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LTC2850/LTC2851/LTC2852 3.3V 20Mbps RS485/RS422 Transceivers FEATURES
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DESCRIPTION
The LTC(R)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. 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 LTC2850 LTC2851 LTC2852 DUPLEX Half Full Full PACKAGE SO-8, MSOP-8, DFN-8 SO-8, MSOP-8, DFN-8 SO-14, MSOP-10, DFN-10
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 125C (H-Grade) Guaranteed Failsafe Receiver Operation Over the Entire Common Mode Range Current Limited Drivers and Thermal Shutdown Delayed Micropower Shutdown: 5A Maximum (C, I-Grade) Power Up/Down Glitch-Free Driver Outputs Low Operating Current: 370A Typical in Receive Mode Compatible with TIA/EIA-485-A Specifications Available in 8-Pin and 10-Pin 3mm x 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
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 RO1 RE1 DE1 DI1 D GND1 2V/DIV LTC2850 RO2 RE2 DE2 DI2 D GND2
285012 TA01a
LTC2850 at 20Mbps Into 54
VCC1 DI RT A
R
B A-B
R
VCC2
RT
20ns/DIV
285012 TA01b
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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................................................. 0C to 70C LTC285xI .............................................. -40C to 85C LTC285xH .......................................... -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) MSOP ............................................................... 300C
PIN CONFIGURATION
LTC2850 TOP VIEW TOP VIEW RO RE DE DI 1 2 3 4 9 8 7 6 5 VCC B A GND RO RE DE DI 1 2 3 4 TOP VIEW 8 7 6 5 VCC B A GND RO RE DE DI 1 2 3 4 8 7 6 5 VCC B A GND
DD PACKAGE 8-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 150C, JA = 43C/W, JC = 3C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB LTC2851 TOP VIEW
MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 150C, JA = 200C/W, JC = 40C/W
S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 150C, JA = 150C/W, JC = 39C/W
TOP VIEW VCC RO DI GND 1 2 3 4 9 8 7 6 5 A B Z Y VCC RO DI GND 1 2 3 4 TOP VIEW 8 7 6 5 A B Z Y VCC RO DI GND 1 2 3 4 8 7 6 5 A B Z Y
DD PACKAGE 8-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 150C, JA = 43C/W, JC = 3C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 150C, JA = 200C/W, JC = 40C/W
S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 150C, JA = 150C/W, JC = 39C/W
LTC2852 TOP VIEW TOP VIEW RO RE DE DI GND 1 2 3 4 5 11 10 VCC 9A 8B 7Z 6Y RO RE DE DI GND 1 2 3 4 5 10 9 8 7 6 VCC A B Z Y NC 1 RO 2 RE 3 DE 4 DI 5 GND 6 GND 7
TOP VIEW 14 VCC 13 NC 12 A 11 B 10 Z 9 8 Y NC
MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 150C, JA = 120C/W, JC = 45C/W
DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 150C, JA = 43C/W, JC = 3C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
S PACKAGE 14-LEAD PLASTIC SO TJMAX = 150C, JA = 88C/W, JC = 37C/W
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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 (0C to 70C) I = Industrial Temperature Range (-40C to 85C) H = Automotive Temperature Range (-40C to 125C) 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 LTC2850 LTC2851 LTC2852 PART MARKING 2850/I/H, LTCQD, LCQC 2851/I/H, LTCWF, LCWD 2852CS/IS/HS, LTCRX, LCRY DUPLEX Half Full Full LOW POWER SHUTDOWN MODE Yes No Yes PACKAGE SO-8, MSOP-8, DFN-8 SO-8, MSOP-8, DFN-8 SO-14, MSOP-10, DFN-10
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LTC2850/LTC2851/LTC2852 ELECTRICAL CHARACTERISTICS
SYMBOL Driver |VOD| Differential Driver Output Voltage R = , VCC = 3V (Figure 1) R = 27, VCC = 3V (Figure 1) R = 50, VCC = 3.13V (Figure 1)
l l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 3.3V unless otherwise noted. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX VCC VCC VCC 0.2 UNITS V V V V
