LTC2854/LTC2855
3.3V 20Mbps RS485/RS422
Transceivers with Integrated
Switchable Termination
FEATURES
DESCRIPTION
Integrated, Logic-Selectable 120Ω Termination Resistor
nn 3.3V Supply Voltage
nn 20Mbps Maximum Data Rate
nn No Damage or Latchup Up to ±25kV HBM
nn High Input Impedance Supports 256 Nodes (C-, I‑Grade)
nn Operation Up to 125°C (H-Grade)
nn Guaranteed Failsafe Receiver Operation Over the
Entire Common Mode Range
nn Current Limited Drivers and Thermal Shutdown
nn Delayed Micropower Shutdown: 5µA Maximum (C-, I-Grade)
nn Power Up/Down Glitch-Free Driver Outputs
nn Low Operating Current: 370µA Typical in Receive Mode
nn Compatible with TIA/EIA-485-A Specifications
nn Available in 10-Pin 3mm × 3mm DFN, 12-Pin
4mm × 3mm DFN and 16-Pin SSOP Packages
The LTC®2854 and LTC2855 are low power, 20Mbps
RS485/RS422 transceivers operating on 3.3V supplies.
The receiver includes a logic-selectable 120Ω termination,
one-eighth unit load supporting up to 256 nodes per bus
(C-, I-Grade), and a failsafe feature that guarantees a high
output state under conditions of floating or shorted inputs.
nn
APPLICATIONS
The driver maintains a high output impedance over the
entire common mode range when disabled or when the
supply is removed. Excessive power dissipation caused by
bus contention or a fault is prevented by current limiting
all outputs and by a thermal shutdown.
Enhanced ESD protection allows the LTC2854 to withstand
±25kV (human body model) and the LTC2855 to withstand
±15kV on the transceiver interface pins without latchup
or damage.
PRODUCT SELECTION GUIDE
Low Power RS485/RS422 Transceiver
Level Translator
nn Backplane Transceiver
nn
nn
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.
PART NUMBER
DUPLEX
PACKAGE
LTC2854
HALF
DFN-10
LTC2855
FULL
SSOP-16, DFN-12
TYPICAL APPLICATION
DE
DI
R
R
RO
RE
TE
LTC2854 at 20Mbps into 54Ω
LTC2854
LTC2854
120Ω
120Ω
D
D
RO
RE
TE
DI
DE
A
B
DI
2V/DIV
LTC2854
A-B
285455 TA01
120Ω
20ns/DIV
R
285455 TA01b
D
RO RE TE DE
DI
285455fc
For more information www.linear.com/LTC2854
1
LTC2854/LTC2855
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (VCC).................................... –0.3V to 7V
Logic Input Voltages (RE, DE, DI, TE)............. –0.3V to 7V
Interface I/O:
A, B, Y, Z........................................(VCC –15V) to +15V
(A-B) or (B-A) with Terminator Enabled...................6V
Receiver Output Voltage (RO).........–0.3V to (VCC +0.3V)
Operating Temperature (Note 4)
LTC2854C, LTC2855C............................... 0°C to 70°C
LTC2854I, LTC2855I.............................–40°C to 85°C
LTC2854H, LTC2855H........................ –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
GN Package....................................................... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
TOP VIEW
10 VCC
9 B
RO
1
RE
2
DE
3
DI
4
7 NC
TE
5
6 GND
11
8 A
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
EXPOSED PAD (PIN 11) PCB GND CONNECTION
TJMAX = 150°C, θJA = 43°C/W
θJC = 2.96°C/W
RO
1
12 VCC
RE
2
11 A
DE
3
DI
4
9
Z
TE
5
8
Y
GND
6
7
NC
13
10 B
DE PACKAGE
12-LEAD (4mm × 3mm) PLASTIC DFN
EXPOSED PAD (PIN 13) PCB GND CONNECTION
TJMAX = 150°C, θJA = 44°C/W
θJC = 4.3°C/W
RO
1
16 VCC
RE
2
15 A
DE
3
14 B
DI
4
13 Z
TE
5
12 Y
GND
6
11 NC
NC
7
10 NC
NC
8
9
NC
GN PACKAGE
