FEATURES
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LTC2873
Single-Bus RS485/RS232
Multiprotocol Transceiver with
Switchable Termination
DESCRIPTION
The
LTC
®
2873
is a robust pin-configurable multiprotocol
transceiver that supports RS232, RS485, and RS422
protocols while operating on a single 3V to 5.5V supply.
The LTC2873 can be configured as a half-duplex RS485
transceiver or as an RS232 transceiver using the same
two bus pins.
A pin-controlled integrated termination resistor allows for
easy interface reconfiguration, eliminating external resis-
tors and control relays. Loopback mode steers the driver
inputs to the receiver outputs for diagnostic self-test.
The RS485 receiver supports up to 256 nodes per bus,
and features full failsafe operation for floating, shorted or
terminated inputs.
An integrated DC/DC boost converter uses a tiny
2mm × 1.6mm inductor and one capacitor, eliminating
the need for multiple supplies when driving RS232 levels.
All registered trademarks and trademarks are the property of their respective owners.
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One RS485 or One RS232 Transceiver
3V to 5.5V Supply Voltage
Up to 20Mbps RS485
Slew-Controlled RS232 Operation:
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Selectable 1Mbps or 250kbps
Automatic Selection of Integrated RS485 (120Ω)
and RS232 (5kΩ) Termination Resistors
High ESD:
±26kV
HBM
Logic Loopback Mode
1.7V to 5.5V Logic Interface
Supports Up to 256 RS485 Nodes
RS485 Receiver Failsafe Eliminates UART Lockup
H-Grade Available (–40°C to 125°C)
Available in 24-Pin 4mm × 5mm QFN Package
APPLICATIONS
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Software Selectable RS232/RS485/RS422 Interface
Industrial Sensors and Actuators
Alarm Systems
Traffic Control and Monitoring
Highway Signs and Jumbo Displays
TYPICAL APPLICATION
1.7V TO V
CC
1 F
V
L
SHDN
DATA IN
DI
LTC2873
RS485
A/DO
B/RI
V
DD
RS232
5k
V
EE
CAP
SW
V
CC
RS485
(485/232
HIGH)
RS232
(485/232
LOW)
220nF
10 H
3V TO 5.5V
2.2 F
RS485/RS232 Mode Switching
DI
485/232
5V/DIV
RS232
RS485
DATA OUT
485/232
D/R
(485)
RO
485/232
RE485
TE485
DE485/
F232
LB
GND
120
B/RI
1 F
A/DO
3V/DIV
1 F
1µs/DIV
2873 TA01
2873 TA01b
Document Feedback
For more information
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1
REV B
LTC2873
ABSOLUTE MAXIMUM RATINGS
(Notes 1 and 2)
PIN CONFIGURATION
TOP VIEW
TE485
GND
19 NC
18 V
CC
25
V
EE
17 A/DO
16 GND
15 B/RI
14 V
CC
8
GND
9 10 11 12
GND
CAP
V
EE
SW
13 V
DD
V
CC
Input Supplies
V
CC
, V
L
.................................................... –0.3V to 7V
Generated Supplies
V
DD
................................................ V
CC
– 0.3V to 7.5V
V
EE
......................................................... –7.5V to 0.3V
SW ............................................... –0.3V to (V
DD
+ 0.3V)
CAP ................................................. (V
EE
–
0.3V) to 0.3V
A/DO, B/RI ...................................................–15V to 15V
