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SP3225EEA-L Datasheet(PDF) 11 Page - Sipex Corporation |
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SP3225EEA-L Datasheet(HTML) 11 Page - Sipex Corporation |
11 / 23 page 11 Rev P 11/20/06 SP3224E-SP3227E Transceivers with Auto On-line® Plus © 2006 Sipex Corporation THEORY OF OPERATION Description The SP3224E and SP3225E are 2-driver/ 2-receiver devices. The SP3226E and SP3227E are 1-driver/1-receiver devices. All are ideal for serial ports in embedded, consumer, portable, or handheld applica- tions. The transceivers meet the EIA/TIA- 232 and ITU-T V.28/V.24 communication protocols for reliable serial communication. The devices feature 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 SP3224E-SP3227E are ideal choic- es for power sensitive designs. With the Auto On-line® Plus enabled, the SP3224E- SP3227E reduce supply current to 1µA whenever the transceivers are in idle. In shutdown, the internal charge pump and the drivers will shut down. This feature al- lows design engineers to address power saving concerns without major design changes. Theory Of Operation The SP3224E-SP3227E are made up of four basic circuit blocks: 1. Drivers, 2. Re- ceivers, 3. the Sipex proprietary charge pump, and 4. Auto On-line® Plus circuitry. Drivers The drivers are inverting level transmit- ters that convert TTL or CMOS logic lev- els to 5.0V EIA/TIA-232 levels with an inverted sense relative to the input logic levels. Typically, the RS-232 output volt- age 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 reliabili- ty. These drivers comply with the EIA-TIA- 232-F and all previous RS-232 versions. Unused driver inputs should be connected to GND or VCC. The drivers can guarantee output data rates fully loaded with 3KΩ in parallel with 1000pF (SP3224E/SP3226E), or 3KΩ in parallel with 250pF (SP3225E/SP3227E) ensuring compatibility with PC-to-PC com- munication software. The slew rate of the driver output on the SP3224E/SP3226E 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 Slew Rate of SP3225E/SP3227E is not limited to enable higher speed data transfers. The transition of the loaded output from HIGH to LOW also meets the monotonic signal transition requirements of the standard. Receivers The receivers convert EIA/TIA-232 signal levels to TTL or CMOS logic output lev- els. Receivers remain active during device shutdown. Since receiver input is usually from a transmission line where long cable lengths and system interference can de- grade the signal, the inputs have a typical hysteresis margin of 500mV. This ensures that the receiver is virtually immune to noisy transmission lines. Should an input be left unconnected, an internal 5KΩ pulldown re- sistor to ground will commit the output of the receiver to a HIGH state. Charge Pump The charge pump is a Sipex–patented de- sign (US Patent #5,306,954) and uses a unique approach compared to older less- efficient designs. The charge pump still requires four external capacitors, but uses a four phase voltage shifting technique to attain symmetrical 5.5V power supplies. The internal power supply consists of a regulated dual charge pump that provides output voltages 5.5V regardless of the in- put voltage (Vcc) over the +3.0V to +5.5V range. This is important to maintain com- pliant RS-232 levels regardless of power supply fluctuations. The charge pump operates in a discontinu- ous mode using an internal oscillator. If the output voltages are less than a magnitude |
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