16-LEAD (NARROW 0.150) PLASTIC SSOP
TJMAX = 150°C, θJA = 110°C/W
θJC = 40°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2854CDD#PBF
LTC2854CDD#TRPBF
LCQG
10-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2854IDD#PBF
LTC2854IDD#TRPBF
LCQG
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2854HDD#PBF
LTC2854HDD#TRPBF
LCQG
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LTC2855CDE#PBF
LTC2855CDE#TRPBF
2855
12-Lead (4mm × 3mm) Plastic DFN
0°C to 70°C
LTC2855IDE#PBF
LTC2855IDE#TRPBF
2855
12-Lead (4mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2855HDE#PBF
LTC2855HDE#TRPBF
2855
12-Lead (4mm × 3mm) Plastic DFN
–40°C to 125°C
LTC2855CGN#PBF
LTC2855CGN#TRPBF
2855
16-Lead (Narrow 0.150) Plastic SSOP
0°C to 70°C
LTC2855IGN#PBF
LTC2855IGN#TRPBF
2855I
16-Lead (Narrow 0.150) Plastic SSOP
–40°C to 85°C
LTC2855HGN#PBF
LTC2855HGN#TRPBF
2855H
16-Lead (Narrow 0.150) Plastic SSOP
–40°C to 125°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2854CDD
LTC2854CDD#TR
LCQG
10-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2854IDD
LTC2854IDD#TR
LCQG
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2854HDD
LTC2854HDD#TR
LCQG
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LTC2855CDE
LTC2855CDE#TR
2855
12-Lead (4mm × 3mm) Plastic DFN
0°C to 70°C
LTC2855IDE
LTC2855IDE#TR
2855
12-Lead (4mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2855HDE
LTC2855HDE#TR
2855
12-Lead (4mm × 3mm) Plastic DFN
–40°C to 125°C
LTC2855CGN
LTC2855CGN#TR
2855
16-Lead (Narrow 0.150) Plastic SSOP
0°C to 70°C
LTC2855IGN
LTC2855IGN#TR
2855I
16-Lead (Narrow 0.150) Plastic SSOP
–40°C to 85°C
LTC2855HGN
LTC2855HGN#TR
2855H
16-Lead (Narrow 0.150) Plastic SSOP
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/
2
285455fc
For more information www.linear.com/LTC2854
LTC2854/LTC2855
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V unless otherwise noted (Note 2).
SYMBOL
PARAMETER
CONDITIONS
MIN
|VOD|
Differential Driver Output Voltage
R = ∞, VCC = 3V (Figure 1)
R = 27Ω, VCC = 3V (Figure 1)
R = 50Ω, VCC = 3.13V (Figure 1)
l
l
l
D|VOD|
Change in Magnitude of Driver
Differential Output Voltage for
Complementary Output States
R = 27Ω or R = 50Ω (Figure 1)
l
TYP
MAX
UNITS
VCC
VCC
VCC
V
V
V
0.2
V
Driver
1.5
2
VOC
Driver Common Mode Output Voltage
R = 27Ω or R = 50Ω (Figure 1)
l
3
V
D|VOC|
Change in Magnitude of Driver
Common Mode Output Voltage for
Complementary Output States
R = 27Ω or R = 50Ω (Figure 1)
l
0.2
V
IOZD
Driver Three-State (High Impedance)
Output Current on Y and Z
DE = OV, (Y or Z) = –7V, 12V (LTC2855)
H-Grade
l
l
±10
±50
µA
µA
IOSD
Maximum Driver Short-Circuit Current
–7V ≤ (Y or Z) ≤ 12V (Figure 2)
±250
300
mA
mA
125
µA
l
–250
180
Receiver
IIN
RIN
Receiver Input Current (A, B)
Receiver Input Resistance
DE = TE = 0V, VCC = 0V or 3.3V, VIN = 12V
(Figure 3) (C-, I-Grade)
DE = TE = 0V, VCC = 0V or 3.3V, VIN = –7V,
(Figure 3) (C-, I-Grade)
l
DE = TE = 0V, VCC = 0V or 3.3V, VIN = 12V
(Figure 3) (H-Grade)
DE = TE = 0V, VCC = 0V or 3.3V, VIN = –7V,
(Figure 3) (H-Grade)
l
l
–145
RE = VCC or 0V, DE = TE = 0V,
VIN = –7V, –3V, 3V, 7V, 12V (Figure 3)
(C-, I-Grade)
l
96
125
kΩ
RE = VCC or 0V, DE = TE = 0V,
VIN = –7V, –3V, 3V, 7V, 12V (Figure 3)
(H-Grade)
l
48
125
kΩ
l
l
–100
µA
250
µA
µA
VTH
Receiver Differential Input Threshold
Voltage
–7V ≤ B ≤ 12V
±0.2
