LTC2855HDE#TR [Linear]
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| 型号： | LTC2855HDE#TR |
| 厂家： | 
Linear |
| 描述： | 暂无描述 |
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LTC2854/LTC2855
3.3V 20Mbps RS485/RS422
Transceivers with Integrated
Switchable Termination
FEATURES
DESCRIPTION
The LTC®2854 and LTC2855 are low power, 20Mbps
RS485/RS422 transceivers operating on 3.3V supplies.
Thereceiverincludesalogic-selectable120Ωtermination,
one-eighth unit load supporting up to 256 nodes per bus
(C-, I-Grade), and a failsafe feature that guarantees a high
outputstateunderconditionsoffloatingorshortedinputs.
n
Integrated, Logic-Selectable 120Ω Termination Resistor
n
3.3V Supply Voltage
n
20Mbps Maximum Data Rate
No Damage or Latchup Up to 2ꢀ5V ꢁHM
n
n
ꢁigh Input Impedance Supports 2ꢀ6 Nodes (C-, I-Grade)
n
Operation Up to 12ꢀ°C (ꢁ-Grade)
n
Guaranteed Failsafe Receiver Operation Over the
The driver maintains a high output impedance over the
entire common mode range when disabled or when the
supplyisremoved.Excessivepowerdissipationcausedby
bus contention or a fault is prevented by current limiting
all outputs and by a thermal shutdown.
Entire Common Mode Range
n
Current Limited Drivers and Thermal Shutdown
n
Delayed Micropower Shutdown: 5µA Maximum (C-, I-Grade)
n
Power Up/Down Glitch-Free Driver Outputs
n
Low Operating Current: 370µA Typical in Receive Mode
n
n
EnhancedESDprotectionallowstheLTC2854towithstand
25kV(humanbodymodel)andtheLTC2855towithstand
15kV on the transceiver interface pins without latchup
or damage.
Compatible with TIA/EIA-485-A Specifications
Available in 10-Pin 3mm × 3mm DFN, 12-Pin
4mm × 3mm DFN and 16-Pin SSOP Packages
APPLICATIONS
n
Low Power RS485/RS422 Transceiver
PRODUCT SELECTION GUIDE
n
Level Translator
PART NUMHER
DUPLEX
PACKAGE
n
Backplane Transceiver
LTC2854
HALF
DFN-10
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.
LTC2855
FULL
SSOP-16, DFN-12
TYPICAL APPLICATION
LTC28ꢀ4 at 20Mbps into ꢀ4
Ω
LTC2854
LTC2854
RO
RE
TE
R
R
RO
RE
TE
120Ω
DE
DE
120Ω
D
D
DI
DI
2V/DIV
285455 TA01
LTC2854
120Ω
285455 TA01b
R
20ns/DIV
D
RO RE TE DE DI
285455fc
1
For more information www.linear.com/LTC2854
LTC2854/LTC2855
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (V ) ................................... –0.3V to 7V
Operating Temperature (Note 4)
CC
Logic Input Voltages (RE, DE, DI, TE)............ –0.3V to 7V
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)
Interface I/O:
A, B, Y, Z.......................................(V –15V) to +15V
CC
(A-B) or (B-A) with Terminator Enabled ..................6V
Receiver Output Voltage (RO) ........–0.3V to (V +0.3V)
CC
GN Package ......................................................300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
TOP VIEW
