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TC7660HEPA датащи(PDF) 3 Page - Microchip Technology |
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TC7660HEPA датащи(HTML) 3 Page - Microchip Technology |
3 / 8 page 3 HIGH FREQUENCY 7660 DC-TO-DC VOLTAGE CONVERTER TC7660H TC7660H-2 10/1/96 © 2001 Microchip Technology Inc. DS21466A Detailed Description The TC7660H contains all the necessary circuitry to implement a voltage inverter, with the exception of two external capacitors, which may be inexpensive 1.0 µF non-polarized capacitors. Operation is best understood by considering Figure 2, which shows an idealized voltage inverter. Capacitor C1 is charged to a voltage, V+, for the half cycle when switches S1 and S3 are closed. (Note: Switches S2 and S4 are open during this half cycle.) During the second half cycle of operation, switches S2 and S4 are closed, with S1 and S3 open, thereby shifting capacitor C1 negatively by V+ volts. Charge is then transferred from C1 to C2, such that the voltage on C2 is exactly V+, assuming ideal switches and no load on C2. V+ GND S3 S1 S2 S4 C2 VOUT = – VIN Figure 2. Idealized Charge Pump Inverter Figure 1. TC7660H Test Circuit 1 2 3 4 8 7 6 5 TC7660H + V+ (+5V) C1 1.0 µF + C2 1.0 µF RL IS To improve low-voltage operation, the LV pin should be connected to GND. For supply voltages greater than 3.5V, the LV terminal must be left open to ensure latch-up- proof operation and prevent device damage. Theoretical Power Efficiency Considerations In theory, a capacitative charge pump can approach 100% efficiency if certain conditions are met: (1) The drive circuitry consumes minimal power. (2) The output switches have extremely low ON resistance and virtually no offset. (3) The impedances of the pump and reservoir capacitors are negligible at the pump frequency. The TC7660H approaches these conditions for nega- tive voltage multiplication if large values of C1 and C2 are used. Energy is lost only in the transfer of charge between capacitors if a change in voltage occurs. The energy lost is defined by: E = 1/2 C1 (V12 – V22) V1 and V2 are the voltages on C1 during the pump and transfer cycles. If the impedances of C1 and C2 are relatively high at the pump frequency (refer to Figure 1), compared to the value of RL, there will be a substantial difference in voltages V1 and V2. Therefore, it is not only desirable to make C2 as large as possible to eliminate output voltage ripple, but also to employ a correspondingly large value for C1 in order to achieve maximum efficiency of operation. Do's and Don'ts • Do not exceed maximum supply voltages. • Do not connect LV terminal to GND for supply voltages greater than 3.5V. • Do not short circuit the output to V+ supply for voltages above 5.5V for extended periods; however, transient conditions including start-up are okay. • When using polarized capacitors in the inverting mode, the + terminal of C1 must be connected to pin 2 of the TC7660H and the + terminal of C2 must be connected to GND Pin 3. |
Аналогичный номер детали - TC7660HEPA |
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Аналогичное описание - TC7660HEPA |
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