DI, 485/232, DE485/F232,
RE485,
TE485,
LB ................................................ –0.3V to 7V
SHDN,
RO .......................................–0.3V to (V
L
+ 0.3V)
Differential Terminator Voltage (Enabled)
(A/DO to B/RI) ..................................................... ±6V
Differential Terminator Voltage (Disabled)
(A/DO to B/RI) ................................................... ±30V
Operating Temperature
LTC2873C ............................................... 0°C to 70°C
LTC2873I .............................................–40°C to 85°C
LTC2873H .......................................... –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
LB
24 23 22 21 20
V
EE
1
RO 2
485/232 3
RE485
4
DE485/F232 5
DI 6
SHDN
7
UFD PACKAGE
24-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 150°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 25) IS V
EE
, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC2873CUFD#PBF
LTC2873IUFD#PBF
LTC2873HUFD#PBF
TAPE AND REEL
LTC2873CUFD#TRPBF
LTC2873IUFD#TRPBF
LTC2873HUFD#TRPBF
http://www.linear.com/product/LTC2873#orderinfo
PART MARKING
2873
2873
2873
PACKAGE DESCRIPTION
24-Lead (4mm × 5mm) Plastic QFN
24-Lead (4mm × 5mm) Plastic QFN
24-Lead (4mm × 5mm) Plastic QFN
TEMPERATURE RANGE
0°C to 70°C
–40°C
to 85°C
–40°C
to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
V
L
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REV B
For more information
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LTC2873
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
L
= 3.3V,
TE485
= V
L
, LB = 0V unless otherwise noted. (Notes 2, 6)
SYMBOL PARAMETER
Supplies
V
CC
V
L
Supply Voltage Operating Range
Logic Supply Voltage Operating Range
V
CC
Supply Current in Shutdown Mode
V
CC
Supply Current in RS232 Mode or
RS485 Mode, Driver and Receiver Enabled,
Termination Disabled
V
CC
Supply Current in RS485 Mode with
Receiver and Termination Enabled, Driver
Disabled
V
L
Supply Current in Any Mode
Power Supply Generator
V
DD
V
EE
|V
OD
|
Regulated V
DD
Output Voltage
Regulated V
EE
Output Voltage
Differential Output Voltage
SHDN
= V
L
, No Load
SHDN
= V
L
, No Load
R
L
= Open, V
CC
= 3V (Figure 1)
R
L
= 27Ω, V
CC
= 4.5V (Figure 1)
R
L
= 27Ω, V
CC
= 3V (Figure 1)
R
L
= 50Ω, V
CC
= 3.13V (Figure 1)
R
L
= 27Ω, V
CC
= 3V (Figure 1)
R
L
= 50Ω, V
CC
= 3.13V (Figure 1)
R
L
= 27Ω or 50Ω (Figure 1)
R
L
= 27Ω or 50Ω (Figure 1)
–7V ≤ V
OUT
≤ 12V (Figure 2)
(A/DO or B/RI) = 12V or –7V,
V
CC
= 0V or 3.3V (Figure 3)
(A/DO or B/RI) = 12V or –7V,
V
CC
= 0V or 3.3V (Figure 3)
–7V ≤ (A/DO or B/RI) ≤ 12V
B = 0V
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l
l
l
l
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
3
1.7
TYP
MAX
5.5
V
CC
UNITS
V
V
µA
mA
V
L
≤ V
CC
SHDN
= 0V
No Load,
SHDN
=
TE485
= DE485/F232 = V
L
RE485
= 0
No Load,
SHDN
= 485/232 = V
L
DE485/F232 =
RE485
=
TE485
= 0
No Load
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l
l
8
4
30
9