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
RO
RE
V
A
B
Z
CC
RO
RE
1
2
3
4
5
6
12
11
10
9
V
A
B
Z
Y
CC
RO
RE
DE
DI
1
2
3
4
5
10
9
V
B
A
CC
DE
DE
13
11
DI
8
DI
TE
7
NC
Y
TE
8
TE
6
GND
GND
NC
NC
NC
NC
NC
GND
7
NC
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
DE PACKAGE
12-LEAD (4mm × 3mm) PLASTIC DFN
EXPOSED PAD (PIN 11) PCB GND CONNECTION
GN PACKAGE
16-LEAD (NARROW 0.150) PLASTIC SSOP
T
= 150°C, θ = 43°C/W
EXPOSED PAD (PIN 13) PCB GND CONNECTION
JMAX
JA
θ
= 2.96°C/W
T
JMAX
= 150°C, θ = 44°C/W
JC
JA
T
= 150°C, θ = 110°C/W
JMAX
JA
θ
= 4.3°C/W
JC
θ
= 40°C/W
JC
ORDER INFORMATION
LEAD FREE FINISꢁ
LTC2854CDD#PBF
LTC2854IDD#PBF
LTC2854HDD#PBF
LTC2855CDE#PBF
LTC2855IDE#PBF
LTC2855HDE#PBF
LTC2855CGN#PBF
LTC2855IGN#PBF
LTC2855HGN#PBF
LEAD HASED FINISꢁ
LTC2854CDD
TAPE AND REEL
PART MARKING*
LCQG
LCQG
LCQG
2855
2855
2855
2855
2855I
2855H
PART MARKING*
LCQG
LCQG
LCQG
2855
2855
2855
2855
PACKAGE DESCRIPTION
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
0°C to 70°C
–40°C to 85°C
–40°C to 125°C
0°C to 70°C
LTC2854CDD#TRPBF
LTC2854IDD#TRPBF
LTC2854HDD#TRPBF
LTC2855CDE#TRPBF
LTC2855IDE#TRPBF
LTC2855HDE#TRPBF
LTC2855CGN#TRPBF
LTC2855IGN#TRPBF
LTC2855HGN#TRPBF
TAPE AND REEL
10-Lead (3mm × 3mm) Plastic DFN
10-Lead (3mm × 3mm) Plastic DFN
10-Lead (3mm × 3mm) Plastic DFN
12-Lead (4mm × 3mm) Plastic DFN
12-Lead (4mm × 3mm) Plastic DFN
12-Lead (4mm × 3mm) Plastic DFN
16-Lead (Narrow 0.150) Plastic SSOP
16-Lead (Narrow 0.150) Plastic SSOP
16-Lead (Narrow 0.150) Plastic SSOP
PACKAGE DESCRIPTION
10-Lead (3mm × 3mm) Plastic DFN
10-Lead (3mm × 3mm) Plastic DFN
10-Lead (3mm × 3mm) Plastic DFN
12-Lead (4mm × 3mm) Plastic DFN
12-Lead (4mm × 3mm) Plastic DFN
12-Lead (4mm × 3mm) Plastic DFN
16-Lead (Narrow 0.150) Plastic SSOP
16-Lead (Narrow 0.150) Plastic SSOP
16-Lead (Narrow 0.150) Plastic SSOP
LTC2854CDD#TR
LTC2854IDD#TR
LTC2854IDD
LTC2854HDD
LTC2855CDE
LTC2855IDE
LTC2854HDD#TR
LTC2855CDE#TR
LTC2855IDE#TR
LTC2855HDE
LTC2855CGN
LTC2855IGN
LTC2855HDE#TR
LTC2855CGN#TR
LTC2855IGN#TR
2855I
2855H
–40°C to 85°C
–40°C to 125°C
LTC2855HGN
LTC2855HGN#TR
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/
285455fc
2
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 = 2ꢀ°C, VCC = 3.3V unless otherwise noted (Note 2).
SYMHOL
Driver
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
l
l
|V
OD
|
Differential Driver Output Voltage
R = ∞, V = 3V (Figure 1)
V
V
V
V
V
V
CC
CC
CC
CC
R = 27Ω, V = 3V (Figure 1)
1.5
2
CC
R = 50Ω, V = 3.13V (Figure 1)
CC
l
D|V
|
OD
Change in Magnitude of Driver
Differential Output Voltage for
Complementary Output States
R = 27Ω or R = 50Ω (Figure 1)
0.2
V
l
l
V
Driver Common Mode Output Voltage
R = 27Ω or R = 50Ω (Figure 1)
R = 27Ω or R = 50Ω (Figure 1)
3
V
V
OC
D|V
|
Change in Magnitude of Driver
Common Mode Output Voltage for
