10 Page - Intersil Corporation |
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ICL7660AIBAZA-T Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 12 page 10 FN3072.7 October 10, 2005 Positive Voltage Doubling The ICL7660 and ICL7660A may be employed to achieve positive voltage doubling using the circuit shown in Figure 19. In this application, the pump inverter switches of the ICL7660 and ICL7660A are used to charge C1 to a voltage level of V+ -VF (where V+ is the supply voltage and VF is the forward voltage drop of diode D1). On the transfer cycle, the voltage on C1 plus the supply voltage (V+) is applied through diode D2 to capacitor C2. The voltage thus created on C2 becomes (2V+) - (2VF) or twice the supply voltage minus the combined forward voltage drops of diodes D1 and D2. The source impedance of the output (VOUT) will depend on the output current, but for V+ = 5V and an output current of 10mA it will be approximately 60 Ω. Combined Negative Voltage Conversion and Positive Supply Doubling Figure 20 combines the functions shown in Figures 13 and Figure 19 to provide negative voltage conversion and positive voltage doubling simultaneously. This approach would be, for example, suitable for generating +9V and -5V from an existing +5V supply. In this instance capacitors C1 and C3 perform the pump and reservoir functions respectively for the generation of the negative voltage, while capacitors C2 and C4 are pump and reservoir respectively for the doubled positive voltage. There is a penalty in this configuration which combines both functions, however, in that the source impedances of the generated supplies will be somewhat higher due to the finite impedance of the common charge pump driver at pin 2 of the device. Voltage Splitting The bidirectional characteristics can also be used to split a higher supply in half, as shown in Figure 21. The combined load will be evenly shared between the two sides. Because the switches share the load in parallel, the output impedance is much lower than in the standard circuits, and higher currents can be drawn from the device. By using this circuit, and then the circuit of Figure 16, +15V can be converted (via +7.5, and -7.5) to a nominal -15V, although with rather high series output resistance ( ~250Ω). Regulated Negative Voltage Supply In some cases, the output impedance of the ICL7660 and ICL7660A can be a problem, particularly if the load current varies substantially. The circuit of Figure 22 can be used to overcome this by controlling the input voltage, via an ICL7611 low-power CMOS op amp, in such a way as to maintain a nearly constant output voltage. Direct feedback is inadvisable, since the ICL7660s and ICL7660As output does not respond instantaneously to change in input, but only after the switching delay. The circuit shown supplies enough delay to accommodate the ICL7660 and ICL7660A, while maintaining adequate feedback. An increase in pump and storage capacitors is desirable, and the values shown provides an output impedance of less than 5 Ω to a load of 10mA. 1 2 3 4 8 7 6 5 + - VOUT V+ + - C2 C1 COSC ICL7660 ICL7660A FIGURE 18. LOWERING OSCILLATOR FREQUENCY 1 2 3 4 8 7 6 5 V + D2 C1 C2 VOUT = (2V+) - (2VF) + - + - D1 ICL7660 ICL7660A FIGURE 19. POSITIVE VOLT DOUBLER 1 2 3 4 8 7 6 5 V + D1 D2 C4 VOUT = (2V+) - (VFD1) - (VFD2) + - C2 + - C3 + - VOUT = - (nVIN - VFDX) C1 + - ICL7660 ICL7660A FIGURE 20. COMBINED NEGATIVE VOLTAGE CONVERTER AND POSITIVE DOUBLER 1 2 3 4 8 7 6 5 + - + - 50 µF 50 µF + - 50 µF RL1 VOUT = V+ - V- 2 V+ V - RL2 ICL7660 ICL7660A FIGURE 21. SPLITTING A SUPPLY IN HALF ICL7660, ICL7660A |
Similar Part No. - ICL7660AIBAZA-T |
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