LINER LTC2851CDD

LTC2850/LTC2851/LTC2852
3.3V 20Mbps RS485/RS422
Transceivers
FEATURES
DESCRIPTION
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The LTC®2850, LTC2851, and LTC2852 are low power,
20Mbps RS485/RS422 transceivers operating on 3.3V
supplies. The receiver has a 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.
n
n
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n
n
n
n
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n
n
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3.3V Supply Voltage
20Mbps Maximum Data Rate
No Damage or Latchup Up to ±15kV HBM
High Input Impedance Supports 256 Nodes
(C, I-Grade)
Operation Up to 125°C (H-Grade)
Guaranteed Failsafe Receiver Operation Over the
Entire Common Mode Range
Current Limited Drivers and Thermal Shutdown
Delayed Micropower Shutdown: 5μA Maximum
(C, I-Grade)
Power Up/Down Glitch-Free Driver Outputs
Low Operating Current: 370μA Typical in Receive
Mode
Compatible with TIA/EIA-485-A Specifications
Available in 8-Pin and 10-Pin 3mm × 3mm DFN,
8-Pin and 10-Pin MSOP, and 8-Pin and 14-Pin SO
Packages
APPLICATIONS
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Low Power RS485/RS422 Transceiver
Level Translator
Backplane Transceiver
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 thermal shutdown.
Enhanced ESD protection allows these parts to withstand
up to ±15kV (human body model) on the transceiver
interface pins without latchup or damage.
PART NUMBER
DUPLEX
PACKAGE
LTC2850
Half
SO-8, MSOP-8, DFN-8
LTC2851
Full
SO-8, MSOP-8, DFN-8
LTC2852
Full
SO-14, MSOP-10, DFN-10
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
LTC2850 at 20Mbps Into 54Ω
LTC2850
RO1
RE1
R
VCC1
DI
RT
DE1
DI1
D
A
GND1
B
2V/DIV
A-B
LTC2850
RO2
RE2
R
VCC2
20ns/DIV
DE2
DI2
RT
D
285012 TA01b
GND2
285012 TA01a
285012fc
1
LTC2850/LTC2851/LTC2852
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (VCC) ................................... –0.3V to 7V
Logic Input Voltages (RE, DE, DI) ................ –0.3V to 7V
Interface I/O:
A, B, Y, Z .......................................(VCC – 15V) to 15V
Receiver Output Voltage (RO) .......–0.3V to (VCC + 0.3V)
Operating Temperature (Note 4)
LTC285xC................................................. 0°C to 70°C
LTC285xI .............................................. –40°C to 85°C
LTC285xH .......................................... –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MSOP ............................................................... 300°C
PIN CONFIGURATION
LTC2850
TOP VIEW
TOP VIEW
RO
1
8
VCC
RE
2
7
B
DE
3
6
A
DI
4
5
GND
9
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
TOP VIEW
RO
RE
DE
DI
8
7
6
5
1
2
3
4
VCC
B
A
GND
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 200°C/W, θJC = 40°C/W
TJMAX = 150°C, θJA = 43°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
RO
1
8
VCC
RE
2
7
B
DE
3
6
A
DI
4
5
GND
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 150°C/W, θJC = 39°C/W
LTC2851
TOP VIEW
TOP VIEW
VCC
1
8
A
RO
2
7
B
DI
3
6
Z
GND
4
5
Y
9