Complementary Output States
0.2
OC
l
l
I
I
Driver Three-State (High Impedance)
Output Current on Y and Z
DE = OV, (Y or Z) = –7V, 12V (LTC2855)
H-Grade
10
50
µA
µA
OZD
Maximum Driver Short-Circuit Current
–7V ≤ (Y or Z) ≤ 12V (Figure 2)
180
250
300
mA
mA
OSD
l
–250
–100
Receiver
l
l
I
IN
Receiver Input Current (A, B)
DE = TE = 0V, V = 0V or 3.3V, V = 12V
125
250
µA
µA
CC
IN
(Figure 3) (C-, I-Grade)
DE = TE = 0V, V = 0V or 3.3V, V = –7V,
CC
IN
(Figure 3) (C-, I-Grade)
l
l
DE = TE = 0V, V = 0V or 3.3V, V = 12V
µA
µA
CC
IN
(Figure 3) (H-Grade)
DE = TE = 0V, V = 0V or 3.3V, V = –7V,
–145
96
CC
IN
(Figure 3) (H-Grade)
l
l
l
R
Receiver Input Resistance
RE = V or 0V, DE = TE = 0V,
125
125
kΩ
kΩ
V
IN
CC
V
= –7V, –3V, 3V, 7V, 12V (Figure 3)
IN
(C-, I-Grade)
RE = V or 0V, DE = TE = 0V,
48
CC
V
= –7V, –3V, 3V, 7V, 12V (Figure 3)
IN
(H-Grade)
V
Receiver Differential Input Threshold
Voltage
–7V ≤ B ≤ 12V
0.2
TH
DV
Receiver Input Hysteresis
B = 0V
25
mV
V
TH
l
l
l
V
V
Receiver Output HIGH Voltage
Receiver Output LOW Voltage
I(RO) = –4mA, A-B = 200mV, V = 3V
2.4
OH
CC
I(RO) = 4mA, A-B = –200mV, V = 3V
0.4
1
V
OL
CC
I
Receiver Three-State (High Impedance) RE = V , 0V ≤ RO ≤ V
Output Current on RO
µA
OZR
CC
CC
l
l
I
Receiver Short-Circuit Current
0V ≤ RO ≤ V
85
mA
Ω
OSR
CC
R
Receiver Input Terminating Resistor
TE = V , V = 2V, V = –7V, 0V, 10V
108
2
120
156
TERM
CC AB
B
(Figure 8)
Logic
l
l
l
V
V
Logic Input High Voltage
Logic Input Low Voltage
Logic Input Current
V
V
= 3.6V
V
V
IH
IL
CC
= 3V
0.8
10
CC
I
INL
0
µA
Supplies
I
Supply Current in Shutdown Mode
Supply Current in Receive Mode
DE = 0V, RE = V , TE = 0V
CCS
CCR
CC
l
l
(C-, I-Grade)
(H-Grade)
0
0
5
µA
µA
15
l
I
DE = 0V, RE = 0V, TE = 0V
370
900
µA
285455fc
3
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 = 2ꢀ°C, VCC = 3.3V, TE = 0V unless otherwise noted (Note 2).
SYMHOL
PARAMETER
CONDITIONS
No Load, DE = V , RE = V , TE = 0V
MIN
TYP
450
450
MAX
1000
1000
UNITS
µA
l
l
I
I
Supply Current in Transmit Mode
CCT
CC
CC
Supply Current with Both Driver and
Receiver Enabled
No Load, DE = V , RE = 0V, TE = 0V
µA
CCTR
CC
l
l
I
I
Supply Current in Termination Mode
DE = 0V, RE = V , TE = V
CC
110
450
180
950
µA
µA
CCTERM
CC
Supply Current in Receive and
Termination Mode
DE = 0V, RE = 0V, TE = V
CC
CCTERMR
l
l
I
I
Supply Current in Transmit and
Termination Mode
DE = V , RE = V , TE = V
CC
470
470
1000
1000
µA
µA
CCTERMT
CC
CC
Supply Current with Driver, Receiver
and Termination Enabled
DE = V , RE = 0V, TE = V
CC CC
CCTERMTR
ESD Protection
ESD Protection for RS485/RS422 Pins
A, B on LTC2854, Human Body Model
Y, Z, A, B on LTC2855, Human Body Model
25
15
kV
kV
SWITCHING CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 2ꢀ°C, VCC = 3.3V, TE = 0V unless otherwise noted (Note 2).
