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SP3238EEA Datasheet(PDF) 8 Page - Sipex Corporation |
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SP3238EEA Datasheet(HTML) 8 Page - Sipex Corporation |
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8 / 20 page  SP3238EDS/04 SP3238E +3.0V to +5.5V RS-232 Transceivers © Copyright 1999 Sipex Corporation 8 DESCRIPTION The SP3238E device meets the EIA/TIA-232 and ITU-T 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 SP3238E device features Sipex's proprietary and patented (U.S.-- 5,306,954) on-board charge pump circuitry that generates ±5.5V RS-232 voltage levels from a single +3.0V to +5.5V power supply. The SP3238E device can operate at a typical data rate of 250kbps fully loaded. The SP3238E is a 5-driver/3-receiver device, ideal for portable or hand-held applications. The SP3238E includes one complementary always-active receiver that can monitor an external device (such as a modem) in shutdown. This aids in protecting the UART or serial controller IC by preventing forward biasing of the protection diodes where V CC may be disconnected. The SP3238E device is an ideal choice for power sensitive designs. The SP3238E device features Auto-Online circuitry which reduces the power supply drain to a 1 µA supply current. In many portable or hand-held applications, an RS-232 cable can be disconnected or a connected peripheral can be turned off. Under these conditions, the internal charge pump and the drivers will be shut down. Otherwise, the system automatically comes online. This feature allows design engineers to address power saving concerns without major design changes. THEORY OF OPERATION The SP3238E device is made up of four basic circuit blocks: 1. Drivers, 2. Receivers, 3. the Sipex proprietary charge pump, and 4. Auto-Online circuitry. Drivers The drivers are inverting level transmitters that convert TTL or CMOS logic levels to 5.0V EIA/ TIA-232 levels with an inverted sense relative to the input logic levels. Typically, the RS-232 output voltage swing is +5.4V with no load and +5V minimum fully loaded. The driver outputs are protected against infinite short-circuits to ground without degradation in reliability. These drivers comply with the EIA-TIA-232F and all previous RS-232 versions. The drivers typically can operate at a data rate of 250kbps. 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. Figure 6. Interface Circuitry Controlled by Microprocessor Supervisory Circuit SP3238E 28 25 3 1 27 4 26 GND C1+ C1- C2+ C2- V+ V- VCC 0.1 µF 0.1 µF 0.1 µF + C2 C5 C1 + + C3 C4 + + 0.1 µF 0.1 µF 13 14 15 VCC 2 ONLINE SHUTDOWN STATUS µP Supervisor IC VCC VIN RESET 5k Ω 5k Ω 5k Ω 24 23 22 16 21 20 18 5 6 7 8 9 11 RS-232 OUTPUTS RS-232 INPUTS T 1IN R 1OUT R 1IN T 2OUT R 1OUT T 2IN T 3IN T 3OUT T 1OUT R 2IN R 3IN R 2OUT R 3OUT UART or Serial µC TxD RTS DTR RxD CTS DSR DCD RI 19 17 10 12 T 4OUT T 4IN T 5IN T 5OUT |
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