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SP3220ECY Datasheet(PDF) 8 Page - Sipex Corporation |
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SP3220ECY Datasheet(HTML) 8 Page - Sipex Corporation |
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8 / 18 page  11/07/02 SP3220E True +3.0 to +5.0V RS-232 Transceivers © Copyright 2002 Sipex Corporation 8 DESCRIPTION The SP3220E device meets the EIA/TIA-232 and V.28/V.24 communication protocols and can be implemented in battery-powered, portable, or hand-held applications such as notebook or palmtop computers. The SP3220E device features 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. This series is ideal for +3.3V-only systems, mixed +3.0V to +5.5V systems, or +5.0V-only systems that require true RS-232 performance. The SP3220E device has a driver that operates at a typical data rate of 235Kbps fully loaded. The SP3220E is a 1-driver/1-receiver device ideal for portable or hand-held applications. The SP3220E 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. THEORY OF OPERATION The SP3220E device is 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 typically can operate at a data rate of 235Kbps. The drivers can guarantee a data rate of 120Kbps 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. The SP3220E driver can maintain high data rates up to 235Kbps fully loaded. Figure 6 shows a loopback test circuit used to test the RS-232 driver. Figure 7 shows the test results of the loopback circuit with the driver active at 120Kbps with an RS-232 load in parallel with a 1000pF capacitor. Figure 8 shows the test results where the driver was active at 235Kbps and loaded with an RS-232 receiver in parallel with a 1000pF capacitor. A solid RS-232 data transmission rate of 120Kbps provides compatibility with many designs in personal computer peripherals and LAN applications. The SP3220E driver's output stage is turned off (high-Z) when the device is in shutdown mode. When the power is off, the SP3220E device permits the outputs to be driven up to +12V. The driver's input does not have pull-up resistors. Designers should connect an unused input to V CC or GND. In the shutdown mode, the supply current falls to less than 1 µA, where SHDN = LOW. When the SP3220E device is shut down, the device's driver output is disabled (high-Z) and the charge pump is turned off with V+ pulled down to V CC and V- pulled to GND. The time required to exit shutdown is typically 100 µs. Connect SHDN to V CC if the shutdown mode is not used. SHDN has no effect on RxOUT. Note that the driver is enabled only when the magnitude of V- exceeds approximately 3V. |
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