1.5 2
|VOD|
Difference in Magnitude of Driver Differential R = 27 or 50 (Figure 1) Output Voltage for Complementary Output States Driver Common Mode Output Voltage Difference in Magnitude of Driver Common Mode Output Voltage for Complementary Output States Driver Three-State (High Impedance) Output Current on Y and Z Maximum Driver Short-Circuit Current R = 27 or 50 (Figure 1) R = 27 or 50 (Figure 1)
VOC |VOC|
l l
3 0.2
V V
IOZD IOSD Receiver IIN
DE = 0V, (Y or Z) = -7V, 12V (LTC2852) -7V (Y or Z) 12V (Figure 2)
l
10 180 -250 250 300 125 -100 250 -145 96 125
A mA mA A A A A k
l l l l l l
Receiver Input Current (A, B)
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) 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)
RIN
Receiver Input Resistance
RE = VCC or 0V, DE = TE = 0V, VIN = -7V, -3V, 3V, 7V, 12V (Figure 3) (C, I-Grade) RE = VCC or 0V, DE = TE = 0V, VIN = -7V, -3V, 3V, 7V, 12V (Figure 3) (H-Grade)
l
48
125
k
VTH VTH VOH VOL IOZR IOSR Logic VIH VIL IINL
Receiver Differential Input Threshold Voltage -7V B 12V Receiver Input Hysteresis Receiver Output High Voltage Receiver Output Low Voltage Receiver Three-State (High Impedance) Output Current on RO Receiver Short-Circuit Current Logic Input High Voltage Logic Input Low Voltage Logic Input Current B = 0V I(RO) = -4mA, A-B = 200mV, VCC = 3V I(RO) = 4mA, A-B = -200mV, VCC = 3V RE = VCC, 0V RO VCC (LTC2850, LTC2852) 0V RO VCC VCC = 3.6V VCC = 3V
l
0.2 25 2.4 0.4 1 85 2 0.8 0 10
V mV V V A mA V V A
l l l l l l l
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LTC2850/LTC2851/LTC2852 ELECTRICAL CHARACTERISTICS
SYMBOL Supplies ICCS Supply Current in Shutdown Mode DE = 0V, RE = VCC, LTC2850, LTC2852 (C and I-Grade) LTC2850, LTC2852 (H-Grade) DE = 0V, RE = 0V (LTC2850, LTC2852) No Load, DE = VCC, RE = VCC (LTC2850, LTC2852) No Load, DE = VCC, RE = 0V
l l l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 3.3V unless otherwise noted. (Note 2)
PARAMETER CONDITIONS MIN TYP 0 0 370 450 450 MAX 5 15 900 1000 1000 UNITS A A A A A
ICCR ICCT ICCTR
Supply Current in Receive Mode Supply Current in Transmit Mode Supply Current with Both Driver and Receiver Enabled
SWITCHING CHARACTERISTICS
SYMBOL Driver fMAX tPD tSKEWD tRD, tFD tZLD, tZHD, tLZD, tHZD Maximum Data Rate Driver Input to Output Difference |tPLHD - tPHLD| Driver Output Y to Output Z Driver Rise or Fall Time Driver Enable or Disable Time PARAMETER
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 3.3V, unless otherwise noted. (Note 2)
CONDITIONS (Note 3) RDIFF = 54, CL = 100pF (Figure 4) RDIFF = 54, CL = 100pF (Figure 4) RDIFF = 54, CL = 100pF (Figure 4) RDIFF = 54, CL = 100pF (Figure 4) RL = 500, CL = 50pF RE = 0V (Figure 5) , (LTC2850, LTC2852) RL = 500, CL = 50pF RE = VCC (Figure 5) , (LTC2850, LTC2852) RL = 500, CL = 50pF (DE = , RE = VCC) , or (DE = 0V, RE = ) (Figure 5) (LTC2850, LTC2852) CL = 15pF VCM = 1.5V, |VAB| = 1.5V, , tR and tF < 4ns (Figure 6) CL = 15pF (Figure 6) CL = 15pF (Figure 6) RL =1k, CL =15pF DE = VCC (Figure 7) , (LTC2850, LTC2852) RL = 1k, CL = 15pF DE = 0V (Figure 7) , (LTC2850, LTC2852)
l l l l l l l l
MIN 20
TYP
MAX
UNITS Mbps
tPLHD, tPHLD Driver Input to Output
10 1 1 4
50 6 6 12.5 70 8 100
ns ns ns ns ns s ns
tZHSD, tZLSD Driver Enable from Shutdown tSHDN Time to Shutdown
Receiver tPLHR, tPHLR Receiver Input to Output tSKEWR tRR, tFR tZLR, tZHR, tLZR, tHZR Differential Receiver Skew |tPLHR - tPHLR| Receiver Output Rise or Fall Time Receiver Enable/Disable
l l l l l
50 1 3
70 6 12.5 50 8
ns ns ns ns s
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 105C. 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 150C. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure.