SYMHOL
Driver
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
l
l
f
t
Maximum Data Rate
Note 3
20
Mbps
ns
MAX
, t
Driver Input to Output
R
DIFF
R
DIFF
= 54Ω, C = 100pF (Figure 4)
10
1
50
6
PLHD PHLD
L
Dt
Driver Input to Output Difference
= 54Ω, C = 100pF (Figure 4)
ns
PD
L
|t
-t
|
PLHD PHLD
l
l
l
l
l
t
t
t
t
t
Driver Output Y to Output Z
Driver Rise or Fall Time
Driver Enable or Disable Time
Driver Enable from Shutdown
Time to Shutdown
R
R
= 54Ω, C = 100pF (Figure 4)
1
4
6
12.5
70
ns
ns
ns
µs
ns
SKEWD
DIFF
DIFF
L
, t
RD FD
= 54Ω, C = 100pF (Figure 4)
L
, t , t , t
ZLD ZHD LZD HZD
R = 500Ω, C = 50pF, RE = 0 (Figure 5)
L L
, t
R = 500Ω, C = 50pF, RE = V (Figure 5)
8
ZHSD ZLSD
L
L
CC
R = 500Ω, C = 50pF
100
SHDN
L
L
(DE = ↓, RE = V ) or (DE = 0, RE ↑)
CC
(Figure 5)
Receiver
l
l
t
, t
Receiver Input to Output
Differential Receiver Skew
C = 15pF, V = 1.5V, |V | = 1.5V, t and
F
50
1
70
6
ns
ns
PLHR PHLR
L
CM
AB
R
t < 4ns (Figure 6)
t
C = 15pF (Figure 6)
L
SKEWR
|t
-t
|
PLHR PHLR
l
l
l
l
t
t
t
t
, t
Receiver Output Rise or Fall Time
Receiver Enable/Disable
C = 15pF (Figure 6)
3
12.5
50
ns
ns
µs
µs
RR FR
L
, t , t , t
ZLR ZHR LZR HZR
R = 1k, C =15pF, DE = V (Figure 7)
L L CC
, t
Receiver Enable from Shutdown
Termination Enable or Disable Time
R = 1k, C = 15pF, DE = 0V (Figure 7)
8
ZHSR ZLSR
L
L
, t
V = 0V, V = 2V, RE = V , DE = 0V
100
RTEN RTZ
B
AB
CC
(Figure 8)
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.
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
4
For more information www.linear.com/LTC2854
LTC2854/LTC2855
TEST CIRCUITS
Y
Z
Y
R
R
I
GND
OR
CC
OSD
GND
+
OD
–
OR
DI
V
DI
DRIVER
DRIVER
V
V
CC
Z
+
+
–7V to +12V
V
OC
–
–
285455 F01-2
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
I
IN
A OR B
B OR A
RECEIVER
+
V
IN
–
285455 F03
V
I
IN
IN
R
IN
=
Figure 3. Receiver Input Current and Input Resistance
V
CC
t
t
PHLD
DI
Y, Z
Y-Z
PLHD
Y
Z
0V
C
C
t
L
L
SKEWD
DI
DRIVER
R
DIFF
V
1/2 V
O
O
285455 F04a
90%
90%
10%
0
0
10%
285455 F04b
t
t
FD
RD
Figure 4. Driver Timing Measurement
V
CC
DE
Y OR Z
Z OR Y
1/2 V
CC
GND
OR
CC
R
R
L
Y
0V
t
t
,
ZLD
t
V
LZD
ZLSD
C
L
L
V
CC
OL
V
OR
GND
CC
DI
V
O
1/2 V
1/2 V
DRIVER
DE
CC
0.5V
0.5V
V
V
V
CC
L
OR
GND
OH
0V
Z
CC
C
285455 F05b
t
,
t
,
HZD
ZHD
285455 F05a
t
t
SHDN
ZHSD
Figure ꢀ. Driver Enable and Disable Timing Measurements
285455fc
5
For more information www.linear.com/LTC2854
LTC2854/LTC2855
TEST CIRCUITS
t
t
R
F
V
AB
AB
90%
0
90%
10%
A
A-B
V
/2
/2
AB
10%
–V
RO
t
t
PHLR
V
RECEIVER
PLHR
CM
V
B
C
V
L
CC
0
90%
10%
90%
AB
1/2 V
1/2 V
CC
RO
V
O
CC
285455 F06a
10%
t
t
RR
FR
t
= t
– t
SKEWR
PLHR PHLR
285455 F06b
Figure 6. Receiver Propagation Delay Measurements
V
CC
RE
RO
RO
1/2 V
CC
0V
t
,
ZLR
A
B
t
t
t
LZR
ZLSR
0V OR V
CC
V
R
V
OR
GND
CC
OL
L
CC
RO
V
O
1/2 V
RECEIVER
RE
CC
0.5V
0.5V
V
C
V
OR 0V
L
CC
V
OH
1/2 V
CC
0V
285455 F07b
DI = 0V OR V
285455 F07a
CC
t
,
ZHR
HZR
t
ZHSR
Figure 7. Receiver Enable and Disable Timing Measurements
V
AB
R
=
TERM
I
A
I
V
A
CC
A
B
TE
1/2 V
CC
RO
+
–
RECEIVER
V
V
0V
AB
t
RTEN
t
RTZ
90%
I
A
TE
10%
+
–
B
285455 F08
Figure 8. Termination Resistance and Timing Measurements
285455fc
6
For more information www.linear.com/LTC2854
LTC2854/LTC2855
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 2ꢀ°C, VCC = 3.3V, unless otherwise noted.
