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PDF LTC2871 Data sheet ( Hoja de datos )
| Número de pieza | LTC2871 | |
| Descripción | RS232/RS485 Multiprotocol Transceivers | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n One RS485 and Two RS232 Transceivers
n 3V to 5.5V Supply Voltage
n 20Mbps RS485 and 500kbps RS232
n Automatic Selection of Integrated RS485 (120Ω)
and RS232 (5kΩ)Termination Resistors
n Half-/Full-Duplex RS485 Switching
n High ESD: ±26kV (LTC2870), ±16kV (LTC2871)
n Logic Loopback Mode
n 1.7V to 5.5V Logic Interface
n Supports Up to 256 RS485 Nodes
n RS485 Receiver Failsafe Eliminates UART Lockup
n Available in 28-Pin 4mm × 5mm QFN and
TSSOP (LTC2870), and 38-Pin 5mm × 7mm QFN
and TSSOP (LTC2871)
APPLICATIONS
n Flexible RS232/RS485/RS422 Interface
n Software Selectable Multiprotocol Interface Ports
n Point-of-Sale Terminals
n Cable Repeaters
n Protocol Translators
LTC2870/LTC2871
RS232/RS485 Multiprotocol
Transceivers with
Integrated Termination
DESCRIPTION
The LTC®2870/LTC2871 are robust pin-configurable mul-
tiprotocol transceivers, supporting RS232, RS485, and
RS422 protocols, operating on a single 3V to 5.5V supply.
The LTC2870 can be configured as two RS232 single-ended
transceivers or one RS485 differential transceiver on shared
I/O lines. The LTC2871 offers independent control of two
RS232 transceivers and one RS485 transceiver, each on
dedicated I/O lines.
Pin-controlled integrated termination resistors allow
for easy interface reconfiguration, eliminating external
resistors and control relays. Half-duplex switches allow
four-wire and two-wire RS485 configurations. Loopback
mode steers the driver inputs to the receiver outputs for
diagnostic self-test.The RS485 receivers support up to
256 nodes per bus, and feature full failsafe operation for
floating, shorted or terminated inputs.
An integrated DC/DC boost converter uses a small induc-
tor and one capacitor, eliminating the need for multiple
supplies for driving RS232 levels.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATIONS
Protocol Switching with
Automatic Termination Selection
1.7V TO VCC
3V TO 5.5V
RS232 RS485
VL
485/232
LTC2870
VCC
DY
Y
Z
DZ
www.DataSheet4U.com
RA
A
B
RB
Simultaneous Protocols and
RS485 Termination Switching
1.7V TO VCC
RS485
TERMINATION
OFF ON
VL
TE485
DI
RO
LTC2871
3V TO 5.5V
VCC
Y
120Ω
Z
A
120Ω
B
DIN1
DOUT1
ROUT1
RIN1
DIN2
DOUT2
ROUT2
RIN2
RS485 Duplex Switching
1.7V TO VCC
VL
LTC2870,
LTC2871
3V TO 5.5V
VCC
DI,
DY
RS485
FULL HALF
DUPLEX
H/F
RO,
RB
Y
Z
A
B
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1 page  
LTC2870/LTC2871
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
RTERM Terminating Resistor
TE485 = VL, A – B = 2V, B = –7V, 0V, 10V
(Figure 8) (Note 5)
l 108 120 156
Ω
RS232 Driver
VOLD
VOHD
Output Low Voltage
Output High Voltage
Three-State (High Impedance) Output Current
RL = 3kΩ; VEE ≤ –5.9V
RL = 3kΩ; VDD ≥ 6.5V
Y or Z (LTC2870) = ±15V
RS232 Receiver Enabled
DOUT1 or DOUT2 (LTC2871) = ±15V
l –5 –5.7 –7.5
l 5 6.2 7.5
l ±156
l ±10
V
V
μA
μA
Output Short-Circuit Current
Driver Output = 0V
l
±35 ±90
mA
RS232 Receiver
Input Threshold Voltage
l 0.6 1.5 2.5
V
Input Hysteresis
l 0.1 0.4 1.0
V
Output Low Voltage
Output High Voltage
Input Resistance
I(RA, RB, ROUT1, ROUT2) = 1mA (Sinking)
1.7V ≤ VL ≤ 5.5V
I(RA, RB, ROUT1, ROUT2) = –1mA (Sourcing)
1.7V ≤ VL ≤ 5.5V
–15V ≤ (A, B, RIN1, RIN2) ≤ 15V,
RS232 Receiver Enabled
l
l VL – 0.4
l3
5
0.4
7
V
V
kΩ
Three-State (High Impedance) Output Current
Output Short-Circuit Current
Logic Inputs
0V ≤ (RA, RB, ROUT1, ROUT2) ≤ VL
VL = 5.5V
0V ≤ (RA, RB, ROUT1, ROUT2) ≤ VL
l
0 ±5
μA
l
±25 ±50
mA
Threshold Voltage
Input Current
l 0.4
l
0.75 • VL
0 ±5
V
μA
Power Supply Generator
VDD Regulated VDD Output Voltage
RS232 Drivers Enabled, Outputs Loaded with
7V
VEE Regulated VEE Output Voltage
RL = 3kΩ to GND, DIN1/DY = VL, DIN2/DZ = 0V
(Note 3)
–6.3
V
ESD
LTC2870 Interface Pins (A, B, Y, Z)
Human Body Model to GND or VCC, Powered or
LTC2871 Interface Pins (A, B, Y, Z, RIN1, RIN2, Unpowered (Note 7)
DOUT1, DOUT2)
±26 kV
±16 kV
All Other Pins
Human Body Model (Note 7)
±4 kV
www.DataSheet4U.com
28701f
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5 Page 
BLOCK DIAGRAM
LTC2870
LTC2870/LTC2871
DXEN
RXEN
TE485
H/F
485/232
FEN
LB
DY
DZ
1.7V TO 5.5V
(≤ VCC)
0.1μF
VL
3V TO 5.5V
10μH
2.2μF
VCC
220nF
SW CAP
CONTROL
LOGIC
RT232
RT485
DRIVERS
PULSE-SKIPPING
BOOST
REGULATOR
f = 1.2MHz
232
RT485
485
120Ω
232
125k
125k
VDD
VEE 1μF
1μF
Y
Z
LOOPBACK
PATH
RA
RB
RECEIVERS
232
RT232
5k
485
232
5k
H/F
125k
RT485
A
125k
120Ω
B
www.DataSheet4U.com
GND
2870 BD
28701f
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11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC2871.PDF ] | |
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