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LTC2850/LTC2851/LTC2852 TEST CIRCUITS
Y GND OR VCC DI Y R IOSD DRIVER
DRIVER
+
VOD
-
R
Z
VOC
+ -
GND OR VCC
DI
Z
+ -
285012 F02
-7V TO 12V
285012 F01
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
IIN
A OR B RECEIVER B OR A
285012 F03
VIN
+ -
V RIN = IN IIN
Figure 3. Receiver Input Current and Input Resistance
VCC DI Y DI CL DRIVER RDIFF CL Z
285012 F04a
tPLHD 0V tSKEWD
tPHLD
Y, Z
VO
1/2 VO
90% (Y-Z) 10% 0 tRD 0
90% 10% tFD
285012 F04b
Figure 4. Driver Timing Measurement
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LTC2850/LTC2851/LTC2852 TEST CIRCUITS
VCC Y VCC OR GND DI CL DRIVER RL DE Z CL VCC OR GND
285012 F05a
RL
GND OR VCC
DE 0V VCC Y OR Z VOL VOH Z OR Y 0V VO
1/2 VCC tZLD, tZLSD 1/2 VCC tLZD 0.5V 0.5V tHZD, tSHDN
285012 F05b
1/2 VCC tZHD, tZHSD
Figure 5. Driver Enable and Disable Timing Measurements
tR VAB A-B -VAB CL
285012 F06a
tF 90%
VAB/2 VCM VAB/2
A RECEIVER B RO
90% 10%
0 tPLHR
10% tPHLR 1/2 VCC 90% 10% tFR
285012 F06b
VCC RO 0 VO
90% 1/2 VCC 10% tRR
tSKEWR = |tPLHR - tPHLR|
Figure 6. Receiver Propagation Delay Measurements
RE 0V OR VCC A RECEIVER VCC OR 0V B RE RO CL RL VCC OR GND RO
VCC 1/2 VCC 0V VCC VO VOL VOH tZLR, tZLSR 1/2 VCC tLZR 0.5V 0.5V
285012 F07b
DI = 0V OR VCC
285012 F07a
RO 0V tZHR, tZHSR
1/2 VCC tHZR
Figure 7. Receiver Enable/Disable Time Measurements
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LTC2850/LTC2851/LTC2852 TYPICAL PERFORMANCE CHARACTERISTICS
Receiver Skew vs Temperature
2 VAB = 1.5V CL = 15pF 1.5 1.0 RECEIVER SKEW (ns) DRIVER SKEW (ns) 1 0.5 0 -0.5 -1.0 -1 -40 -20 -1.5 -40 -20 PROP DELAY (ns)
TA = 25C. VCC = 3.3V unless otherwise noted. Driver Propagation Delay vs Temperature
18 16 14 12 10 8 6 4 -40 -20 RDIFF = 54 CL = 100pF
Driver Skew vs Temperature
RDIFF = 54 CL = 100pF
0
0
20 40 60 80 TEMPERATURE (C)
100 120
285012 G01
0
20 40 60 80 TEMPERATURE (C)
100 120
285012 G02
0
20 40 60 80 TEMPERATURE (C)
100 120
285012 G03
Driver Output Short-Circuit Current vs Temperature
150 OUTPUT SHORT-CIRCUIT CURRENT (mA) 140 OUTPUT VOLTAGE (V) 130 120 110 100 90 80 -40 -20 SOURCE VOUT = 0V SINK VOUT = 3.3V 3.5 3.0
Driver Output Low/High Voltage vs Output Current
3.5 3.0 VOH 2.5 2.0 1.5 1.0 0.5 0 VOL OUTPUT VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5
Driver Differential Output Voltage vs Temperature
RDIFF = RDIFF = 100
RDIFF = 54
0
20 40 60 80 TEMPERATURE (C)
100 120
285012 G04
0
10
30 40 50 20 OUTPUT CURRENT (mA)
60
70
0 -40 -20
0
20 40 60 80 TEMPERATURE (C)
100 120
285012 G06
285012 G05
Receiver Output Voltage vs Output Current (Source and Sink)
3.5 3.0 OUTPUT VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5 0 0 1 3 4 2 OUTPUT CURRENT (mA) 5 6
285012 G07
Receiver Propagation Delay vs Temperature
70 65 PROP DELAY (ns) 60 55 50 45 40 35 -40 -20 SUPPLY CURRENT (mA) 60 50
Supply Current vs Data Rate
CL = 100pF
SOURCE
RDIFF = 54 40 30 20 RDIFF = 10 0 0.1 RDIFF = 100
SINK
0
20 40 60 80 TEMPERATURE (C)
100 120
285012 G08
10 1 DATA RATE (Mbps)
100
285012 G09
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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. RE: Receiver Enable. A low enables the receiver. A high input forces the receiver output into a high impedance state. 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. 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. GND: Ground. Y: Noninverting Driver Output for LTC2851 and LTC2852. High-impedance when driver disabled or unpowered. Z: Inverting Driver Output for LTC2851 and LTC2852. Highimpedance when driver disabled or unpowered. A: Noninverting Receiver Input (and Noninverting Driver Output for LTC2850). Impedance is >96k in receive mode or unpowered. B: Inverting Receiver Input (and Inverting Driver Output for LTC2850). Impedance is >96k in receive mode or unpowered. VCC: Positive Supply. 3V < VCC < 3.6V. Bypass with 0.1F ceramic capacitor. Exposed Pad: Ground. The exposed pads on the DFN packages must be soldered to ground.