DVTH
Receiver Input Hysteresis
B = 0V
VOH
Receiver Output HIGH Voltage
I(RO) = –4mA, A-B = 200mV, VCC = 3V
l
VOL
Receiver Output LOW Voltage
I(RO) = 4mA, A-B = –200mV, VCC = 3V
l
0.4
V
IOZR
Receiver Three-State (High Impedance)
Output Current on RO
RE = VCC, 0V ≤ RO ≤ VCC
l
±1
µA
IOSR
Receiver Short-Circuit Current
0V ≤ RO ≤ VCC
l
±85
mA
RTERM
Receiver Input Terminating Resistor
TE = VCC, VAB = 2V, VB = –7V, 0V, 10V
(Figure 8)
l
108
156
Ω
VIH
Logic Input High Voltage
VCC = 3.6V
l
2
VIL
Logic Input Low Voltage
VCC = 3V
l
IINL
Logic Input Current
25
V
mV
2.4
V
120
Logic
V
0.8
V
l
0
±10
µA
DE = 0V, RE = VCC, TE = 0V
(C-, I-Grade)
(H-Grade)
l
l
0
0
5
15
µA
µA
DE = 0V, RE = 0V, TE = 0V
l
370
900
µA
Supplies
ICCS
ICCR
Supply Current in Shutdown Mode
Supply Current in Receive Mode
285455fc
For more information www.linear.com/LTC2854
3
LTC2854/LTC2855
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, TE = 0V unless otherwise noted (Note 2).
SYMBOL
PARAMETER
CONDITIONS
TYP
MAX
UNITS
ICCT
Supply Current in Transmit Mode
No Load, DE = VCC, RE = VCC, TE = 0V
l
MIN
450
1000
µA
ICCTR
Supply Current with Both Driver and
Receiver Enabled
No Load, DE = VCC, RE = 0V, TE = 0V
l
450
1000
µA
ICCTERM
Supply Current in Termination Mode
DE = 0V, RE = VCC, TE = VCC
l
110
180
µA
ICCTERMR
Supply Current in Receive and
Termination Mode
DE = 0V, RE = 0V, TE = VCC
l
450
950
µA
ICCTERMT
Supply Current in Transmit and
Termination Mode
DE = VCC, RE = VCC, TE = VCC
l
470
1000
µA
ICCTERMTR
Supply Current with Driver, Receiver
and Termination Enabled
DE = VCC, RE = 0V, TE = VCC
l
470
1000
µA
ESD Protection for RS485/RS422 Pins
A, B on LTC2854, Human Body Model
Y, Z, A, B on LTC2855, Human Body Model
ESD Protection
±25
±15
kV
kV
SWITCHING
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, TE = 0V unless otherwise noted (Note 2).
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Driver
fMAX
Maximum Data Rate
Note 3
l
tPLHD, tPHLD
Driver Input to Output
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
10
50
ns
DtPD
Driver Input to Output Difference
|tPLHD-tPHLD|
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
1
6
ns
20
Mbps
tSKEWD
Driver Output Y to Output Z
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
1
±6
ns
tRD, tFD
Driver Rise or Fall Time
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
4
12.5
ns
tZLD, tZHD, tLZD, tHZD Driver Enable or Disable Time
RL = 500Ω, CL = 50pF, RE = 0 (Figure 5)
l
70
ns
tZHSD, tZLSD
Driver Enable from Shutdown
RL = 500Ω, CL = 50pF, RE = VCC (Figure 5)
l
8
µs
tSHDN
Time to Shutdown
RL = 500Ω, CL = 50pF
(DE = ↓, RE = VCC) or (DE = 0, RE ↑)
(Figure 5)
l
100
ns
tPLHR, tPHLR
Receiver Input to Output
CL = 15pF, VCM = 1.5V, |VAB| = 1.5V, tR and
tF < 4ns (Figure 6)
l
50
70
ns
tSKEWR
Differential Receiver Skew
|tPLHR-tPHLR|
CL = 15pF (Figure 6)
l
1
6
ns
tRR, tFR
Receiver Output Rise or Fall Time
3
12.5
ns
50
ns
Receiver
CL = 15pF (Figure 6)
l
tZLR, tZHR, tLZR, tHZR Receiver Enable/Disable
RL = 1k, CL =15pF, DE = VCC (Figure 7)
l
tZHSR, tZLSR
Receiver Enable from Shutdown
RL = 1k, CL = 15pF, DE = 0V (Figure 7)
l
8
µs
tRTEN, tRTZ
Termination Enable or Disable Time
VB = 0V, VAB = 2V, RE = VCC, DE = 0V
(Figure 8)
l
100
µs
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime. High temperatures degrade operating lifetimes.
