Date: 10/1/05 SP322 V.11/V.35 Serial Transceiver © Copyright 2005 Sipex Corporation
10
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 V
SS
outputs
provide only 3mA of output current and should
not be connected to bias other external circuitry.
Recommended charge pump capacitor values
are 1µF 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
, V
T
, V
OS
, 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 54Ω as opposed to ±2.0V with a
100Ω 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 (100Ω ±50Ω)
and driver output short-circuit impedance (150Ω
±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 12kΩ. 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.