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
TOP VIEW
VCC
RO
DI
GND
1
2
3
4
8
7
6
5
A
B
Z
Y
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 200°C/W, θJC = 40°C/W
TJMAX = 150°C, θJA = 43°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
VCC
1
8
A
RO
2
7
B
DI
3
6
Z
GND
4
5
Y
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 150°C/W, θJC = 39°C/W
TOP VIEW
LTC2852
TOP VIEW
TOP VIEW
RO
10 VCC
1
RE
2
DE
3
DI
4
7 Z
GND
5
6 Y
9 A
11
8 B
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 150°C, θJA = 43°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
RO
RE
DE
DI
GND
1
2
3
4
5
10
9
8
7
6
VCC
A
B
Z
Y
MS PACKAGE
10-LEAD PLASTIC MSOP
NC 1
14 VCC
RO 2
13 NC
RE 3
12 A
DE 4
11 B
DI 5
10 Z
GND 6
9
Y
GND 7
8
NC
TJMAX = 150°C, θJA = 120°C/W, θJC = 45°C/W
S PACKAGE
14-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 88°C/W, θJC = 37°C/W
285012fc
2
LTC2850/LTC2851/LTC2852
ORDER INFORMATION
LTC2850 C
DD
#TR PBF
LEAD FREE DESIGNATOR
PBF = Lead Free
TAPE AND REEL
TR = Tape and Reel
PACKAGE TYPE
DD = 8-Lead Plastic DFN
DD = 10-Lead Plastic DFN
MS8 = 8-Lead Plastic MSOP
MS = 10-Lead Plastic MSOP
S8 = 8-Lead Plastic SO
S = 14-Lead Plastic SO
TEMPERATURE GRADE
C = Commercial Temperature Range (0°C to 70°C)
I = Industrial Temperature Range (–40°C to 85°C)
H = Automotive Temperature Range (–40°C to 125°C)
PRODUCT PART NUMBER
LTC2850 = Half Duplex, with Enables
LTC2851 = Full Duplex, No Enables
LTC2852 = Full Duplex, with Enables
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
PRODUCT SELECTION GUIDE
PART NUMBER
PART MARKING
DUPLEX
LOW POWER SHUTDOWN MODE
PACKAGE
LTC2850
2850/I/H, LTCQD, LCQC
Half
Yes
SO-8, MSOP-8, DFN-8
LTC2851
2851/I/H, LTCWF, LCWD
Full
No
SO-8, MSOP-8, DFN-8
LTC2852
2852CS/IS/HS, LTCRX, LCRY
Full
Yes
SO-14, MSOP-10, DFN-10
285012fc
3
LTC2850/LTC2851/LTC2852
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
Differential Driver Output Voltage
R = ∞, VCC = 3V (Figure 1)
R = 27Ω, VCC = 3V (Figure 1)
R = 50Ω, VCC = 3.13V (Figure 1)
MIN
TYP
MAX
UNITS
VCC
VCC
VCC
V
V
V
Driver
|VOD|
l
l
l
1.5
2
Δ|VOD|
Difference in Magnitude of Driver Differential R = 27Ω or 50Ω (Figure 1)
Output Voltage for Complementary Output
States
l
0.2
V
VOC
Driver Common Mode Output Voltage
R = 27Ω or 50Ω (Figure 1)
l
3
V
Δ|VOC|
Difference in Magnitude of Driver Common
Mode Output Voltage for Complementary
Output States
R = 27Ω or 50Ω (Figure 1)
l
0.2
V
IOZD
Driver Three-State (High Impedance) Output
Current on Y and Z
DE = 0V, (Y or Z) = –7V, 12V (LTC2852)
l
±10
μA
IOSD
Maximum Driver Short-Circuit Current
–7V ≤ (Y or Z) ≤ 12V (Figure 2)
±250
300
mA
mA
125
μA
l
±180
–250
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
–100
μA
250
μA
μA
l
VTH
Receiver Differential Input Threshold Voltage –7V ≤ B ≤ 12V
ΔVTH
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 (LTC2850, LTC2852)
l
±1
μA
IOSR
Receiver Short-Circuit Current
0V ≤ RO ≤ VCC
l
±85
mA
VIH
Logic Input High Voltage
VCC = 3.6V
l
VIL
Logic Input Low Voltage
VCC = 3V
l
IINL
Logic Input Current
±0.2
25
V
mV
2.4
V
Logic
l
2
V
0
0.8
V
±10
μA
285012fc
