SP322 datasheet(10/14 Pages) SIPEX

10 / 14 page

Rev. 7/9/03

SP322 V.11/V.35 Serial Transceiver

THEORY OF OPERATION

The SP322 is a programmable V.11 or V.35

transceiver IC. It contains three driver and three

receivers which can be configured to either V.11

or V.35 physical layer electrical characteristics.

The transceivers within the SP322 include all

the necessary termination resistor networks

required for compliant V.11 and V.35 signals.

This simplifies serial port designs using V.11 or

V.35 where the engineer does not have to

configure V.11 cable termination resistors and

the V.35 network.

The SP322 contains four basic blocks: the

charge pump, differential drivers, differential

receivers, termination network circuitry. Each

block is described in the following.

Charge–Pump

The SP322 charge pump is smaller version of

the Sipex–patented design (U.S. 5,306,954).

The charge pump still requires four external

capacitors and uses a four–phase voltage shift-

ing technique to attain symmetrical 10V power

supplies. But the pump is only used for provid-

ing internal biasing for the transceivers and the

termination circuitry. The V

DD and VSS outputs

provide only 3mA of output current and should

not be connected to bias other external circuitry.

Recommended charge pump capacitor values

are 1

µF or greater. The internal oscillator pro-

vides a clock rate for the charge pump which

typically operates at 15kHz.

Drivers

The SP322 has three differential drivers. There

are two types of drivers includes within the

SP322: V.11 drivers and V.35 drivers.

When configured in V.11 mode, the V.11 driv-

ers produce a differential output compliant with

the V.11 and RS-422 electrical specifications.

This includes the all the DC electrical param-

eters such as V

OC, VT, VOS, etc. The strength of

the SP322 drivers allow them to also drive

signals per the RS-485 standard. The V

T mini-

mum of

±1.5V is provided by the driver output

given a load of 54

Ω as opposed to ±2.0V with a

100

Ω load for RS-422. However, the drivers are

not intended to operate over the RS-485 com-

mon mode range of +12V to -7V. The common

mode range for the V.11 drivers is +7V to -7V

which is in accordance to the ITU V.11 specifi-

cation.

When in V.35 mode, the drivers provide V.35

signals compliant to the ITU V.35 electrical

specification. Specifically, the V.35 driver is

designed to supply a differential output of

±0.55V

with an offset of less than 0.6V. With Sipex's

patent-pending V.35 driver design, the driver

also adheres to impedance measurements such

as driver output source impedance (100

Ω ±50Ω)

and driver output short-circuit impedance (150

Ω

±15Ω). Traditional V.35 drivers require a resis-

tor network to provide the proper V.35 imped-

ance specifications for the driver outputs. The

SP322 V.35 driver does this without the aid of

any external components attached to the driver

output. Its unique design contains internal

resistance matching and switching to provide

compliant V.35 signals.

Each driver includes an enable pin for added

convenience. The driver enable pins are low

active and will tri-state the driver outputs if a

logic "1" is applied. During this state, the drivers

are high impedance. The enable pins include a

pull-down resistor so that the pin can be

unconnected where the driver will always be

enabled. Regardless of physical protocol, the

drivers can operate to at least 10Mbps.

Receivers

The SP322 has three differential receivers which

are used for either V.11 or V.35. The receivers

have a 200mV sensitivity and operate over the

common mode range of +7V to -7V.

The

receiver itself is the same in either V.11 or V.35

mode. The receiver input termination is config-

ured differently for each mode (V.11/V.35 pin).

The receivers also include enable pins for con-

venience. The receiver enable pins are high

active where a logic "0" will tri-state the re-

ceiver outputs. During tri-state, the receiver

inputs are approximately 12k

Ω. Any termina-

tion associated with the operating mode is dis-

connected during tri-state of that receiver. The

receiver enable pins have a pull-up resistor that

allows the pins to be unconnected. The receiver

will always be active in this case. The differen-

tial receiver can operate to at least 10Mbps.

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