Receiver S5ew
Driver Propagation Delay
vs Temperature
Driver S5ew vs Temperature
vs Temperature
2
18
V
C
= 1.5V
R
C
= 54Ω
DIFF
R
C
= 54Ω
AB
L
DIFF
= 15pF
= 100pF
L
= 100pF
L
16
14
1
0
1
12
10
9
0
–1
6
–1
4
0
20 40 60
120
–40 –20
0
20 40 60 80 100 120
TEMPERATURE (˚C)
285455 G02
–40 –20
80 100
0
20 40 60
120
80 100
–40 –20
TEMPERATURE (˚C)
TEMPERATURE (˚C)
285455 G01
285455 G03
Driver Output Low/ꢁigh Voltage
vs Output Current
Driver Differential Output Voltage
vs Temperature
RTERM vs Temperature
135
130
R
DIFF
=
∞
3
3
V
OH
R
R
= 100Ω
= 54Ω
DIFF
125
120
115
110
105
2
1
2
1
DIFF
V
OL
100
0
0
0
20 40 60
120
80 100
–40 –20
20
30
40
50
70
0
10
60
0
20 40 60
TEMPERATURE (˚C)
120
80 100
–40 –20
TEMPERATURE (˚C)
OUTPUT CURRENT (mA)
285455 G04
285455 G05
285455 G06
Receiver Output Voltage vs
Receiver Propagation Delay
vs Temperature
Output Current (Source and Sin5)
Supply Current vs Data Rate
70
65
60
50
40
30
20
10
0
V
C
= 1.5V
C
= 100pF
AB
L
L
SOURCE
= 15pF
3
60
R
R
= 54Ω
DIFF
55
50
45
40
2
1
= 100Ω
DIFF
SINK
R
DIFF
=
∞
35
0
0
20 40 60
120
80 100
2
3
4
5
6
–40 –20
0
1
0.1
1
10
100
TEMPERATURE (˚C)
DATA RATE (Mbps)
OUTPUT CURRENT (mA)
285455 G08
285455 G07
285455 G09
285455fc
7
For more information www.linear.com/LTC2854
LTC2854/LTC2855
PIN FUNCTIONS
(DD/DE/GN)
RO (Pin 1): Receiver Output. If the receiver output is en-
abled (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.
TE (Pin ꢀ): 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.
RE (Pin 2): Receiver Enable. A low enables the receiver.
A high input forces the receiver output into a high imped-
ance state.
Y (Pins NA/8/12): Positive Driver Output for LTC2855.
Z (Pins NA/9/13): Negative Driver Output for LTC2855.
DE (Pin 3): Driver Enable. A high on DE enables the driver.
A low input will force the driver outputs into a high imped-
ance. If RE is high with DE and TE low, the part will enter
a low power shutdown state.
H (Pins 9/10/14): Negative Receiver Input (and Negative
Driver Output for LTC2854).
A (Pins 8/11/1ꢀ): Positive Receiver Input (and Positive
Driver Output for LTC2854).
DI (Pin 4): Driver Input. If the driver outputs are enabled
(DE high), then a low on DI forces the driver positive out-
put low and negative output high. A high on DI, with the
driver outputs enabled, forces the driver positive output
high and negative output low.
V
(Pins 10/12/16): Positive Supply. V = 3.0V < V
<
CC
CC
CC
3.6V. Bypass with 0.1µF ceramic capacitor.