4
LTC2850/LTC2851/LTC2852
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
TYP
MAX
Supply Current in Shutdown Mode
DE = 0V, RE = VCC,
LTC2850, LTC2852 (C and I-Grade)
LTC2850, LTC2852 (H-Grade)
Supply Current in Receive Mode
ICCT
ICCTR
UNITS
l
0
5
μA
l
0
15
μA
DE = 0V, RE = 0V (LTC2850, LTC2852)
l
370
900
μA
Supply Current in Transmit Mode
No Load, DE = VCC, RE = VCC (LTC2850,
LTC2852)
l
450
1000
μA
Supply Current with Both Driver and
Receiver Enabled
No Load, DE = VCC, RE = 0V
l
450
1000
μA
Supplies
ICCS
ICCR
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, unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
Maximum Data Rate
(Note 3)
l
TYP
MAX
UNITS
Driver
fMAX
20
Mbps
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
10
50
ns
ΔtPD
Driver Input to Output Difference
|tPLHD – tPHLD|
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
1
6
ns
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 = 0V (Figure 5)
(LTC2850, LTC2852)
l
70
ns
tZHSD, tZLSD Driver Enable from Shutdown
RL = 500Ω, CL = 50pF, RE = VCC (Figure 5)
(LTC2850, LTC2852)
l
8
μs
tSHDN
RL = 500Ω, CL = 50pF, (DE = ↓, RE = VCC)
or (DE = 0V, RE = ↑) (Figure 5) (LTC2850,
LTC2852)
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
CL = 15pF (Figure 6)
l
3
12.5
ns
tZLR, tZHR,
tLZR, tHZR
Receiver Enable/Disable
RL =1k, CL =15pF, DE = VCC (Figure 7)
(LTC2850, LTC2852)
l
50
ns
RL = 1k, CL = 15pF, DE = 0V (Figure 7)
(LTC2850, LTC2852)
l
8
μs
tPLHD, tPHLD Driver Input to Output
Time to Shutdown
Receiver
tZHSR, tZLSR Receiver Enable from Shutdown
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.
285012fc
5
LTC2850/LTC2851/LTC2852
TEST CIRCUITS
Y
GND
OR
VCC
DI
Y
+
DRIVER
R
GND
OR
VCC
VOD
–
R
+
–
IOSD
DI
DRIVER
VOC
Z
+
–
Z
285012 F01
–7V TO 12V
285012 F02
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
IIN
VIN
+
–
A OR B
RECEIVER
B OR A
285012 F03
V
RIN = IN
IIN
Figure 3. Receiver Input Current and Input Resistance
VCC
tPLHD
DI
Y
DI
tPHLD
0V
tSKEWD
CL
DRIVER
Y, Z
RDIFF
VO
1/2 VO
CL
Z
285012 F04a
90%
(Y-Z)
10%
90%
0
0
tRD
10%
tFD
285012 F04b
Figure 4. Driver Timing Measurement
285012fc
6
LTC2850/LTC2851/LTC2852
TEST CIRCUITS
VCC
RL
Y
VCC
OR
GND
DI
CL
DE
GND
OR
VCC
1/2 VCC
0V
tZLD,
tZLSD
VCC
DRIVER
VO
Y OR Z
RL
DE
Z
CL
VCC
OR
GND
285012 F05a
tLZD
1/2 VCC
0.5V
VOL
VOH
0.5V
1/2 VCC
Z OR Y
0V
tZHD,
tZHSD
285012 F05b
tHZD,
tSHDN
Figure 5. Driver Enable and Disable Timing Measurements
tR
VAB
A-B
–VAB
A
±VAB/2
VCM
RECEIVER
RO
B
±VAB/2
CL
90%
10%
VO
RO
90%
0
10%
tPLHR
VCC
0
285012 F06a
tF
tPHLR
90%
1/2 VCC
10%
90%
10%
1/2 VCC
tRR
tFR
285012 F06b
tSKEWR = |tPLHR – tPHLR|
Figure 6. Receiver Propagation Delay Measurements
RE
0V OR VCC
1/2 VCC
0V
A
RECEIVER
VCC OR 0V
VCC
B
RE
RL
RO
CL
VCC
OR
GND
tZLR,
tZLSR
VCC
VO
RO
tLZR
1/2 VCC
0.5V
VOL
VOH
285012 F07a
0.5V
1/2 VCC
RO
DI = 0V OR VCC
0V
tZHR,
tZHSR
285012 F07b
tHZR
Figure 7. Receiver Enable/Disable Time Measurements
285012fc
7
LTC2850/LTC2851/LTC2852
TYPICAL PERFORMANCE CHARACTERISTICS
Receiver Skew vs Temperature
2
TA = 25°C. VCC = 3.3V unless otherwise noted.
