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SP232AEN Datasheet(PDF) 5 Page - Exar Corporation |
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SP232AEN Datasheet(HTML) 5 Page - Exar Corporation |
5 / 10 page 5 Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • Fax (50)668-707 • www.exar.com SP232A_00_05308 DESCRiPTion Phase 4 Vdd transfer. The fourth phase connects the negative terminal of C2 to ground and the posi- tive terminal of C2 to the Vdd storage capacitor . This transfers the doubled (V+) voltage onto C3. Meanwhile, capacitor C is charged from Vcc to prepare it for its next phase. Under lightly loaded conditions, the intelligent pump oscillator maximizes efficiency by running only as needed to maintain V+ and V- voltage levels. Since interface transceivers spend most of their time at idle, this power-efficient innova- tion can greatly reduce total power consump- tion. This improvement is made possible by the independent phase sequences of the Exar charge pump design. The clock rate of the charge pump typically op- erates greater than 70kHz allowing the pump to operate efficiently with small 0.1uF capacitors. Efficient operation depends on rapid charging and discharging of C and C2. Therefore, the capacitors should be mounted as close as pos- sible to the IC and have a low ESR (equivalent series resistance). Inexpensive, surface mount ceramic capacitors are ideal for use on charge pump. If polarized capacitors are used the posi- tive and negative terminals should be connect- ed as shown on the typical operating circuit. A diagram of the 4 individual phases is shown in Figure . C 2 + - V CC C 3 C 4 C 1 + + + e- e- Phases 1 and 3: Store/Double. Double charge from C1 onto C2. C2 is now charged to -2xVcc + C 2 + - V CC C 3 C 4 C 1 + + + e- + e+ e+ C 2 + - V CC C 3 C 4 C 1 + + + Phase 2 – Vss transfer from C2 to C4. Meanwhile C1 is charged to Vcc e- e- e- + Vss transfer from C2 to C3. Meanwhile C1 is charged to Vcc V DD V- V+ V- V+ V+ Patented 5,306,954 Phase 4 VDD Figure . Charge pump phases |
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