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PDF ISO422 Data sheet ( Hoja de datos )
| Número de pieza | ISO422 | |
| Descripción | DIFFERENTIAL BUS TRANSCEIVER | |
| Fabricantes | Burr-Brown Corporation | |
| Logotipo |  |
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® ISO422
ISO422
ISO422
DIFFERENTIAL BUS TRANSCEIVER
FEATURES
q FULL-/HALF-DUPLEX OPERATION
q 1500Vrms ISOLATION (cont)
q 2500Vrms ISOLATION (1 min)
q 2.5Mbps PERFORMANCE
q LOOP-TEST FACILITY
APPLICATIONS
q BUS TRANSMISSION SYSTEMS
q GROUND LOOP ISOLATION
DE
D
LBE
R
RE
DESCRIPTION
ISO422 provides 1500Vrms isolation for industrial
bus transmission systems. ISO422 may be configured
in full or half duplex modes providing the user with
best flexibility for the application. Transmission rates
of 2.5Mbps can be obtained covering most require-
ments. A loop-back test facility is included. LBE
allows data on the D input to be routed to the R output
for test purposes.
ISO422 is available in 24-pin PDIP and 24-pin Gull
Wing(1) packages and is specified over the temperature
range –40°C to +85°C.
NOTE: (1) Gull Wing version available Q1’99.
Y
Z
A
B
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111
Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©1998 Burr-Brown Corporation
PDS-1503A
Printed in U.S.A. December, 1998
1 page  
OPERATION
ISO422 is an isolated, full-duplex bus transceiver which is
compatible with three-wire data bus systems using EIA
standards RS-422-A and RS-485. It is based on Burr-Brown’s
capacitive barrier technology. The data bus input is designed
to present a very high impedance to the data bus, thus
allowing a virtually unlimited number of receivers on any
data bus section. To allow this feature, the data bus input is
limited to a common-mode range within the magnitude of
the supplies. This limitation requires that all nodes on the
bus are referenced to a common ground. However, systems
attached to the bus through ISO422, are isolated up to
1500Vrms and may, therefore, have local floating ground
potentials up to this isolation voltage. The circuit encodes all
data passed across the barrier to ensure that the input values
and control signals are correctly passed across the barrier
under all power up conditions. The ISO422 also allows data
recovery to the current input state, after any transient upset.
TRANSMIT
Data is passed from the D input to the data bus outputs after
a barrier transmission delay (tDD) when the DE input is
HIGH. When DE is LOW, the data bus drivers are switched
off, and assume the high impedance state. When enabling
the data bus output, i.e., switching DE from LOW to HIGH,
the enable signal is passed directly across the barrier and
enables the output, after a barrier transmission delay and
output enable time (tDLZ/tDHZ). Similarly, when disabling the
data bus output, i.e., switching DE from HIGH to LOW, the
disable signal is passed directly across the barrier and
disables the output after a barrier transmission delay and
output disable time (tDLZ/tDHZ).
DE
D
tDZL
tDD tDD tDLZ
tDZH
tDHZ
Y
Z
FIGURE 1. ISO422 Data Transmit.
RECIEVE
The receive data is determined by the data bus differential
signal after a barrier transmission delay (tRZL). When the
difference between the A input and the B input (A-B) is
greater than +200mV, the R output will be HIGH. If A-B is
more negative than –200mV, the R output is undefined.
Since the reciver has a high impedance input, no disable
signal is required for the data bus input, which is always
active. The receive enable/disable time is simply the time to
enable/disable the R output (tRLZ) and does not require any
additional barrier transmission time.
RE
tRLZ
tRZH
tRZL
R
tRZH
tRLH
tRHL
A
B
FIGURE 2. ISO422 Data Receive.
DATA CORRUPTION
If, due to transient upset, the data passed across the barrier
is corrupted, the data will be restored within 100ns from the
end of the corrupting signal.
SYNCHRONIZATION
The data transmitted across the barrier is coded using an
internal clock. This clock also captures the incoming asyn-
chronous data and synchronizes it to the clock edges. This
will give rise to an rms propagation delay jitter of approxi-
mately 50ns.
LOOPBACK
A loopback function is provided by the LBE input. If this
input is HIGH, then enabling both the transmitter and the
receiver will cause the device to route the D input to the R
output, in addition to the data bus outputs. Data on the
incoming bus is ignored. This feature allows a simple con-
nection test to be performed during any application. When
LBE is LOW, transmit and receive will operate in the normal
full-duplex mode.
DATA BUS CONNECTION
ISO422 can be used in half duplex, or full duplex data
communication bus systems. It is capable of continuously
driving a 54Ω load, equivalent to a double-terminated trans-
mission line, at the fully specified data rate. When connect-
ing to the data bus, the voltage on the A and B input lines
must remain between VSB and GNDB. This can be achieved
by using a common bus ground connection, such as GNDB,
as shown in Figures 5 and 6.
For any system connected to the bus, the isolation provided
by ISO422 allows the independent local ground potential to
be as high as 1500Vrms with respect to the date bus ground
reference. This feature replaces the limited +12V to –7V
range of the RS-485 standard with the full-isolation voltage
capability of the ISO422.
®
5 ISO422
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet ISO422.PDF ] | |
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