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TC7660SEPA713 Scheda tecnica(PDF) 11 Page - Microchip Technology |
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TC7660SEPA713 Scheda tecnica(HTML) 11 Page - Microchip Technology |
11 / 24 page 2001-2015 Microchip Technology Inc. DS20001467C-page 11 TC7660S 5.6 Combined Negative Voltage Conversion and Positive Supply Multiplication Figure 5-7 combines the functions shown in Figure 5-3 and Figure 5-6 to provide negative voltage conversion and positive voltage multiplication simultaneously. For example, this approach would be suitable for generat- ing +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 multiplied pos- itive 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. FIGURE 5-7: Combined Negative Converter and Positive Multiplier. 5.7 Efficient Positive Voltage Multiplication/Conversion Since the switches that allow the charge pumping operation are bidirectional, the charge transfer can be performed backwards as easily as forwards. Figure 5-8 shows a TC7660S transforming -5V to +5V (or +5V to +10V, etc.). The only problem is that the internal clock and switch-drive section will not operate until some positive voltage has been generated. An ini- tial inefficient pump, as shown in Figure 5-7, could be used to start this circuit up, after which it will bypass the other (D1 and D2 in Figure 5-7 would never turn on), or else the diode and resistor shown dotted in Figure 5-8 can be used to “force” the internal regulator on. FIGURE 5-8: Positive Voltage Conversion. 5.8 Voltage Splitting The same bidirectional characteristics used in Figure 5-8 can also be used to split a higher supply in half, as shown in Figure 5-9. The combined load will be evenly shared between the two sides. Once again, 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 5-3, +15V can be converted (via +7.5V and -7.5V) to a nominal -15V, though with rather high series resistance (~250Ω). FIGURE 5-9: Splitting a Supply in Half. 5.9 Negative Voltage Generation for Display ADCs The TC7106 is designed to work from a 9V battery. With a fixed power supply system, the TC7106 will perform conversions with input signal referenced to power supply ground. 5.10 Negative Supply Generation for 4½ Digit Data Acquisition System The TC7135 is a 4½ digit ADC operating from ±5V supplies. The TC7660S provides an inexpensive -5V source. (See AN16 and AN17 for TC7135 interface details and software routines.) + C1 D1 + + C3 C4 C2 D2 + VOUT = 1 2 3 4 8 7 6 5 TC7660S V+ (2 V+) - (2 VF) VOUT = -V+ VOUT = -V - + 1M V- input + 1 2 3 4 8 7 6 5 TC7660S 10 µF 10 µF C1 + R L1 R L2 V OUT = V + –V – 2 50 μF 100 k Ω 50 μF V + V – 50 μF + 1 M Ω 1 2 8 7 TC7660S 3 4 6 5 + – – |
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