285455fc
8
For more information www.linear.com/LTC2854
LTC2854/LTC2855
FUNCTION TABLES
LTC28ꢀ4
LOGIC INPUTS
DE
0
RE
0
TE
0
MODE
RECEIVE
A, H
RO
TERMINATOR
R
IN
DRIVEN
DRIVEN
HIGH-Z
HIGH-Z
DRIVEN
DRIVEN
OFF
ON
0
0
1
RECEIVE WITH TERM
SHUTDOWN
R
R
TERM
0
1
0
R
IN
OFF
ON
0
1
1
TERM ONLY
TERM
1
0
0
TRANSMIT WITH RECEIVE
DRIVEN
DRIVEN
OFF
ON
1
0
1
TRANSMIT WITH RECEIVE
AND TERM
1
1
1
1
0
1
TRANSMIT
DRIVEN
DRIVEN
HIGH-Z
HIGH-Z
OFF
ON
TRANSMIT WITH TERM
LTC28ꢀꢀ
LOGIC INPUTS
DE
0
RE
0
TE
0
MODE
RECEIVE
A, H
Y, Z
RO
TERMINATOR
R
IN
HIGH-Z
HIGH-Z
HIGH-Z
HIGH-Z
DRIVEN
DRIVEN
DRIVEN
DRIVEN
HIGH-Z
HIGH-Z
DRIVEN
DRIVEN
OFF
ON
0
0
1
RECEIVE WITH TERM
SHUTDOWN
R
R
R
TERM
0
1
0
R
IN
OFF
ON
0
1
1
TERM ONLY
TERM
1
0
0
TRANSMIT WITH RECEIVE
R
IN
OFF
ON
1
0
1
TRANSMIT WITH RECEIVE
AND TERM
TERM
1
1
1
1
0
1
TRANSMIT
R
DRIVEN
DRIVEN
HIGH-Z
HIGH-Z
OFF
ON
IN
TRANSMIT WITH TERM
R
TERM
BLOCK DIAGRAMS
LTC28ꢀ4
LTC28ꢀꢀ
V
V
CC
CC
A
25kV
A
(15kV)
RE
RE
SLEEP/SHUTDOWN
LOGIC AND DELAY
SLEEP/SHUTDOWN
LOGIC AND DELAY
120Ω
TERM
120Ω
TERM
DE
R
DE
R
TE
TE
125k
IN
125k
IN
R
R
RO
RO
RECEIVER
RECEIVER
B
25kV
B
(15kV)
125k
125k
IN
R
R
IN
Z
(15kV)
DI
DI
DRIVER
DRIVER
Y
(15kV)
GND
GND
285455 BD
285455fc
9
For more information www.linear.com/LTC2854
LTC2854/LTC2855
APPLICATIONS INFORMATION
Driver
the inputs are either shorted, left open, or terminated
(externally or internally), but not driven. This failsafe fea-
ture is guaranteed to work for inputs spanning the entire
common mode range of –7V to +12V.
ThedriverprovidesfullRS485/RS422compatibility.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).
The receiver output is internally driven high (to V ) or
CC
low(toground)withnoexternalpull-upneeded. Whenthe
receiver is disabled the RO pin becomes High-Z with leak-
age of less than 1µA for voltages within the supply range.
When the driver is disabled, both outputs are high-
impedance. 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
Receiver Input Resistance
ThereceiverinputresistancefromAorBtogroundisguar-
anteedtobegreaterthan96k(C-,I-Grade)whenthetermi-
nation is disabled. This is 8X higher than the requirements
fortheRS485standardandthusthisreceiverrepresentsa
one-eighth unit load. This, in turn, means that 8X the
standard number of receivers, or 256 total, can be con-
nected 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.
the receiver input resistance, R .
IN
Driver Overvoltage and Overcurrent Protection
The driver outputs are protected from short-circuits to
any voltage within the Absolute Maximum range of (V
CC
–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
V , a reverse current will flow into the supply. When this
CC
voltage exceeds V by about 1.4V, the reverse current
CC
turnsoff.Preventingthedriverfromturningoffwithoutputs
shorted to output voltages just above V keeps the driver
CC
activeevenforreceiverloadsthathaveapositivecommon
mode with respect to the driver—a valid condition.
