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SP3222EH Datasheet(PDF) 8 Page - Sipex Corporation |
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SP3222EH Datasheet(HTML) 8 Page - Sipex Corporation |
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8 / 19 page  Date: 06/22/04 SP3222EH/3232EH 3.3V, 460 Kbps RS-232 Transceivers © Copyright 2004 Sipex Corporation 8 DESCRIPTION The SP3222EH and SP3232EH are 2-driver/ 2-receiver devices ideal for portable or hand-held applications. The SP3222EH features a 1 µA shutdown mode that reduces power consumption and extends battery life in portable systems. Its receivers remain active in shutdown mode, allowing external devices such as modems to be monitored using only 1 µA supply current. The SP3222EH/3232EH transceivers meet the EIA/TIA-232 and V.28/V.24 communication protocols. They feature Sipex's proprietary on-board charge pump circuitry that generates 2 x V CC for RS-232 voltage levels from a single +3.0V to +5.5V power supply. The SP3222EH/ 3232EH drivers operate at a minimum data rate of 460Kbps. THEORY OF OPERATION The SP3222EH/3232EH are made up of three basic circuit blocks: 1. Drivers, 2. Receivers, and 3. the Sipex proprietary charge pump. Drivers The drivers are inverting level transmitters that convert TTL or CMOS logic levels to +5.0V EIA/TIA-232 levels inverted relative to the input logic levels. Typically, the RS-232 output voltage swing is +5.5V with no load and at least +5V minimum fully loaded. The driver outputs are protected against infinite short-circuits to ground without degradation in reliability. Driver outputs will meet EIA/TIA-562 levels of +3.7V with supply voltages as low as 2.7V. The drivers have a minimum data rate of 460Kbps fully loaded with 3K Ω in parallel with 1000pF, ensuring compatibility with PC-to-PC communication software. The slew rate of the driver output is internally limited to a maximum of 30V/ µs in order to meet the EIA standards (EIA RS-232D 2.1.7, Paragraph 5). The transition of the loaded output from HIGH to LOW also meets the monotonicity requirements of the standard. Figure 8 shows a loopback circuit used to test the RS-232 drivers. Figure 9 shows the test results of the loopback circuit with all drivers active at 120Kbps and RS-232 loads in parallel with 1000pF capacitors. Figure 10 shows the test results where one driver is active at 460Kbps and all drivers are loaded with an RS-232 receiver in parallel with a 1000pF capacitor. The SP3222EH driver's output stages are tri-stated in shutdown mode. When the power is off, the SP3222EH device permits the outputs to be driven up to +12V. Because the driver's inputs do not have pull-up resistors, unused inputs should be connected to V CC or GND. In the shutdown mode, the supply current is less than 1 µA, where SHDN = LOW. When the SP3222EH device is shut down, the device's driver outputs are disabled (tri-stated) and the charge pumps are turned off with V+ pulled down to V CC and V- pulled to GND. The time required to exit shutdown is typically 100 µs. SHDN is connected to V CC if the shutdown mode is not used. SHDN has no effect on RxOUT or RxOUTB. As they become active, the two driver outputs go to opposite RS-232 levels: one driver input is HIGH and the other LOW. Note that the drivers are enabled only when the magnitude of V- exceeds approximately 3V. |
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