Operating lifetime is derated at temperatures greater than 105°C.
Note 2: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
4
Note 3: Maximum data rate is guaranteed by other measured parameters
and is not tested directly.
Note 4: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions.
Overtemperature protection activates at a junction temperature exceeding
150°C. Continuous operation above the specified maximum operating
junction temperature may result in device degradation or failure.
285455fc
For more information www.linear.com/LTC2854
LTC2854/LTC2855
TEST CIRCUITS
Y
GND
DI
OR
VCC
DRIVER
Z
Y
R
+
VOD
–
R
IOSD
GND
OR
DI
VCC
+
VOC
–
DRIVER
Z
+
–
–7V to +12V
285455 F01-2
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
IIN
VIN
+
–
A OR B
B OR A
RECEIVER
285455 F03
V
RIN = IN
IIN
Figure 3. Receiver Input Current and Input Resistance
DI
Y
DI
VCC
tPLHD
0V
tPHLD
CL
DRIVER
RDIFF
tSKEWD
VO
Y, Z
1/2 VO
CL
Z
90%
285455 F04a
Y-Z
10%
0
0
90%
10%
tFD
tRD
285455 F04b
Figure 4. Driver Timing Measurement
RL
Y
VCC
OR
GND
DI
CL
GND
OR
VCC
RL
Z
CL
VCC
OR
GND
VCC
1/2 VCC
0V
Y OR Z
DRIVER
DE
DE
VCC
VOL
Z OR Y
tZLD,
tZLSD
VO
1/2 VCC
VOH
0V
285455 F05a
tLZD
0.5V
0.5V
1/2 VCC
tZHD,
tZHSD
tHZD,
tSHDN
285455 F05b
Figure 5. Driver Enable and Disable Timing Measurements
285455fc
For more information www.linear.com/LTC2854
5
LTC2854/LTC2855
TEST CIRCUITS
A
±VAB/2
VCM
B
±VAB/2
tR
VAB
A-B
–VAB
RO
RECEIVER
CL
RO
285455 F06a
tF
90%
0
10%
90%
10%
tPLHR
VCC
90%
1/2 VCC
10%
VO
0
tPHLR
1/2 VCC
90%
10%
tRR
tFR
tSKEWR = tPLHR – tPHLR
285455 F06b
Figure 6. Receiver Propagation Delay Measurements
RE
VCC
1/2 VCC
0V
0V OR VCC
VCC OR 0V
tZLR,
tZLSR
A
B
RECEIVER
RL
RO
CL
RE
VCC
OR
GND
RO
VOL
RO
DI = 0V OR VCC
VCC
tLZR
VO
1/2 VCC
VOH
0.5V
1/2 VCC
0V
285455 F07a
0.5V
tZHR,
tZHSR
285455 F07b
tHZR
Figure 7. Receiver Enable and Disable Timing Measurements
RTERM = VAB
IA
IA
RO
A
RECEIVER
TE
B
+
–
TE
VAB
VCC
1/2 VCC
0V
IA
+
–
tRTEN
90%
tRTZ
10%
VB
285455 F08
Figure 8. Termination Resistance and Timing Measurements
6
285455fc
For more information www.linear.com/LTC2854
LTC2854/LTC2855
TYPICAL PERFORMANCE CHARACTERISTICS
Receiver Skew
vs Temperature
Driver Propagation Delay
vs Temperature
Driver Skew vs Temperature
VAB = 1.5V
CL = 15pF
0
16
PROP DELAY (ns)
1
18
RDIFF = 54Ω
CL = 100pF
1
DRIVER SKEW (ns)
RECEIVER SKEW (ns)
2
TA = 25°C, VCC = 3.3V, unless otherwise noted.