FUNCTION TABLES
LTC2850
Logic Inputs DE 0 0 1 1 RE 0 1 0 1 Mode Receive Shutdown Transceive Transmit A, B RIN RIN Driven Driven RO Driven High-Z Driven High-Z
LTC2852
Logic Inputs DE 0 0 1 1 RE 0 1 0 1 Mode Receive Shutdown Transceive Transmit A, B RIN RIN RIN RIN YZ , High-Z High-Z Driven Driven RO Driven High-Z Driven High-Z
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LTC2850/LTC2851/LTC2852 BLOCK DIAGRAM
LTC2850
VCC
LTC2851
VCC
LTC2852
VCC
A (15kV) RO RECEIVER RO RECEIVER B (15kV) RE DE A (15kV) SLEEP/SHUTDOWN LOGIC AND DELAY B (15kV) Z (15kV) DI DRIVER DI DRIVER Y (15kV) DI DRIVER RE DE RO RECEIVER
A (15kV) B (15kV)
SLEEP/SHUTDOWN LOGIC AND DELAY
Z (15kV)
Y (15kV)
285012 BDa
285012 BDb
285012 BDc
GND
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 10A 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 1A for voltages within the supply range.
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LTC2850/LTC2851/LTC2852 APPLICATIONS INFORMATION
Receiver Input Resistance 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. Supply Current The unloaded static supply currents in these devices are very low, typically under 500A 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 120 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 70 60 50 40 30 20 0.1 1 10 DATA RATE (Mbps) 100
285012 F13
High Speed Considerations A ground plane layout is recommended. A 0.1F 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. 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/s when transitioning. Good supply decoupling and proper driver termination also reduce glitches caused by driver transitions. Cable Length vs Data Rate
RDIFF = 54
CL = 1000pF
CL = 100pF
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
SUPPLY CURRENT (mA)
Figure 13. Supply Current vs Data Rate
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LTC2850/LTC2851/LTC2852 APPLICATIONS INFORMATION
10k
CABLE LENGTH (FT)
1k LTC2850/ LTC2851/LTC2852 MAX DATA RATE 100 RS485/RS422 MAX DATA RATE 10 10k 100k 1M 10M DATA RATE (bps) 100M
285012 F14
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.
