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SP504 Datasheet(PDF) 14 Page - Exar Corporation |
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SP504 Datasheet(HTML) 14 Page - Exar Corporation |
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14 / 32 page  4 Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com SP504_02_2708 Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com SP504_02_2708 FEATURES… The SP504isahighlyintegratedserial trans- ceiverthatallowssoftwarecontrolofitsinter- facemodes.SimilartotheSP503,the SP504 offers the same hardware interface modes for RS-232 (V.28), RS-422A(V.), RS-449, RS-485,V.35,EIA-530andincludesV.36and EIA-530A. The interface mode selec- tion is done via an 8–bit switch; four (4) bits control the drivers and four (4) bits control the receivers. The SP504 is fabricated using low power BiCMOS process technology, and incorporates a Exar patented (5,306,954) charge pump allowing +5V only operation. Each device is packaged in an 80–pin JEDEC Quad FlatPack package. The SP504 is ideally suited for wide area network connectivity based on the interface modes offered and the driver and receiver configurations. The SP504 has seven (7) independent drivers and seven (7) indepen- dent receivers. In V.35 mode, the SP504 includes the necessary components and termination resistors internal within the de- vice for compliant V.35 operation. THEORY OF OPERATION The SP504 is made up of five separate circuit blocks — the charge pump, drivers, receivers,decoderandswitchingarray. Each of these circuit blocks is described in more detail below. Charge–Pump The SP504's charge pump design is based on the SP503 where Exar'spatentedcharge pump design (5,306,954) uses a four–phase voltage shifting technique to attain sym- metrical ±0V power supplies. In addition, the SP504 charge pump incorporates a "programmable" feature that produces an output of ±0V or ±5V for V SS and VDD depending on the mode of operation. The charge pump still requires external capaci- tors to store the charge. Figure 8a shows the waveform found on the positive side of capacitor C2, and Figure 8b shows the negative side of capcitor C2. There is a free–running oscillator that controls the four phases of the voltage shifting. A description of each phase follows. The SP504 charge pump is used for RS-232 where the output voltage swing is typically ±0V and also used for RS-423. However, RS-423 requires the voltage swing on the driver output be between ±4V to ±6V during an open circuit (no load). The charge pump would need to be regulated down from ±0V to ±5V. A typical ±0V charge pump would require external clamping such as 5V zener diodes on V DD and VSS to ground. The ±5V output has symmetrical levels as in the ±0V output. The ±5V is used in the following modes where RS-423 levels are used: RS- 449, EIA-530, EIA-530A and V.36. Phase 1 (±10V) — V SS charge storage — During this phase of the clock cycle, the positive side of capaci- tors C and C2 are initially charged to +5V. The C l + is then switched to ground and the charge on C – is transferred to C 2 – . Since C 2 + is connected to +5V, the voltage potential across capacitor C 2 is now 0V. Phase 1 (±5V) — V SS & VDD charge storage and transfer — With the C and C2 capacitors initially charged to +5V, C l + is then switched to ground and the charge on C – is transferred to the V SS storage capacitor. Simultane- ously the C 2 – is switched to ground and the 5V charge on C 2 + is transferred to the V DD storage capacitor. VCC = +5V +5V VDD Storage Capacitor C1 C2 C4 + + + – – – VSS Storage Capacitor C3 + – –5V VCC= +5V –5V –5V +5V VDD Storage Capacitor C1 C2 C4 + + + – – – VSSStorage Capacitor C3 + – Figure 4a. Charge Pump Phase for ±0V. Figure 4b. Charge Pump Phase for ±5V. |
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