0
–1
–1
–40 –20
0
20
40
60
80
100 120
RDIFF = 54Ω
CL = 100pF
14
12
10
9
6
–40 –20
0
20
40
60
80
4
–40 –20
100 120
0
TEMPERATURE (˚C)
TEMPERATURE (˚C)
20
40
60
80
285455 G02
285455 G01
285455 G03
Driver Output Low/High Voltage
vs Output Current
RTERM vs Temperature
100 120
TEMPERATURE (˚C)
Driver Differential Output Voltage
vs Temperature
135
3
120
115
110
2
VOL
1
RDIFF = ∞
3
VOH
OUTPUT VOLTAGE (V)
125
OUTPUT VOLTAGE (V)
RESISTANCE (Ω)
130
RDIFF = 100Ω
RDIFF = 54Ω
2
1
105
100
–40 –20
0
20
40
60
80
0
100 120
0
20
10
TEMPERATURE (˚C)
30
40
50
65
PROP DELAY (ns)
OUTPUT VOLTAGE (V)
1
2
3
4
5
6
VAB = 1.5V
CL = 15pF
285455 G07
80
60
55
50
45
35
–40 –20
CL = 100pF
RDIFF = 54Ω
40
30
RDIFF = 100Ω
20
10
0
100 120
50
20
40
60
80
100 120
TEMPERATURE (˚C)
OUTPUT CURRENT (mA)
60
Supply Current vs Data Rate
60
40
SINK
40
285455 G06
SUPPLY CURRENT (mA)
SOURCE
3
2
20
TEMPERATURE (˚C)
Receiver Propagation Delay
vs Temperature
70
1
0
285455 G05
Receiver Output Voltage vs
Output Current (Source and Sink)
0
0
–40 –20
70
OUTPUT CURRENT (mA)
285455 G04
0
60
285455 G08
0
RDIFF = ∞
0.1
1
10
DATA RATE (Mbps)
100
285455 G09
285455fc
For more information www.linear.com/LTC2854
7
LTC2854/LTC2855
PIN FUNCTIONS
(DD/DE/GN)
RO (Pin 1): Receiver Output. If the receiver output is enabled (RE low) and A > B by 200mV, then RO will be high.
If A < B by 200mV, then RO will be low. If the receiver
inputs are open, shorted, or terminated without a signal,
RO will be high.
RE (Pin 2): Receiver Enable. A low enables the receiver.
A high input forces the receiver output into a high impedance state.
DE (Pin 3): Driver Enable. A high on DE enables the driver.
A low input will force the driver outputs into a high impedance. If RE is high with DE and TE low, the part will enter
a low power shutdown state.
DI (Pin 4): Driver Input. If the driver outputs are enabled
(DE high), then a low on DI forces the driver positive output low and negative output high. A high on DI, with the
driver outputs enabled, forces the driver positive output
high and negative output low.
8
TE (Pin 5): Internal Termination Resistance Enable. A high
input will connect a termination resistor (120Ω typical)
between pins A and B.
GND (Pins 6,11/6,13/6): Ground. Pins 11 and 13 are
backside thermal pad, connected to Ground.
Y (Pins NA/8/12): Positive Driver Output for LTC2855.
Z (Pins NA/9/13): Negative Driver Output for LTC2855.
B (Pins 9/10/14): Negative Receiver Input (and Negative
Driver Output for LTC2854).
A (Pins 8/11/15): Positive Receiver Input (and Positive
Driver Output for LTC2854).
VCC (Pins 10/12/16): Positive Supply. VCC = 3.0V < VCC <
3.6V. Bypass with 0.1µF ceramic capacitor.
285455fc
For more information www.linear.com/LTC2854
LTC2854/LTC2855
FUNCTION TABLES
LTC2854
LOGIC INPUTS
DE
RE
TE
MODE
A, B
RO
TERMINATOR
0
0
0
RECEIVE
RIN
DRIVEN
OFF
0
0
1
RECEIVE WITH TERM
RTERM
DRIVEN
ON
0
1
0
SHUTDOWN
RIN
HIGH-Z
OFF
0
1
1
TERM ONLY
RTERM
HIGH-Z
ON
1
0
0
TRANSMIT WITH RECEIVE
DRIVEN
DRIVEN
OFF
1
0
1
TRANSMIT WITH RECEIVE
AND TERM
DRIVEN
DRIVEN
ON
1
1
0
TRANSMIT
DRIVEN
HIGH-Z
OFF
1
1
1
TRANSMIT WITH TERM
DRIVEN
HIGH-Z
ON
LTC2855
LOGIC INPUTS
DE
RE
TE
MODE
A, B
Y, Z
RO
TERMINATOR
0
0
0
RECEIVE
RIN
HIGH-Z
DRIVEN
OFF
0
0
1
RECEIVE WITH TERM
RTERM
HIGH-Z
DRIVEN
ON
0
1
0
SHUTDOWN
RIN
HIGH-Z
HIGH-Z
OFF
0
1
1
TERM ONLY
RTERM
HIGH-Z
HIGH-Z
ON
1
0
0
TRANSMIT WITH RECEIVE
RIN
DRIVEN
DRIVEN
OFF
1
0
1
TRANSMIT WITH RECEIVE
AND TERM
RTERM
DRIVEN
DRIVEN
ON
1
1
0
TRANSMIT
RIN
DRIVEN
HIGH-Z
OFF
1
1
1
TRANSMIT WITH TERM
RTERM
DRIVEN
HIGH-Z
ON
BLOCK DIAGRAMS
RE
DE
LTC2854
LTC2855
VCC
VCC
SLEEP/SHUTDOWN
LOGIC AND DELAY
120Ω
RTERM
125k
RIN
RO
RE
DE
SLEEP/SHUTDOWN
LOGIC AND DELAY
TE
125k
RIN
RO
RECEIVER
B
25kV
B
(15kV)
125k
RIN
DI
DRIVER
A
(15kV)
120Ω
RTERM
TE
RECEIVER
125k
RIN
DI
A
25kV
Z
(15kV)
DRIVER
Y
(15kV)
GND
GND
285455 BD
285455fc
For more information www.linear.com/LTC2854
9
LTC2854/LTC2855
APPLICATIONS INFORMATION
Driver
The driver provides full RS485/RS422 compatibility. When
enabled, if DI is high, Y-Z is positive for the full-duplex
device (LTC2855) and A-B is positive for the half-duplex
device (LTC2854).