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 RO I1 R B "A"
A DI I2 D LTC2850
"B"
285012 TA02
Multi-Node Network with End Termination Using the LTC2850 and LTC2854
R
D
R
D
LTC2850
LTC2850
R TE = 3.3V
R TE = 3.3V
D LTC2854 LTC2854
D
285012 TA03
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LTC2850/LTC2851/LTC2852 PACKAGE DESCRIPTION
DD Package 8-Lead Plastic DFN (3mm x 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 0.38 0.10 8
3.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6)
1.65 0.10 (2 SIDES)
(DD) DFN 1203
0.200 REF
0.75 0.05
4 0.25 0.05 2.38 0.10 (2 SIDES)
1 0.50 BSC
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 x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05 10 0.38 0.10
3.50 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 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 PIN 1 TOP MARK (SEE NOTE 6)
3.00 0.10 (4 SIDES)
1.65 0.10 (2 SIDES)
(DD) DFN 1103
5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES)
1
0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD
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13
LTC2850/LTC2851/LTC2852 PACKAGE DESCRIPTION
MS8 Package 8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660 Rev F)
0.889 0.127 (.035 .005) 3.00 0.102 (.118 .004) (NOTE 3) 0.52 (.0205) REF
8
7 65
5.23 (.206) MIN
3.20 - 3.45 (.126 - .136)
0.254 (.010)
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE 4)
GAUGE PLANE
0.42 0.038 (.0165 .0015) TYP
0.65 (.0256) BSC
DETAIL "A" 0.18 (.007)
1 0.53 0.152 (.021 .006) 1.10 (.043) MAX
23
4 0.86 (.034) REF
RECOMMENDED SOLDER PAD LAYOUT
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) 10 9 8 7 6 0.497 0.076 (.0196 .003) REF
0.889 0.127 (.035 .005)
5.23 (.206) MIN
3.20 - 3.45 (.126 - .136)
0.254 (.010) GAUGE PLANE
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE 4)
0.50 0.305 0.038 (.0197) (.0120 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
12345 0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) 1.10 (.043) MAX 0.86 (.034) REF
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
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14
LTC2850/LTC2851/LTC2852 PACKAGE DESCRIPTION
S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.045 .005 .050 BSC
8 .189 - .197 (4.801 - 5.004) NOTE 3 7 6 5
.245 MIN
.160 .005 .228 - .244 (5.791 - 6.197)
.150 - .157 (3.810 - 3.988) NOTE 3
.030 .005 TYP
RECOMMENDED SOLDER PAD LAYOUT .010 - .020 x 45 (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 0- 8 TYP
1
2
3
4
.053 - .069 (1.346 - 1.752)
.004 - .010 (0.101 - 0.254)
.016 - .050 (0.406 - 1.270)
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)
.014 - .019 (0.355 - 0.483) TYP
.050 (1.270) BSC
SO8 0303
S Package 14-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.045 .005 .050 BSC
N
.337 - .344 (8.560 - 8.738) NOTE 3 14 13 12 11 10 9 8
.245 MIN
N
.160 .005
.228 - .244 (5.791 - 6.197)
1 2 3 N/2
.150 - .157 (3.810 - 3.988) NOTE 3 N/2
.030 .005 TYP
RECOMMENDED SOLDER PAD LAYOUT
1
.010 - .020 x 45 (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 0 - 8 TYP
2
3
4
5
6
7
.053 - .069 (1.346 - 1.752)
.004 - .010 (0.101 - 0.254)
.016 - .050 (0.406 - 1.270)
NOTE: 1. DIMENSIONS IN
.014 - .019 (0.355 - 0.483) TYP
.050 (1.270) BSC
S14 0502
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)
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 LTC2852 R D R SLAVE LTC2852 D
MASTER
120
SLAVE
R TE = 3.3V
D
TE = 3.3V D LTC2855 LTC2855
285012 TA04
R
Full Duplex Network Using the LTC2852 and LTC2855
RELATED PARTS
PART NUMBER LTC485 LTC491 LTC1480 LTC1483 LTC1485 LTC1487 LTC1520 LTC1535 LTC1685 LT1785 LTC2854/LTC2855 LTC2856-1 LTC2859/LTC2861 DESCRIPTION Low Power RS485 Interface Transceiver Differential Driver and Receiver Pair 3.3V Ultralow Power RS485 Transceiver Ultralow Power RS485 Low EMI Transceiver Differential Bus Transceiver Ultralow Power RS485 with Low EMI, Shutdown and High Input Impedance 50Mbps Precision Quad Line Receiver Isolated RS485 Full-Duplex Transceiver 52Mbps RS485 Transceiver with Precision Delay 60V Fault Protected RS485 Transceiver COMMENTS ICC = 300A (Typ) ICC = 300A 3.3V Operation Controlled Driver Slew Rate 10Mbps Operation Up to 256 Transceiver on the Bus Channel-to-Channel Skew 400ps (Typ) 2500VRMS Isolation in Surface Mount Package Propagation Delay Skew 500ps (Typ) 60V Tolerant, 15kV ESD
3.3V 20Mbps RS485/RS422 Transceivers with Integrated Switchable 3.3V Operation, Integrated, Switchable, 120 Termination Termination Resistor, 25kV ESD (LTC2854), 15kV ESD (LTC2855) 20Mbps and Slew Rate-Limited, 15kV RS485/RS422 Transceiver 20Mbps RS485/RS422 Transceiver with Integrated Switchable Termination 15kV ESD Integrated, Switchable, 120 Termination Resistor, 15kV ESD
285012fc
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0308 REV C * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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