l
4
9
mA
l
0
7.0
–6.3
5
µA
V
V
RS485 Driver
2.1
1.5
2
V
CC
V
CC
V
CC
0.2
0.2
3
0.2
±250
–100
125
±200
220
–200
–70
40
Output Low, I(RO) = 3mA (Sinking),
3V ≤ V
L
≤ 5.5V
Output Low, I(RO) = 1mA (Sinking),
1.7V ≤ V
L
< 3V
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l
V
V
V
V
V
V
V
mA
µA
kΩ
mV
mV
∆|V
OD
|
V
OC
∆|V
OC
|
I
OSD485
I
IN485
R
IN485
Difference in Magnitude of Differential Output
Voltage for Complementary Output States
Common Mode Output Voltage
Difference in Magnitude of Common Mode Output
Voltage for Complementary Output States
Maximum Short-Circuit Current
Input Current (A/DO, B/RI)
Input Resistance (A/DO, B/RI)
Differential Input Signal Threshold
Voltage (A/DO to B/RI)
Input Hysteresis
Input DC Failsafe Hysteresis
RS485 Receiver
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125
Differential Input Failsafe Rising Threshold Voltage –7V ≤ (A/DO or B/RI) ≤ 12V, (A/D0 – B/RI) Rising
V
OL
Receiver Output Low Voltage
–20
0.4
0.4
mV
mV
V
V
For more information
www.analog.com
3
REV B
LTC2873
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
L
= 3.3V,
TE485
= V
L
, LB = 0V unless otherwise noted. (Notes 2, 6)
SYMBOL PARAMETER
V
OH
Receiver Output High Voltage
CONDITIONS
Output High, I(RO) = –3mA (Sourcing),
3V ≤ V
L
≤ 5.5V
Output High, I(RO) = –1mA (Sourcing),
1.7V ≤ V
L
< 3V
Three-State (High Impedance) Output Current (RO)
Short-Circuit Current (RO)
R
TERM
Terminating Resistor
0V ≤ RO ≤ V
L
, V
L
= 5.5V,
RE485
= V
L
0V ≤ RO ≤ V
L
, V
L
= 5.5V
TE485
= 0V, V
AB
= 2V,
V
B
= –7V, 0V, 10V (Figure 8)
R
L
= 3kΩ, V
EE
≤ –6V
R
L
= 3kΩ, V
DD
≥ 6.5V
Driver Output = 0V
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l
l
ELECTRICAL CHARACTERISTICS
MIN
V
L
– 0.4
V
L
– 0.4
TYP
MAX
UNITS
V
V
0
108
120
±5
±135
156
µA
mA
Ω
RS232 Driver
V
OLD
V
OHD
Output Low Voltage
Output High Voltage
Output Short-Circuit Current
RS232 Receiver
Input Threshold Voltage
Input Hysteresis
Output Low Voltage
Output High Voltage
Input Resistance
Output Short-Circuit Current
Logic Inputs
Threshold Voltage
Input Current
ESD
Interface Pins (A/DO, B/RI)
All Other Pins
Human Body Model to GND or V
CC
, Powered
or Unpowered (Note 5)
Human Body Model (Note 5)
±26
±4
kV
kV
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l
l
l
l
l
–5
5
–5.5
5.9
±25
V
EE
V
DD
±90
2.5
1.0
0.4
V
V
mA
V
V
V
V
kΩ
mA
V
µA
0.6
0.1
V
L
– 0.4
3
1.5
0.4
I(RO) = 1mA (Sinking), 1.7V ≤ V
L
< 5.5V
I(RO) = –1mA (Sourcing), 1.7V ≤ V
L
< 5.5V
–15V ≤ B/RI ≤ 15V, 485/232 = 0V
V
L
= 5.5V, 0V ≤ RO ≤ V
L
l
l
l
l
5
±25
7
±50
0.75 • V
L
0.4
0
±5
4
REV B
For more information
www.analog.com
LTC2873
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
L
= 3.3V,
TE485
= V
L
, LB = 0V unless otherwise noted. (Notes 2, 6)
SYMBOL
PARAMETER
Maximum Data Rate
t
PLHD485
, t
PHLD485
Driver Propagation Delay
Driver Propagation Delay Difference
R
DIFF
= 54Ω, C
L
= 100pF (Figure 4)
t
PLHD485
– t
PHLD485
t
SKEWD485
t
RD485
, t
FD485
t
ZLD485
, t
ZHD485
,
t
LZD485
, t
HZD485