When the driver is disabled, both outputs are highimpedance. For the full-duplex LTC2855, the leakage on
the driver output pins is guaranteed to be less than 10µA
over the entire common mode range of –7V to +12V. On
the half-duplex LTC2854, the impedance is dominated by
the receiver input resistance, RIN.
Driver Overvoltage and Overcurrent Protection
The driver outputs are protected from short-circuits to
any voltage within the Absolute Maximum range of (VCC
–15V) to +15V. The typical peak current in this condition
does not exceed 180mA.
If a high driver output is shorted to a voltage just above
VCC , a reverse current will flow into the supply. When this
voltage exceeds VCC by about 1.4V, the reverse current
turns off. Preventing the driver from turning off with outputs
shorted to output voltages just above VCC keeps the driver
active even for receiver loads that have a positive common
mode with respect to the driver — a valid condition.
The worst-case peak reverse short-circuit current can be as
high as 300mA in extreme cold conditions. If this current
cannot be absorbed by the supply, a 3.6V Zener diode can
be added in parallel with the supply to sink this current.
the inputs are either shorted, left open, or terminated
(externally or internally), but not driven. This failsafe feature is guaranteed to work for inputs spanning the entire
common mode range of –7V to +12V.
The receiver output is internally driven high (to VCC) or
low (to ground) with no external pull-up needed. When the
receiver is disabled the RO pin becomes High-Z with leakage of less than ±1µA for voltages within the supply range.
Receiver Input Resistance
The receiver input resistance from A or B to ground is guaranteed to be greater than 96k (C-, I-Grade) when the termination is disabled. This is 8X higher than the requirements
for the RS485 standard and thus this receiver represents a
one-eighth unit load. This, in turn, means that 8X the
standard number of receivers, or 256 total, can be connected to a line without loading it beyond what is called
out in the RS485 standard. The receiver input resistance
from A or B to ground on high temperature H-Grade parts
is greater than 48k providing a one-quarter unit load. The
input resistance of the receivers is unaffected by enabling/
disabling the receiver and by powering/unpowering the
part. The equivalent input resistance looking into A and B
is shown in Figure 9. The termination resistor cannot be
enabled by TE if the device is unpowered or in thermal
shutdown mode.
>96kΩ
A
60Ω
All devices also feature thermal shutdown protection that
disables the driver and receiver in case of excessive power
dissipation (see Note 4).
TE
60Ω
>96kΩ
Receiver and Failsafe
285455 F09
With the receiver enabled, when the absolute value of the
differential voltage between the A and B pins is greater than
200mV, the state of RO will reflect the polarity of (A-B).
B
Figure 9. Equivalent Input Resistance into A and B
(on the LTC2854, Valid if Driver is Disabled)
The LTC2854/LTC2855 have a failsafe feature that guarantees the receiver output to be in a logic-high state when
10
285455fc
For more information www.linear.com/LTC2854
LTC2854/LTC2855
APPLICATIONS INFORMATION
When the TE pin is high, the termination resistor is enabled and the differential resistance from A to B is 120Ω.
Figure 10 shows the I/V characteristics between pins A
and B with the termination resistor enabled and disabled.
