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ICL7662CPAZ Datasheet(PDF) 10 Page - Intersil Corporation |
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ICL7662CPAZ Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 10 page 10 Combined Negative Voltage Conversion and Posi- tive Supply Doubling Figure 23 combines the functions shown in Figure 16 and Figure 22 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 24. The combined load will be evenly shared between the two sides and, a high value resistor to the LV pin ensures start-up. 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 19, +30V can be converted (via +15V, and -15V) to a nominal -30V, although with rather high series output resistance (~250 Ω). Regulated Negative Voltage Supply In some cases, the output impedance of the ICL7662 can be a problem, particularly if the load current varies substantially. The circuit of Figure 25 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 ICL7662s output does not respond instantaneously to a change in input, but only after the switching delay. The circuit shown supplies enough delay to accommodate the ICL7662, 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. Other Applications Further information on the operation and use of the ICL7662 may be found in AN051 “Principles and Applications of the ICL7660 CMOS Voltage Converter”. 1 2 3 4 8 7 6 5 ICL7662 V+ D1 D2 C4 VOUT = (2V+) - (VFD1) - (VFD2) + - C2 + - C3 + - VOUT = - (nVIN - VFDX) C1 + - FIGURE 23. COMBINED NEGATIVE CONVERTER AND POSITIVE DOUBLER 1 2 3 4 8 7 6 5 + - + - 50 µF 50 µF + - 50 µF RL1 VOUT = V+ - V- 2 ICL7662 V+ V- RL2 FIGURE 24. SPLITTING A SUPPLY IN HALF 1 2 3 4 8 7 6 5 + - 100 µF ICL7662 100 µF VOUT + - 10 µF ICL7611 + - 100 Ω 50K +8V 100K 50K ICL8069 56K +8V 800K 250K VOLTAGE ADJUST + - FIGURE 25. REGULATING THE OUTPUT VOLTAGE ICL7662 All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com |
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