t
ZHSD485
, t
ZLSD485
t
HZSD485
, t
LZSD485
t
PLHR485
, t
PHLR485
t
SKEWR485
t
RR485
, t
FR485
t
ZLR485
, t
ZHR485
,
t
LZR485
, t
HZR485
t
ZHSR485
, t
ZLSR485
t
HZSR485
, t
LZSR485
t
RTEN485
, t
RTZ485
Driver Skew (A/DO to B/RI)
Driver Rise or Fall Time
Driver Output Enable or Disable Time
Driver Enable from Shutdown Time
(Note 7)
Driver Output Disable Into
Shutdown Time
Receiver Input to Output Time
Differential Receiver Skew
t
PLHR485
– t
PHLR485
Receiver Output Rise or Fall Time
Receiver Output Enable or
Disable Time
Receiver Enable from Shutdown Time
(Note 7)
Receiver Output Disable Into
Shutdown Time
Termination Enable or Disable
Time
Maximum Data Rate (Figure 15)
R
DIFF
= 54Ω, C
L
= 100pF (Figure 4)
R
DIFF
= 54Ω, C
L
= 100pF (Figure 4)
SHDN
= V
L
, R
L
= 500Ω, C
L
= 50pF,
DE485
↑
and
↓
(Figure 5)
DE485/F232 = V
L
, R
L
= 500Ω,
C
L
= 50pF,
SHDN
↑
(Figure 5)
DE485/F232 = V
L
, R
L
= 500Ω,
C
L
= 50pF,
SHDN
↓
(Figure 5)
C
L
= 15pF, V
CM
= 1.5V,
|A/DO to B/RI| = 1.5V, (Figure 6)
C
L
= 15pF (Figure 6)
C
L
= 15pF (Figure 6)
485/232 =
SHDN
= V
L
, R
L
= 1kΩ,
C
L
= 15pF,
RE485
↓
and
↑
(Figure 7)
485/232 = V
L
,
RE485
= 0V, R
L
= 1kΩ,
C
L
= 15pF ,
SHDN
↑
(Figure 7)
485/232 = V
L
,
RE485
= 0V, R
L
= 1kΩ,
C
L
= 15pF ,SHDN
↓
(Figure 7)
485/232 = V
L
,
SHDN
= V
L
, B = 0,
(A/DO to B/RI) = 2V (Figure 8)
R
L
= 3kΩ, C
L
= 2.5nF, (Fast, Slow Modes)
R
L
= 3kΩ, C
L
= 1nF, (Fast, Slow Modes)
R
L
= 3kΩ, C
L
= 0.25nF, (Fast Mode)
R
L
= 3kΩ, C
L
= 2.5nF, (Fast, Slow Modes)
R
L
= 3kΩ, C
L
= 50pF, (Slow Mode)
R
L
= 3kΩ, C
L
= 50pF, (Fast Mode)
R
L
= 3kΩ, C
L
= 50pF, (Slow Mode)
R
L
= 3kΩ, C
L
= 50pF, (Fast Mode)
R
L
= 3kΩ, C
L
= 50pF, (Slow Mode)
R
L
= 3kΩ, C
L
= 50pF, (Fast Mode)
V
DD
= 7.0V, V
EE
= –6.3V, 485/232 = 0V,
R
L
= 3kΩ, C
L
= 50pF,
SHDN
↑
(Figure 10)
485/232 = 0V, R
L
= 3kΩ, C
L
= 50pF,
SHDN
↓
(Figure 10)
C
L
= 150pF (Figure 11)
C
L
= 150pF (Figure 11)
C
L
= 150pF (Figure 11)
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l
l
l
l
SWITCHING CHARACTERISTICS
RS485 Switching Characteristics
CONDITIONS
(Note 3) (Figure 15)
R
DIFF
= 54Ω, C
L
= 100pF (Figure 4)
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l
MIN
20
TYP
MAX
UNITS
Mbps
20
0
0
7.5
70
±6
±8
12.5
120
ns
ns
ns
ns
ns
µs
μs
ns
ns
ns
ns
µs
µs
µs
4
0.5
45
0
3
12
4
0.5
12
1
85
±9
15
85
12
1
100
RS232 Switching Characteristics
l
l
l
l
l
l
l
l
100
250
1000
2
30
150
1.5
0.4
0
0
5
0.6
60
25
70
200
3
1
±400
±100
12
2
200
kbps
kbps
kbps
V/µs
V/µs
V/µs
µs
µs
ns
ns
µs
µs
ns
ns
ns
Driver Slew Rate (Figure 9)
t
PHLD232
, t
PLHD232
t
SKEWD232
t
ZLSD232
, t
ZHSD232
t
LZSD232
, t
HZSD232
t
PHLR232
, t
PLHR232
t
SKEWR232
t
RR232
, t
FR232
Driver Propagation Delay (Figure 9)
Driver Skew (Figure 9)
Driver Enable from Shutdown
Time (Figure 7)
Driver Output Disable into
Shutdown Time
Receiver Propagation Delay
Receiver Skew
Receiver Output Rise or Fall Time
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REV B
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