Driver Propagation Delay vs
Temperature
Driver Skew vs Temperature
1.5
VAB = 1.5V
CL = 15pF
18
RDIFF = 54Ω
CL = 100pF
16
1
0
PROP DELAY (ns)
DRIVER SKEW (ns)
RECEIVER SKEW (ns)
1.0
0.5
0
–0.5
0
20 40 60 80
TEMPERATURE (°C)
0
20 40 60 80
TEMPERATURE (°C)
285012 G01
10
4
–40 –20
100 120
0
20 40 60 80
TEMPERATURE (°C)
285012 G02
Driver Output Short-Circuit
Current vs Temperature
100 120
285012 G03
Driver Output Low/High Voltage
vs Output Current
Driver Differential Output Voltage
vs Temperature
150
3.5
3.5
140
3.0
3.0
RDIFF = ∞
SINK
VOUT = 3.3V
120
110
100
SOURCE
VOUT = 0V
90
80
–40 –20
2.5
2.0
1.5
VOL
1.0
0.5
20 40 60 80
TEMPERATURE (°C)
100 120
0
10
30
40
50
20
OUTPUT CURRENT (mA)
SOURCE
PROP DELAY (ns)
OUTPUT VOLTAGE (V)
60
70
2.0
1.5
1.0
60
65
50
60
55
50
0
3
4
2
OUTPUT CURRENT (mA)
5
6
285012 G07
20 40 60 80
TEMPERATURE (°C)
35
–40 –20
100 120
CL = 100pF
RDIFF = 54Ω
40
30
RDIFF = 100Ω
20
RDIFF = ∞
10
40
SINK
0
Supply Current vs Data Rate
70
45
1
1.0
285012 G06
SUPPLY CURRENT (mA)
3.5
0
1.5
Receiver Propagation Delay vs
Temperature
2.5
RDIFF = 54Ω
285012 G05
Receiver Output Voltage vs
Output Current (Source and Sink)
0.5
2.0
0
–40 –20
0
0
RDIFF = 100Ω
2.5
0.5
285012 G04
3.0
OUTPUT VOLTAGE (V)
VOH
130
OUTPUT VOLTAGE (V)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
12
6
–1.5
–40 –20
100 120
14
8
–1.0
–1
–40 –20
RDIFF = 54Ω
CL = 100pF
0
20 40 60 80
TEMPERATURE (°C)
100 120
285012 G08
0
0.1
10
1
DATA RATE (Mbps)
100
285012 G09
285012fc
8
LTC2850/LTC2851/LTC2852
PIN FUNCTIONS
RO: 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 valid signal, RO
will be high.
Y: Noninverting Driver Output for LTC2851 and LTC2852.
High-impedance when driver disabled or unpowered.
RE: Receiver Enable. A low enables the receiver. A high input
forces the receiver output into a high impedance state.
A: Noninverting Receiver Input (and Noninverting Driver
Output for LTC2850). Impedance is >96kΩ in receive
mode or unpowered.
DE: 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 low, the part will enter a low power
shutdown state.
B: Inverting Receiver Input (and Inverting Driver Output
for LTC2850). Impedance is >96kΩ in receive mode or
unpowered.
DI: 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.
Z: Inverting Driver Output for LTC2851 and LTC2852. Highimpedance when driver disabled or unpowered.
VCC: Positive Supply. 3V < VCC < 3.6V. Bypass with 0.1μF
ceramic capacitor.
Exposed Pad: Ground. The exposed pads on the DFN
packages must be soldered to ground.
GND: Ground.
