SP504 datasheet(15/31 Pages) SIPEX

15 / 31 page

Rev: A Date:1/27/04

SP504 Multi–Mode Serial Transceivers

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 sig-

nals with a minimum voltage output of

±3.6V

(with 450

Ω loading) and can operate up to

120kbps. Open circuit V

OL and VOH measure-

ments 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.

The third type of driver produces a differential

signal that can maintain RS-485,

±1.5V differ-

ential output levels with a worst case load of

Ω. The signal levels and drive capability of

the RS-485 drivers allow the drivers to also

support RS-422 (V.11) requirements of

±2V

differential output levels with 100

Ω loads. The

RS-422 drivers are used in RS-449, EIA-530,

EIA-530A and V.36 modes as Category I sig-

nals 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 100

Ω. The SP504 drivers

simplify existing V.35 implementations that use

external termination schemes. The drivers were

specifically designed to comply with the re-

quirements of V.35 as well as the driver output

impedance values of V.35. The drivers achieve

the 50

Ω to 150Ω source impedance. However,

an external 150

Ω resistor to ground must be

connected to the non-inverting outputs; SD(b),

ST(b), and TT(b), in order to comply with the

135

Ω to 165Ω short-circuit impedance for V.35.

The V.35 driver itself is disabled and transpar-

ent when the decoder is in all other modes. All

of the differential drivers; RS-485, RS-422, and

V.35, can operate up to 10Mbps.

The driver inputs are both TTL or CMOS com-

patible. 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.

Since both V

DD and VSS are separately gener-

ated from V

CC in a no–load condition, VDD and

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 15kHz. The external capacitors must

be a minimum of 22

µF with a 16V breakdown

rating.

External Power Supplies

For applications that do not require +5V only,

external supplies can be applied at the V+ and

V– pins. The value of the external supply volt-

ages must be no greater than

±l0.5V. The toler-

ance should be

±5% from ±10V. The current

drain for the supplies is used for RS-232 and

RS-423 drivers. For the RS-232 driver, the cur-

rent requirement will be 3.5mA per driver. The

RS-423 driver worst case current drain will be

11mA per driver. Power sequencing is required

for the SP504. The supplies must be sequenced

accordingly: +10V, +5V and –10V. An external

circuit would be needed for proper power sup-

ply sequencing. Consult factory for application

circuitry.

Drivers

The SP504 has seven (7) enhanced independent

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 position and functionality of the

drivers are set up to accommodate the selected

interface mode. As the mode of the drivers is

changed, the electrical characteristics will change

to support the requirements of clock, data, and

control line signal levels. Table 1 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 120kbps.

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