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TC682COA Scheda tecnica(PDF) 3 Page - TelCom Semiconductor, Inc |
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TC682COA Scheda tecnica(HTML) 3 Page - TelCom Semiconductor, Inc |
3 / 6 page 4-23 TELCOM SEMICONDUCTOR, INC. 7 6 5 4 3 1 2 8 Phase 2 VSS transfer – phase two of the clock connects the negative terminal of C2 to the negative side of reservoir capacitor C3 and the positive terminal of C2 to ground, transferring the generated – 10V to C3. Simultaneously, the positive side of capacitor C1 is switched to +5V and the negative side is connected to ground. C2 is then switched to VCC and GND and Phase 1 begins again. Figure 3. Charge Pump – Phase 2 DETAILED DESCRIPTION Phase 1 VSS charge storage – before this phase of the clock cycle, capacitor C1 is already charged to +5V. C1 + is then switched to ground and the charge in C1 – is transferred to C2– . Since C2 + is at +5V, the voltage potential across capacitor C2 is now –10V. Figure 2. Charge Pump – Phase 1 MAXIMUM OPERATING LIMITS The TC682 has on-chip zener diodes that clamp VIN to approximately 5.8V, and V – OUT to – 11.6V. Never exceed the maximum supply voltage or excessive current will be shunted by these diodes, potentially damaging the chip. The TC682 will operate over the entire operating temperature range with an input voltage of 2V to 5.5V. EFFICIENCY CONSIDERATIONS Theoretically a charge pump voltage multiplier can approach 100% efficiency under the following conditions: • The charge pump switches have virtually no offset and are extremely low on resistance. • Minimal power is consumed by the drive circuitry • The impedances of the reservoir and pump capaci- tors are negligible. For the TC682, efficiency is as shown below: Voltage Efficiency = VOUT / (– 2VIN) VOUT = – 2VIN + VDROP VDROP = (IOUT) (ROUT) Power Loss = IOUT (VDROP) There will be a substantial voltage difference between V – OUT and 2 VIN if the impedances of the pump capacitors C1 and C2 are high with respect to their respective output loads. Larger values of reservoir capacitor C3 will reduce output ripple. Larger values of both pump and reservoir capacitors improve the efficiency. See "Capacitor Selec- tion" in Applications section. APPLICATIONS Negative Doubling Converter The most common application of the TC682 is as a charge pump voltage converter which provides a negative output of two times a positive input voltage (Figure 4). Figure 4. Inverting Voltage Doubler V IN = +5V V OUT –5V SW4 SW1 SW2 SW3 C 2 C 3 C 1 + – + + – – +5V V OUT –10V SW4 SW2 SW1 SW3 C 2 C 3 C 1 + – + + – – C1 + C1 C2 C3 C2 + V IN V IN VOUT GND GND TC682 22 µF 22 µF 22 µF 7 6 5 4 3 2 1 VOUT C2 – C1 – – – INVERTING VOLTAGE DOUBLER TC682 |
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