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SP504 Datasheet(PDF) 16 Page - Exar Corporation |
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SP504 Datasheet(HTML) 16 Page - Exar Corporation |
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16 / 32 page  6 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 Since both V DD and VSS are separately gen- erated from V CC in a no–load condition, VDD and V SS will be symmetrical. Older charge pump approaches that generate V– from V+ will show a decrease in the magnitude of V– compared to V+ due to the inherent inefficiencies in the design. The clock rate for the charge pump typically operates at 5kHz. The external capacitors must be a minimum of 22µF with a 6V breakdown rating. External Power Supplies For applications that do not require +5V only, externalsuppliescanbeappliedattheV+and V– pins.The value of the external supply volt- ages must be no greater than ±l0.5V.The tol- eranceshouldbe±5%from±0V.Thecurrent drain for the supplies is used for RS-232 and RS-423 drivers. For the RS-232 driver, the current requirement will be 3.5mA per driver. The RS-423 driver worst case cur- rent drain will be mA per driver. Power sequencing is required for the SP504. The supplies must be sequenced accordingly: +0V, +5V and –0V. An external circuit would be needed for proper power supply sequencing. Consult factory for application circuitry. Drivers The SP504 has seven (7) enhanced in- dependent drivers. Control for the mode selection is done via a four–bit control word. The drivers are pre-arranged such that for each mode of operation, the relative posi- tion and functionality of the drivers are set up to accommodate the selected interface mode.As the mode ofthe drivers is changed, the electrical characteristics will change to support the requirements of clock, data, and control line signal levels. Table shows the mode of each driver in the different interface modes that can be selected. There are four basic types of driver circuits — RS-232, RS-423, RS-485 and V.35. The RS-232 drivers output single–ended signals with a minimum of ±5V (with 3kΩ and 2500pF loading), and can operate up to 20kbps. The RS-232 drivers are used in RS- 232 mode for all signals, and also in V.35 mode where they are used as the control line signals such as DTR and RTS. The RS-423 drivers are also single–ended signals with a minimum voltage output of ±3.6V (with 450Ω loading) and can operate up to 20kbps. Open circuit V OL and VOH measurements are ±4.0V to ±6.0V. The RS- 423 drivers are used in RS-449, EIA-530, EIA-530A and V.36 modes as Category II signals from each of their corresponding specifications. Thethirdtypeofdriverproducesadifferential signal that can maintain RS-485, ±.5V dif- ferential output levels with a worst case load of 54Ω.The signal levels and drive capability of the RS-485 drivers allow the drivers to also support RS-422 (V.) requirements of ±2V differential output levels with 100Ω loads. The RS-422 drivers are used in RS- 449, EIA-530, EIA-530Aand V.36 modes as Category I signals which are used for clock and data. The fourth type of driver is the V.35 driver. V.35 levels require ±0.55V driver output sig- nals with a load of 100Ω. The SP504 drivers simplify existing V.35 implementations that use external termination schemes. The drivers were specifically designed to comply with the requirements of V.35 as well as the driver output impedance values of V.35. The drivers achieve the 50Ω to 150Ω source impedance. However, an external 150Ω resistor to ground must be connected to the non-inverting outputs; SD(b), ST(b), and TT(b), in order to comply with the 135Ω to 165Ω short-circuit impedance for V.35. The V.35 driver itself is disabled and transparent when the decoder is in all other modes. All of the differential drivers; RS-485, RS-422, and V.35, can operate up to 0Mbps. The driver inputs are both TTL or CMOS compatible. Since there are no pull-up or pull-down resistors on the driver inputs, they should be tied to a known logic state in order to define the driver output. |
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