SP320 Datasheet, PDF (4/12 Pages) Sipex Corporation – Complete +5V-Only V.35 Interface with RS-232 V.28 Control Lines

THEORY OF OPERATION
±10Ω.
The SP320 is a single chip +5V-only serial
transceiver that supports all the signals
necessary to implement a full V.35 interface.
Three V.35 drivers and three V.35 receivers
make up the clock and data signals. Four
RS-232 (V.28) drivers and four RS-232 (V.28)
receivers are used for control line signals for
the interface.
V.35 Drivers
The V.35 drivers are +5V-only, low power
voltage output transmitters. The drivers do
not require any external resistor networks,
and will meet the following requirements:
1. Source impedance in the range of 50Ω
to 150Ω.
2. Resistance to ground of 150Ω ±15Ω,
measured from short-circuited terminals.
All of the V.35 receivers can operate at data
rates as high as 5Mbps. The sensitivity of
the V.35 receiver inputs is ±300mV.
RS-232 (V.28) Drivers
The RS-232 drivers are inverting transmit-
ters, which accept either TTL or CMOS
inputs and output the RS-232 signals with
an inverted sense relative to the input logic
levels. Typically, the RS-232 output voltage
swing is ±9V with no load, and ±5V minimum
with full load. The transmitter outputs are
protected against infinite short-circuits to
ground without degradation in reliability.
2. Resistance between short-circuited ter-
minals and ground is 150Ω ±15Ω.
3. When terminated with a 100Ω resistive
load the terminal to terminal voltage will be
0.55 Volts ±20% so that the A terminal is
positive to the B terminal when binary 0 is
transmitted, and the conditions are reversed
to transmit binary 1.
4. The arithmetic mean of the voltage of the
A terminal with respect to ground, and the B
terminal with respect to ground will not
exceed 0.6 Volts when terminated as in 3
above.
The V.35 drivers can operate at data rates
as high as 5Mbps. The driver outputs are
protected against short-circuits between
the A and B outputs and short circuits to
ground.
Two of the V.35 drivers, DRIN2 and DRIN3
are equipped with enable control lines. When
the enable pins are high the driver outputs are
disabled, the output impedance of a disabled
driver will nominally be 300Ω. When the en-
able pins are low, the drivers are active.
V.35 Receivers
The V.35 receivers are +5V only, low power
differential receivers which meet the follow-
ing requirements:
1. Input impedance in the range of 100Ω
In the power off state, the output imped-
ance of the RS-232 drivers will be greater
than 300Ω over a ±2V range. Should the
input of a driver be left open, an internal
400kΩ pullup resistor to V_CC forces the
input high, thus committing the output to
a low state. The slew rate of the trans-
mitter output is internally limited to a
maximum of 30V/µs in order to meet the EIA
standards. The RS-232 drivers are rated for
120kbps data rates.
RS-232 (V.28) Receivers
The RS-232 receivers convert RS-232
input signals to inverted TTL signals. Each
of the four receivers features 500mV of
hysteresis margin to minimize the effects
of noisy transmission lines. The inputs also
have a 5kΩ resistor to ground; in an open
circuit situation the input of the receiver
will be forced low, committing the output
to a logic high state. The input resistance
will maintain 3kΩ-7kΩ over a ±15V range.
The maximum operating voltage range for the
receiver is ±30V, under these conditions the
input current to the receiver must be limited
to less than 100mA. The RS-232 receivers
can operate to beyond 120kbps.
CHARGE PUMP
The charge pump is an Exar patented design
(U.S. 5,306,954) and uses a unique approach
compared to older less-efficient designs.
The charge pump still requires four external
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com

SP320_100_092208