FUNCTION TABLES
LTC2850
Logic Inputs
Mode
A, B
RO
0
Receive
RIN
Driven
0
1
Shutdown
RIN
High-Z
1
0
Transceive
Driven
Driven
1
1
Transmit
Driven
High-Z
DE
RE
0
LTC2852
Logic Inputs
Mode
A, B
Y, Z
RO
0
Receive
RIN
High-Z
Driven
0
1
Shutdown
RIN
High-Z
High-Z
1
0
Transceive
RIN
Driven
Driven
1
1
Transmit
RIN
Driven
High-Z
DE
RE
0
285012fc
9
LTC2850/LTC2851/LTC2852
BLOCK DIAGRAM
LTC2850
LTC2851
LTC2852
VCC
VCC
VCC
A
(15kV)
RO
RECEIVER
RO
RECEIVER
A
(15kV)
RO
RECEIVER
B
(15kV)
RE
DE
A
(15kV)
SLEEP/SHUTDOWN
LOGIC AND DELAY
B
(15kV)
RE
DE
B
(15kV)
SLEEP/SHUTDOWN
LOGIC AND DELAY
Z
(15kV)
DI
DRIVER
DI
DRIVER
Z
(15kV)
DI
DRIVER
Y
(15kV)
285012 BDa
GND
Y
(15kV)
285012 BDc
285012 BDb
GND
GND
APPLICATIONS INFORMATION
Driver
The driver provides full RS485/RS422 compatibility. When
enabled, if DI is high, Y-Z is positive for the full-duplex
devices (LTC2851, LTC2852) and A-B is positive for the
half-duplex device (LTC2850).
When the driver is disabled, both outputs are high-impedance. For the full-duplex devices, 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 LTC2850, 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
can not be absorbed by the supply, a 3.6V zener diode can
be added in parallel with the supply to sink this current.
All devices also feature thermal shutdown protection that
disables the driver and receiver in case of excessive power
dissipation (see Note 4).
Receiver and Failsafe
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).
These parts have a failsafe feature that guarantees the
receiver output to be in a logic-high state when the inputs
are either shorted, left open, or terminated 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.
285012fc
10
LTC2850/LTC2851/LTC2852
APPLICATIONS INFORMATION
Receiver Input Resistance
High Speed Considerations
The receiver input resistance from A or B to ground is
guaranteed to be greater than 96k (C, I-Grade). 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 specified 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 high input resistance of the
receiver is maintained whether it is enabled or disabled,
powered or unpowered.
A ground plane layout is recommended. 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 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.
Supply Current
The unloaded static supply currents in these devices 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 load current
is 33mA, which is sourced by the positive voltage supply.
Power supply current increases with toggling data 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
RDIFF = 54Ω
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-duplex devices, DI and A/B should not be routed
near the driver or receiver outputs.
The logic inputs 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 driver termination also reduce glitches caused
by driver transitions.
Cable Length vs Data Rate
SUPPLY CURRENT (mA)
70
For a given data rate, the maximum transmission distance
is bounded by the cable properties. A 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
CL = 1000pF
60
50
40
CL = 100pF
30
20
0.1
1
10
DATA RATE (Mbps)
100
285012 F13
Figure 13. Supply Current vs Data Rate
285012fc
11
LTC2850/LTC2851/LTC2852
APPLICATIONS INFORMATION
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 LTC2850, LTC2851,
and LTC2852.