Theworst-casepeakreverseshort-circuitcurrentcanbeas
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.
>96kΩ
A
60Ω
All devices also feature thermal shutdown protection that
disablesthedriverandreceiverincaseofexcessivepower
dissipation (see Note 4).
TE
60Ω
>96kΩ
B
Receiver and Failsafe
285455 F09
With the receiver enabled, when the absolute value of the
differentialvoltagebetweentheAandBpinsisgreaterthan
200mV, the state of RO will reflect the polarity of (A-B).
Figure 9. Equivalent Input Resistance into A and H
(on the LTC28ꢀ4, Valid if Driver is Disabled)
The LTC2854/LTC2855 have a failsafe feature that guar-
antees the receiver output to be in a logic-high state when
285455fc
10
For more information www.linear.com/LTC2854
LTC2854/LTC2855
APPLICATIONS INFORMATION
Switchable Termination
When the TE pin is high, the termination resistor is en-
abled 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 com-
mon mode range of –7V to +12V as shown in Figure 11.
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,thelineterminationforoptimalperformancewhen
configuring transceiver networks.
The integrated termination resistor has a high frequency
response which does not limit performance at the maxi-
mum specified data rate. Figure 12 shows the magnitude
and phase of the termination impedance vs frequency.
150
V
= 2V
AB
140
130
120
110
100
–10
–5
0
5
10
15
COMMON MODE VOLTAGE (V)
Figure 10. Curve Trace Hetween A and H
with Termination Enabled and Disabled
285455 F11
Figure 11. Typical Resistance of the Enabled
Terminator vs Voltage on H Pin
185
170
155
140
30
15
PHASE
0
–15
–30
–45
–60
MAGNITUDE
125
110
95
80
10
–75
1
–1
0
10
FREQUENCY (MHz)
10
285455 F12
Figure 12. Termination Magnitude
and Phase vs Frequency
285455fc
11
For more information www.linear.com/LTC2854
LTC2854/LTC2855
APPLICATIONS INFORMATION
Supply Current
duplex LTC2855, DI and A/B should not be routed near
the driver or receiver outputs.
The unloaded static supply currents in the LTC2854/
LTC2855areverylow—typicallyunder500µAforallmodes
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.
Thisistruewhethertheterminatorsareexternalorinternal
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. Fig-
ure 13 shows supply current vs data rate for two different
capacitive loads for the circuit configuration of Figure 4.
The logic inputs of the LTC2854/LTC2855 have 150mV of
hysteresis to provide noise immunity. Fast edges on the
outputscancauseglitchesinthegroundandpowersupplies
whichareexacerbatedbycapacitiveloading.Ifalogicinput
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.
80
Cable Length vs Data Rate
R
DIFF
= 54Ω
70
60
50
40
30
20
For a given data rate, the maximum transmission distance
is bounded by the cable properties. A typical curve of
cablelengthvsdataratecompliantwiththeRS485/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
distanceisdeterminedbyresistivelossesinthecable. The
downwardslopingregionrepresentslimitsindistanceand
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.
C
= 1000pF
L
C
= 100pF
L
0.1
1
10
100
DATA RATE (Mbps)
285455 F13
Figure 13. Supply Current vs Data Rate
10k
ꢁigh Speed Considerations
A ground plane layout is recommended for the LTC2854/
LTC2855. A 0.1µF bypass capacitor less than one-quarter
1k
inch away from the V pin is also recommended. The PC
CC
board traces connected to signals A/B and Z/Y (LTC2855)
shouldbesymmetricalandasshortaspossibletomaintain
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.