The resistance is maintained over the entire RS485 common mode range of –7V to +12V as shown in Figure 11.
Switchable Termination
Proper cable termination is very important for good signal
fidelity. If the cable is not terminated with its characteristic
impedance, reflections will result in distorted waveforms.
The LTC2854/LTC2855 are the first 3.3V RS485/RS422
transceivers to offer integrated switchable termination
resistors on the receiver input pins. This provides the
advantage of being able to easily change, through logic
control, the line termination for optimal performance when
configuring transceiver networks.
The integrated termination resistor has a high frequency
response which does not limit performance at the maximum specified data rate. Figure 12 shows the magnitude
and phase of the termination impedance vs frequency.
150
VAB = 2V
RESISTANCE (Ω)
140
130
120
110
100
–10
–5
5
10
0
COMMON MODE VOLTAGE (V)
Figure 10. Curve Trace Between A and B
with Termination Enabled and Disabled
15
285455 F11
Figure 11. Typical Resistance of the Enabled
Terminator vs Voltage on B Pin
30
185
15
PHASE
155
0
–15
140
MAGNITUDE
125
–30
110
–45
95
–60
80
10–1
100
FREQUENCY (MHz)
PHASE (°)
MAGNITUDE (Ω)
170
–75
101
285455 F12
Figure 12. Termination Magnitude
and Phase vs Frequency
285455fc
For more information www.linear.com/LTC2854
11
LTC2854/LTC2855
APPLICATIONS INFORMATION
Supply Current
The unloaded static supply currents in the LTC2854/
LTC2855 are very low —typically under 500µA for all modes
of operation. In applications with resistively terminated
cables, the supply current is dominated by the driver load.
For example, when using two 120Ω terminators with a
differential driver output voltage of 2V, the DC current is
33mA, which is sourced by the positive voltage supply.
This is true whether the terminators are external or internal
such as in the LTC2854/LTC2855. Power supply current
increases with toggling rate due to capacitive loading and
this term can increase significantly at high data rates. Figure 13 shows supply current vs data rate for two different
capacitive loads for the circuit configuration of Figure 4.
80
SUPPLY CURRENT (mA)
70
CL = 1000pF
50
40
CL = 100pF
30
20
0.1
The logic inputs of the LTC2854/LTC2855 have 150mV of
hysteresis to provide noise immunity. Fast edges on the
outputs can cause glitches in the ground and power supplies
which are exacerbated by capacitive loading. If a logic input
is held near its threshold (typically 1.5V), a noise glitch
from a driver transition may exceed the hysteresis levels
on the logic and data input pins causing an unintended
state change. This can be avoided by maintaining normal
logic levels on the pins and by slewing inputs through
their thresholds by faster than 1V/µs when transitioning.
Good supply decoupling and proper line termination also
reduces glitches caused by driver transitions.
Cable Length vs Data Rate
RDIFF = 54Ω
60
duplex LTC2855, DI and A/B should not be routed near
the driver or receiver outputs.
1
10
DATA RATE (Mbps)
100
285455 F13
Figure 13. Supply Current vs Data Rate
For a given data rate, the maximum transmission distance
is bounded by the cable properties. A typical curve of
cable length vs data rate compliant with the RS485/RS422
standards is shown in Figure 14. Three regions of this
curve reflect different performance limiting factors in data
transmission. In the flat region of the curve, maximum
distance is determined by resistive losses in the cable. The
downward sloping region represents limits in distance and
data rate due to AC losses in the cable. The solid vertical
line represents the specified maximum data rate in the
RS485/RS422 standards. The dashed lines at 20Mbps
show the maximum data rates of the LTC2854/LTC2855.
High Speed Considerations
A ground plane layout is recommended for the LTC2854/
LTC2855. A 0.1µF bypass capacitor less than one-quarter
inch away from the VCC pin is also recommended. The PC
board traces connected to signals A/B and Z/Y (LTC2855)
should be symmetrical and as short as possible to maintain
good differential signal integrity. To minimize capacitive
effects, the differential signals should be separated by
more than the width of a trace and should not be routed
on top of each other if they are on different signal planes.
