LTC1387 Linear Technology, LTC1387 Datasheet - Page 10

• Manufacturer Part Number: LTC1387
• Description: Single 5V RS232/RS485 Multiprotocol Transceiver
• Manufacturer: Linear Technology

LTC1387
A
EMI and signal reflection problems. Slow slew rate sys-
tems can often use improperly terminated or even
unterminated cables with acceptable results. The RS485
differential input receiver features an offset input thresh-
old of – 80mV at 0V common mode voltage. This allows
the receiver output to have a known High output state
when the inputs are open or shorted. The receiver also
features an input hysteresis of 40mV. The charge pump
can be kept active regardless of the state of DXEN and
RXEN pins by keeping the ON pin High. This improves the
receiver response time by removing the 100 s charge
pump start-up time.
In RS232 mode, the drivers and receivers can be selected
from the Function Tables with control inputs ON, RXEN
and DXEN. The receivers feature a typical 0.6V input
hysteresis.
10
PPLICATI
O
U
S
I FOR ATIO
U
INTERFACE
TRANSMIT MODE
MODE = 0
RXEN = 0
DXEN = 1
Figure 13. Half-Duplex RS232 (1-Channel), Half-Duplex RS485
RS232
A
B
W
RS232
RECEIVE MODE
RS485
RS485
MODE = 0
RXEN = 1
DXEN = 0
RS232
U
A
B
Y
Z
TRANSMIT MODE
D
D
LTC1387
Y
Z
MODE = 1
RXEN = 0
DXEN = 1
RS485
All the interface driver outputs are fault protected by a
current limiting and thermal shutdown circuit. The thermal
shutdown circuit disables both the RS232 and RS485
driver outputs when the die temperature reaches 150 C.
The thermal shutdown circuit reenables the drivers when
the die temperature cools to 135 C.
A loopback mode enables internal connections from driver
outputs to receiver inputs for self-test. The driver outputs
are not isolated from the external loads during loopback.
The charge pump generates boosted positive voltage V
and negative voltage V
single 5V V
0.1 F capacitors.
R
R
A
B
R
R
D
D
ON
RXEN
DXEN
485/232
A
B
Y
Z
RECEIVE MODE
/SLEW
MODE = 1
RXEN = 1
DXEN = 0
RS485
V
CC
CC
supply. The charge pump requires four
DX/RX
CONTROLLER
RXEN
DXEN
MODE
SHUTDOWN
MODE = X
RXEN = 0
DXEN = 0
MODE
EE
1387 • F13
for true RS232 levels from a
DD