SP503AN

SP503 Application Note

© Copyright 2000 Sipex Corporation

9

In DTE mode; TxD, TxC, RTS, DTR are the

drivers and RxD, RxC, CTS, DSR, DCD are the

receivers. Since there are seven drivers and

seven receivers in the SP503, the designer can

easily use the SP503 for the above signals. Other

RS-232 applications will support diagnostic func-

tions such as LL (driver), RL (driver), and TM

(receiver) which may or may not require extra

transceivers depending if other signals are not

used. Since Test Mode (TM) is a receiver for

DTE designs, the Ring Indicator (RI) receiver in

the SP503 (pin 21) can be used for TM if RI is not

used. If all the available drivers and receivers are

used in the SP503, then another RS-232 trans-

ceiver can be added. See page 230 and 231 for

suggestions on adding Sipex's RS-232 and

RS-485 transceivers.

Are the Schottky diodes used from Vcc to Vss

and from Vdd to C2- in the SP502 necessary for

the SP503?

Sipex has incorporated the Schottky diodes

(needed with the SP502) into the SP503 in order

to protect against potential start up problems due

to fast rate of rise on V

age to the TTL inputs. However, a negative

voltage (V

while the SP503 is powered off will cause start-

up problems to the charge pump. In order to

guard against this condition, an external Schottky

diode should be placed from V

minimize V

strate and allow the charge pump to operate

properly.

See page 203 Figure 6 - Typical

Operating Circuit, for diode connection

schematic.

Can the SP503 be configured for V.36?

CCITT Recommendation V.36 is similar to RS-

449 where certain signals are RS-422 signals and

others are RS-423. Depending on different ap-

plications; "Transmit Data", "Terminal Timing",

"Request-to-Send", "Data Terminal Ready",

"Receive Data", "Transmit Clock", "Receive

Clock", "Clear-to-Send", "Data Carrier Detect",

and "DataSet Ready" are specified as Category 1

Circuits where the protocol is RS-422 for rates

over 20kbps. All other circuits are Category 2

Circuits which are specified as RS-423 circuits.

Depending on particular signals, the SP503 can

be easily used for V.36.

When the two drivers, ST and TT, are in tri-state

mode, what will the driver outputs tolerate for

maximum short circuit voltages? And the re-

ceiver, SCT, input?

The driver outputs will tolerate up to

±16.0V

without any damage to the circuit regardless of

whether or not ST and TT are in tri-state mode.

The tri-state circuitry does not affect the short

circuit protection on the driver outputs. The SCT

receiver input will tolerate up to

±16.0V without

any damage to the input structure regardless of

whether or not SCT is in tri-state mode.

What does Sipex recommend for transient volt-

age suppression techniques for the SP503?

For our evaluation boards, Sipex uses transient

voltage suppressor ICs from ProTek Devices,

model numbers LCA05C to LCA15C. The two

digits in the part number pertain to the rated

stand-off voltage, V

working DC voltage applied to the device. These

TVS devices are especially designed for serial

data communications because of their low ca-

pacitance and low impedance. However, please

be aware that V

input range of the transceiver will affect the input

impedance. For example, it would be fine to use

a 5V V

receiver input voltage range is

±15Vwherelower

V

Another recommended manufacturer is AVX

Corporation TransGuard series of TVS compo-

nents. AVX offers a variety of surface mount

back-to-back diodes.

ProTek Devices • P.O. Box 3129 • Tempe, AZ. 85280

• 602-431-8101

AVX Corporation • Myrtle Beach, SC • 803-448-9411

The drawing on page 232 shows the SP503

configured with the ProTek SM16LC15C TVS

devices to protect the drivers and receivers from

ESD and over-voltage.

Will the SP503 conform to the physical layer

testing specified by NET1/NET2 for X.21 and

X.25 systems?

Sipex initiated a component level test for NET1/

NET2 for V.28, V.10, V.11, V.35 protocols. The

SP503 passed all the physical layer testing re-

quirements prescribed by NET1/NET2. A full

test report can be furnished upon request.