Care should be taken to route outputs away from any sensitive inputs to reduce feedback effects that might cause
noise, jitter, or even oscillations. For example, in the full
12
CABLE LENGTH (FT)
10k
1k
LTC2854/LTC2855
MAX DATA RATE
100
RS485/RS422
MAX DATA RATE
10
10k
100k
1M
10M
DATA RATE (bps)
100M
285455 F14
Figure 14. Cable Length vs Data Rate (RS485/
RS422 Standards Shown in Vertical Solid Line)
285455fc
For more information www.linear.com/LTC2854
LTC2854/LTC2855
TYPICAL APPLICATION
Failsafe “0” Application (Idle State = Logic “0”)
VCC
100kΩ
RO
LTC2854
R
I1
B
A
DI
I2
D
"A"
"B"
285455 TA03
285455fc
For more information www.linear.com/LTC2854
13
LTC2854/LTC2855
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699 Rev C)
0.70 ±0.05
3.55 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
PACKAGE
OUTLINE
0.25 ±0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ±0.10
(4 SIDES)
R = 0.125
TYP
6
0.40 ±0.10
10
1.65 ±0.10
(2 SIDES)
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
5
0.75 ±0.05
0.00 – 0.05
1
(DD) DFN REV C 0310
0.25 ±0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
14
285455fc
For more information www.linear.com/LTC2854
LTC2854/LTC2855
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DE/UE Package
12-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1695 Rev D)
0.70 ±0.05
3.30 ±0.05
3.60 ±0.05
2.20 ±0.05
1.70 ±0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
2.50 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10
(2 SIDES)
7
R = 0.115
TYP
0.40 ±0.10
12
R = 0.05
TYP
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
3.30 ±0.10
3.00 ±0.10
(2 SIDES)
1.70 ±0.10
0.75 ±0.05
6
0.25 ±0.05
1
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
(UE12/DE12) DFN 0806 REV D
0.50 BSC
2.50 REF
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE A VARIATION OF VERSION
(WGED) IN JEDEC PACKAGE OUTLINE M0-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
285455fc
For more information www.linear.com/LTC2854
15
LTC2854/LTC2855
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641 Rev B)
.189 – .196*
(4.801 – 4.978)
.045 ±.005
16 15 14 13 12 11 10 9
.254 MIN
.009
(0.229)
REF
.150 – .165
.229 – .244
(5.817 – 6.198)
.0165 ±.0015
.150 – .157**
(3.810 – 3.988)
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1
.015 ±.004
× 45°
(0.38 ±0.10)
.007 – .0098
(0.178 – 0.249)
.0532 – .0688
(1.35 – 1.75)
2 3
4
5 6
7
8
.004 – .0098
(0.102 – 0.249)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
.008 – .012
(0.203 – 0.305)
TYP
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
.0250
(0.635)
BSC
GN16 REV B 0212
3. DRAWING NOT TO SCALE
4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
16
285455fc
For more information www.linear.com/LTC2854
LTC2854/LTC2855
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMBER
C
06/15
Added H-grade
1-18
Updated DD Package description
14
285455fc
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
For more
information
www.linear.com/LTC2854
17
LTC2854/LTC2855
TYPICAL APPLICATION
Multi-Node Network with End Termination Using the LTC2854
TE = 0V
TE = 0V
D
R
D
R
LTC2854
LTC2854
LTC2854
LTC2854
R
R
TE = 3.3V
TE = 3.3V
D
D
285455 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC485
Low Power RS485 Interface Transceiver
ICC = 300µA (Typ)
LTC491
Differential Driver and Receiver Pair
ICC = 300µA
LTC1480
3.3V Ultralow Power RS485 Transceiver
3.3V Operation
LTC1483
Ultralow Power RS485 Low EMI Transceiver
Controlled Driver Slew Rate
LTC1485
Differential Bus Transceiver
10Mbps Operation
LTC1487
Ultralow Power RS485 with Low EMI, Shutdown and High
Input Impedance
Up to 256 Transceivers on the Bus
LTC1520
50Mbps Precision Quad Line Receiver
Channel-to-Channel Skew 400ps (Typ)
LTC1535
Isolated RS485 Full-Duplex Transceiver
2500VRMS Isolation in Surface Mount Package
LTC1685
52Mbps RS485 Transceiver with Precision Delay
Propagation Delay Skew 500ps (Typ)
LT1785
60V Fault Protected RS485 Transceiver
60V Tolerant, 15kV ESD
LTC2856/LTC2857/ 20Mbps and Slew Rate-Limited, 15kV RS485/RS422
LTC2858
Transceiver
Up to 256 Transceivers on the Bus
LTC2859/LTC2861
5V Integrated, Switchable, 120Ω Termination Resistor, 15kV ESD
20Mbps RS485 Transceiver with Integrated Switchable
Termination
18 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC2854
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC2854
285455fc
LT 0615 REV C • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2015
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