SP522CT datasheet(16/23 Pages) SIPEX

16 / 23 page

Rev. 7/10/03

SP522 Multi–Mode Serial Transceivers

APPLICATIONS INFORMATION

DCE-DTE Applications

A serial port can be easily configured for DTE

and DCE using multiple SP522 and/or SP524

parts. As shown on Figure 14, the transceivers

are half-duplexed to provide convenient DCE-

DTE capability. The driver outputs are con-

nected to the receiver inputs with only one pair

out to the serial port for each driver/receiver.

When the driver is tri-stated by applying a logic

low ("0") to ENT, the receivers can be active to

receive the appropriate input. The driver output

during tri-state is high impedance, therefore

will not degrade the signal levels of the receiver

input signal. When the receiver is tri-stated by

applying a logic ("1") to ENR, the driver output

is active to drive the appropriate signal without

interference from the receiver. The receiver

inputs are at least 12k

Ω to ground during tri-state.

Configuring Additional Multi-Protocol

Transceivers

Serial ports usually can have two data signals

(SD, RD), three clock signals (TT, ST, RT), and

at least eight control signals (CS, RS, etc.).

EIA-RS-449 contains twenty six signal types

including for a DB-37 connector. A DB-37

serial port design may require thirteen drivers

and fourteen receivers.

Although many

applications do not use all these signals, some

applications may need to support extra

functions such as diagnostics. Sipex's SP504

supports enough transceivers for the primary

channels of data, clock and control signals.

Configuring LL, RL and TM may require two

additional drivers and one receiver if designing

for a DTE (one driver and two receivers for a

DCE).

The SP522 and SP524 is a convenient solution

in a design that requires two extra single ended

or differential transceivers. The SP504 and

SP522, shown in Figure 15, can be programmed

in various configurations.

The SP504 is

programmed for RS-449 mode. By connecting

the decoder pins of the SP504 to the DP0 and

DP1 pins accordingly, the SP522 is programmed

in RS-423 mode. This adds two single ended

transceivers to the application. For applications

needing more than five RS-422 transceivers or

more than three RS-423 transceivers, the SP504

can be programmed to RS-422 whereas a SP524

can be added and programmed to RS-423, thus

creating seven RS-422 channels and four

RS-423 channels. The SP504 and the SP522/

SP524 can be configured to custom fit the

various serial port application needs.

+5V Only Operation Using the SP782

The SP522 and SP524 use external +10V or

+5V voltage supplies for power to maintain the

RS-232 and RS-423 voltage levels, respectively.

However, if a low-cost +5V solution if pre-

ferred, the SP522 and SP524 can be configured

with the SP782 or SP784 programmable charge

pump. The Sipex patent-pending programmable

charge pumps offer +10V or +5V outputs. The

programmability is used for switching from

RS-232 using the +10V outputs to RS-423 using

the +5V outputs. The SP782 requires 0.1

µF

capacitors and the SP784 requires 10

µF capacitors

for the charge pump. Please refer to the SP782

and SP784 data sheet for details on the program-

mable charge pump.

Achieving +10V with +12V Supplies

Since the SP522 and SP524 use external +10V

supplies, systems that have +12V supplies must

be regulated down to +10V. This can be simply

configured by placing diodes in series with the

DD and VSS lines. The absolute maximum

supply voltage is +12V. Since most +12V power

supplies have some voltage tolerances, usually

+10%, any increase above the 12V maximum

will damage the device. However, the +12V

supply may be used providing that the maximum

supply voltages do not exceed the rated absolute

maximum V

SS and VDD.

Sequencing of Power Supplies

Power Supplies for the SP522 and SP524 must

be sequenced. The recommended sequence is

CC first, VDD 50-80µSec later and VSS 100 to

1,000

µSec after V

DD. There are no sequencing

requirements for the SP522 or SP524 when they

are powered from either the SP782 or SP784

charge pump devices or from the V

DD and VSS

supply pins of the SP504 or SP505 charge pump

powered devices. For further details, see the

application note, V

DD, VCC and VSS Power

Supply Sequencing.

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