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SP202ECT-L Datasheet(PDF) 6 Page - Exar Corporation |
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SP202ECT-L Datasheet(HTML) 6 Page - Exar Corporation |
6 / 17 page Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • www.exar.com SP202E,232E,233E, 30E, 32E_00_0608 6 DESCRiPTion C is charged from Vcc to prepare it for its next phase. Phase 3 Vdd charge store and double: Phase three is identical to the first phase. The positive termi- nals of C and C2 are charged from Vcc with their negative terminals initially connected to ground. C+ is then connected to ground and the stored charge from C- is superimposed onto C2-. Since C2+ is still connected to Vcc the voltage potential across capacitor C2 is now 2 x Vcc. 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. The clock rate for the charge pump typically op- erates at greater than 5kHz allowing the pump to run efficiently with small 0.1uF capacitors. Ef- ficient operation depends on rapid charging and discharging of C and C2, therefore capacitors should be mounted as close as possible to the IC and have low ESR (equivalent series resis- tance). Inexpensive surface mount, ceramic ca- pacitors are ideal for using on charge pump. If polarized capacitors are used the positive and negative terminals should be connected as shown in the typical operating circuit. A diagram of the individual phases are shown in Figure . Shutdown (SD) and Enable (En) features for the SP310E and SP312E Both the SP30E and SP32E have a shutdown / standby mode to conserve power in battery- powered applications. To activate the shutdown mode, which stops the operation of the charge pump, a logic "0" is applied to the appropriate control line. For the SP30E, this control line is the ON/OFF (pin 8) input. Activating the shut- down mode puts the SP30E transmitter and receiver ouptuts into a high impedance con- dition. For the SP32E, this control line is the SHUTDOWN (pin8) input; this also puts the transmitter outputs in a tri-state mode. The re- ceiver outputs can be tri-stated seperately dur- ing normal operation or shutdown by applying a logic "" on the EN line (pin ). Wake-Up Feature for the SP312E The SP32E has a wake-up feature that keeps the receivers active when the device is placed into shutdown. Table 1 defines the truth table for the Wake-Up function. When only the receivers are activated, the SP32E typically draws less than 5uA supply current. In the case of when a modem is interfaced to a computer in power down mode, the Ring Indicator (RI) signal from the modem would be used to "wake-up" the computer, allowing it to accept data transmis- sion. After the ring indicator has propagated through the SP32E receiver, it can be used to trigger the power management circuitry of the computer to power up the microproces- sor, and bring the SD pin of the SP32E to a logic high, taking it out of the shutdown mode. The receiver propagation delay is typically us. The enable time for V+ and V- is typi- cally 2ms. After V+ and V- have settled to their final values, a signal can be sent back to the modem on the data terminal ready (DTR) pin signifying that the computer is ready to accept the transmit data. SD EN Power Up/Down Receiver outputs 0 0 Down Enabled 0 Down Tri-state 0 Up Enabled Up Tri-state Table . Wake-up Function truth table Pin Strapping for the SP233E To operate properly, the following pairs of pins must be externally wired together as noted in table 2: Pins Wired Together SOICW Two V- pins 0 & 7 Two C2+ pins 2 & 5 Two C- pins & 6 Connect Pins 6 and 9 to GND Table 2. Pin Strapping table for SP233E |
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