CABLE LENGTH (FT)
10k
1k
LTC2850/
LTC2851/LTC2852
MAX DATA RATE
100
RS485/RS422
MAX DATA RATE
10
10k
100k
1M
10M
DATA RATE (bps)
100M
285012 F14
Figure 14. Cable Length vs Data Rate
(RS485/RS422 Standard Shown in Solid Line)
TYPICAL APPLICATIONS
Failsafe “0” Application (Idle State = Logic “0”)
VCC
100k
I1
RO
R
B
A
DI
I2
“A”
“B”
D
LTC2850
285012 TA02
Multi-Node Network with End Termination Using the LTC2850 and LTC2854
R
D
LTC2850
R
D
LTC2850
R
R
TE = 3.3V
TE = 3.3V
D
D
LTC2854
LTC2854
285012 TA03
285012fc
12
LTC2850/LTC2851/LTC2852
PACKAGE DESCRIPTION
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698)
0.675 ±0.05
3.5 ±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
R = 0.115
TYP
5
3.00 ±0.10
(4 SIDES)
0.38 ± 0.10
8
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(NOTE 6)
(DD) DFN 1203
0.75 ±0.05
0.200 REF
4
0.25 ± 0.05
1
0.50 BSC
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-1)
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 TOP AND BOTTOM OF PACKAGE
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
TYP
0.38 ± 0.10
6
10
5
1
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
0.25 ± 0.05
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
0.50
BSC
2.38 ±0.05
(2 SIDES)
(DD) DFN 1103
0.75 ±0.05
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
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
285012fc
13
LTC2850/LTC2851/LTC2852
PACKAGE DESCRIPTION
MS8 Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660 Rev F)
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.254
(.010)
8
7 6 5
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0.52
(.0205)
REF
0° – 6° TYP
GAUGE PLANE
0.42 ± 0.038
(.0165 ± .0015)
TYP
0.65
(.0256)
BSC
1
0.53 ± 0.152
(.021 ± .006)
RECOMMENDED SOLDER PAD LAYOUT
DETAIL “A”
2 3
4
1.10
(.043)
MAX
0.86
(.034)
REF
0.18
(.007)
SEATING
PLANE
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.22 – 0.38
(.009 – .015)
TYP
0.65
(.0256)
BSC
0.1016 ± 0.0508
(.004 ± .002)
MSOP (MS8) 0307 REV F
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661 Rev E)
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
10 9 8 7 6
3.20 – 3.45
(.126 – .136)
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0.497 ± 0.076
(.0196 ± .003)
REF
0° – 6° TYP
GAUGE PLANE
1 2 3 4 5
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.1016 ± 0.0508
(.004 ± .002)
MSOP (MS) 0307 REV E
285012fc
14
LTC2850/LTC2851/LTC2852
PACKAGE DESCRIPTION
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
.050 BSC
7
8
.245
MIN
5
6
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
× 45°
(0.254 – 0.508)
3
2
4
.053 – .069
(1.346 – 1.752)
.008 – .010
(0.203 – 0.254)
.004 – .010
(0.101 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
NOTE:
1. DIMENSIONS IN
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
SO8 0303
S Package
14-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.337 – .344
(8.560 – 8.738)
NOTE 3
.045 ±.005
.050 BSC
14
N
12
11
10
9
8
N
.245
MIN
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
1
.030 ±.005
TYP
13
2
3
N/2
N/2
RECOMMENDED SOLDER PAD LAYOUT
1
.010 – .020
× 45°
(0.254 – 0.508)
.008 – .010
(0.203 – 0.254)
2
3
4
5
6
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. DIMENSIONS IN
.014 – .019
(0.355 – 0.483)
TYP
7
.050
(1.270)
BSC
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
S14 0502
285012fc
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.
15
LTC2850/LTC2851/LTC2852
TYPICAL APPLICATION
SLAVE
SLAVE
LTC2852
LTC2852
R
D
R
D
MASTER
SLAVE
120Ω
D
R
TE = 3.3V
TE = 3.3V
R
D
LTC2855
LTC2855
285012 TA04
Full Duplex Network Using the LTC2852 and LTC2855
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 Transceiver 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
LTC2854/LTC2855
3.3V 20Mbps RS485/RS422 Transceivers with Integrated Switchable 3.3V Operation, Integrated, Switchable, 120Ω Termination
Termination
Resistor, 25kV ESD (LTC2854), 15kV ESD (LTC2855)
LTC2856-1
20Mbps and Slew Rate-Limited, 15kV RS485/RS422 Transceiver
15kV ESD
LTC2859/LTC2861
20Mbps RS485/RS422 Transceiver with Integrated Switchable
Termination
Integrated, Switchable, 120Ω Termination Resistor, 15kV ESD
285012fc
16 Linear Technology Corporation
LT 0308 REV C • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2007