LTC2854/LTC2855
MAX DATA RATE
100
RS485/RS422
MAX DATA RATE
10
10k
100k
1M
10M
100M
DATA RATE (bps)
285455 F14
Care should be taken to route outputs away from any sen-
sitive inputs to reduce feedback effects that might cause
noise, jitter, or even oscillations. For example, in the full
Figure 14. Cable Length vs Data Rate (RS48ꢀ/
RS422 Standards Shown in Vertical Solid Line)
285455fc
12
For more information www.linear.com/LTC2854
LTC2854/LTC2855
TYPICAL APPLICATION
Failsafe “0” Application (Idle State = Logic “0”)
V
CC
100kΩ
LTC2854
R
RO
DI
I1
B
A
"A"
"B"
D
I2
285455 TA03
285455fc
13
For more information www.linear.com/LTC2854
LTC2854/LTC2855
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/pac5aging/ for the most recent pac5age 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
2.15 ±0.05 (2 SIDES)
1.65 ±0.05
PACKAGE
OUTLINE
0.25 ±0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.125
0.40 ±0.10
TYP
6
10
3.00 ±0.10
(4 SIDES)
1.65 ±0.10
(2 SIDES)
PIN 1 NOTCH
R = 0.20 OR
PIN 1
TOP MARK
(SEE NOTE 6)
0.35 × 45°
CHAMFER
(DD) DFN REV C 0310
5
1
0.25 ±0.05
0.50 BSC
0.75 ±0.05
0.200 REF
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
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
285455fc
14
For more information www.linear.com/LTC2854
LTC2854/LTC2855
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/pac5aging/ for the most recent pac5age 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
0.40 ±0.10
4.00 ±0.10
(2 SIDES)
R = 0.115
TYP
7
12
R = 0.05
TYP
3.30 ±0.10
3.00 ±0.10
(2 SIDES)
1.70 ±0.10
PIN 1
TOP MARK
(NOTE 6)
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
(UE12/DE12) DFN 0806 REV D
6
1
0.25 ±0.05
0.75 ±0.05
0.200 REF
0.50 BSC
2.50 REF
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
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
15
For more information www.linear.com/LTC2854
LTC2854/LTC2855
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/pac5aging/ for the most recent pac5age drawings.
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641 Rev B)
.189 – .196*
.045 .005
(4.801 – 4.978)
.009
(0.229)
REF
16 15 14 13 12 11 10 9
.254 MIN
.150 – .165
.229 – .244
.150 – .157**
(5.817 – 6.198)
(3.810 – 3.988)
.0165 .0015
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1
2
3
4
5
6
7
8
.015 .004
(0.38 0.10)
× 45°
.0532 – .0688
(1.35 – 1.75)
.004 – .0098
(0.102 – 0.249)
.007 – .0098
(0.178 – 0.249)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
.0250
(0.635)
BSC
.008 – .012
GN16 REV B 0212
(0.203 – 0.305)
TYP
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
3. DRAWING NOT TO SCALE
4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
285455fc
16
For more information www.linear.com/LTC2854
LTC2854/LTC2855
REVISION HISTORY
REV
DATE
06/15 Added H-grade
Updated DD Package description
DESCRIPTION
PAGE NUMHER
C
1-18
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
17
LTC2854/LTC2855
TYPICAL APPLICATION
Multi-Node Networ5 with End Termination Using the LTC28ꢀ4
TE = 0V
TE = 0V
D
D
R
R
LTC2854
LTC2854
LTC2854
LTC2854
R
R
TE = 3.3V
TE = 3.3V
D
D
285455 TA04
RELATED PARTS
PART NUMHER
LTC485
DESCRIPTION
COMMENTS
Low Power RS485 Interface Transceiver
Differential Driver and Receiver Pair
3.3V Ultralow Power RS485 Transceiver
I
= 300µA (Typ)
CC
CC
LTC491
I
= 300µA
LTC1480
LTC1483
LTC1485
LTC1487
3.3V Operation
Ultralow Power RS485 Low EMI Transceiver
Differential Bus Transceiver
Controlled Driver Slew Rate
10Mbps Operation
Ultralow Power RS485 with Low EMI, Shutdown and High
Input Impedance
Up to 256 Transceivers on the Bus
LTC1520
LTC1535
LTC1685
LT1785
50Mbps Precision Quad Line Receiver
Isolated RS485 Full-Duplex Transceiver
52Mbps RS485 Transceiver with Precision Delay
60V Fault Protected RS485 Transceiver
Channel-to-Channel Skew 400ps (Typ)
2500V
Isolation in Surface Mount Package
RMS
Propagation Delay Skew 500ps (Typ)
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 20Mbps RS485 Transceiver with Integrated Switchable
Termination
5V Integrated, Switchable, 120Ω Termination Resistor, 15kV ESD
285455fc
LT 0615 REV C • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
18
●
●
LINEAR TECHNOLOGY CORPORATION 2015
(408)432-1900 FAX: (408) 434-0507 www.linear.com/LTC2854
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