sp304ct Exar Corporation, sp304ct Datasheet - Page 5

• Manufacturer Part Number: sp304ct
• Description: Rs-232/rs-422 Line Drivers/receivers
• Manufacturer: Exar Corporation

Figure 1. Isolating the SP304 from Ground.
+4.0V for V
derated performance can be expected.
POWER SUPPLY SEQUENCING
There are no special power–up sequencing re-
quirements for the SP304.
GENERAL USAGE
RS-232 Operation
The SP304 is a fully compliant RS-232 device.
Its outputs are fully protected against shorts to
exists for momentary shorts to voltages greater
than
resistor be wired in series with each driver
output. This will limit any damage from the
higher short-circuit current from these higher
voltage potentials. Voltage clamps such as back-
to-back Zener diodes can be used to clamp the
driver outputs to “safe” levels. Short circuit
current to ground is internally limited, and can
therefore be sustained infinitely. Under normal
operating conditions, the drivers can typically
source 7mA at 5V output, which exceeds the
minimum RS-232 standards requirement.
If an SP304 transmitter output occupies a data
SIGNAL PROCESSING EXCELLENCE
a) Single SP304
b) Multiple SP304
20V with no external circuitry. If the potential
Corporation
20V, it is recommended that a 220
3.3kΩ
3.3k Ω
CC
Q
3
Q
2N2222
. Under these supply conditions,
3
2N2222
3.3kΩ
3.3k Ω
Q
V
4
Q
DD
V
4
DD
V
GND
V
GND
DD
DD
V
GND
SP304
SP304
DD
SP304
V
V
V
V
CC
EE
CC
EE
V
V
CC
EE
V
V
CC
EE
V
V
CC
EE
transmission line with other RS-232 devices
which are not powered by the same power
supplies, it is possible that a device that is not
powered will have a low impedance path to
ground at its driver output. The RS-232 stan-
dards require that with no power applied to the
device, the impedance from a transmitter output
to ground must be greater than 300 . This can
be easily achieved as shown in Figure 1a, where
an external transistor is used as a switch to
isolate an SP304 from ground in the power off
condition. With V
switch is on, connecting ground (GND) for the
device to the circuit ground. In a power-off
condition, this transistor is switched off, thus
isolating the unit from circuit ground, and thereby
leaving the driver in a high impedance state.
Multiple SP304s can be connected as shown in
Figure 1b.
RS-422 OPERATION
The SP304 is a fully compliant RS-422 device
when operating in the RS-422 mode. Baud rate
and drive capability have been balanced to pro-
vide as much versatility as possible. The SP304
is both guaranteed for a 1Mbps data rate,
Figure 2. Typical Circuit
3.3K Ω
Q
3
2N2222
3.3K Ω
ROB
ROB
ROA
Q
TIB
TIB
TIA
V
4
DD
1
2
1
1
2
1
DD
V
GND
DD
turned on, the transistor
SP304
V
V
CC
EE
RIB
TOB
TOB
TOA
TOA
RIB
RIA
RIA
V
V
1
2
1
2
SELECT A = 1
SELECT B = 0
LOOPBACK = 1
1
2
1
2
CC
EE
81