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FEATURES

LTC2859/LTC2861 20Mbps RS485 Transceivers with Integrated Switchable Termination DESCRIPTION
The LTC(R)2859 and LTC2861 are low power, 20Mbps RS485/422 transceivers operating on 5V supplies. The receiver includes a logic-selectable 120 termination, one-eighth unit load supporting up to 256 nodes per bus, and a failsafe feature that guarantees a high output state under conditions of floating or shorted inputs. The driver features a logic-selectable low-EMI 250kbps operating mode, and 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 LTC2859 and LTC2861 to withstand 15kV (human body model) on the transceiver interface pins without latchup or damage.

Integrated, Logic-Selectable 120 Termination Resistor 20Mbps Max Data Rate No Damage or Latchup to ESD: 15kV HBM High Input Impedance Supports 256 Nodes 250kbps Low-EMI Mode Guaranteed Failsafe Receiver Operation Over the Entire Common Mode Range Current Limited Drivers and Thermal Shutdown Delayed Micropower Shutdown (5A Max) Power Up/Down Glitch-Free Driver Outputs Low Operating Current (900A Max in Receive Mode) Meets All TIA/EIA-485-A Specifications Available in 10-Pin 3mm x 3mm DFN, 12-Pin 4mm x 3mm DFN and 16-Pin SSOP Packages
APPLICATIONS

Low Power RS485/RS422 Transceiver Level Translator Backplane Transceiver
PRODUCT SELECTION GUIDE
PART NUMBER LTC2859 LTC2861 DUPLEX Half Full PACKAGE DFN-10 SSOP-16, DFN-12
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
LTC2859 RO RE TE DE DI SLO
2859/61 TA01
LTC2859 R RO RE TE DE Y D DI SLO LTC2859 120 2V/DIV 20ns/DIV Z Y-Z
R
LTC2859 at 20Mbps
DI
120 D
120
285961 TA02
R D
RO RE TE DE
DI
SLO
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LTC2859/LTC2861 ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (VCC) ................................... -0.3V to 7V Logic Input Voltages (RE, DE, DI, TE, SLO) ... -0.3V to 7V Interface I/O: A, B, Y, Z ...................................... (VCC -15V) to +15V (A-B) or (B-A) with Terminat or Enabled .................6V Receiver Output Voltage (RO) ........ -0.3V to (VCC +0.3V)
Operating Temperature (Note 4) LTC2859C, LTC2861C .............................. 0C to 70C LTC2859I, LTC2861I ............................. -40C to 85C Storage Temperature Range................... -65C to 125C Lead Temperature (Soldering, 10 sec) GN Package ...................................................... 300C
PIN CONFIGURATION
TOP VIEW TOP VIEW RO RO RE DE DI TE 1 2 3 4 5 11 10 VCC 9B 8A 7 SLO 6 GND RE DE DI TE GND DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN EXPOSED PAD (PIN 11) PCB GND CONNECTION TJMAX = 125C, JA = 43C/W JC = 3C/W 1 2 3 4 5 6 13 12 VCC 11 A 10 B 9 8 7 Z Y SLO RO RE DE DI TE GND NC NC 1 2 3 4 5 6 7 8 TOP VIEW 16 VCC 15 A 14 B 13 Z 12 Y 11 SLO 10 NC 9 NC
DE PACKAGE 12-LEAD (4mm x 3mm) PLASTIC DFN EXPOSED PAD (PIN 13) PCB GND CONNECTION TJMAX = 125C, JA = 43C/W JC = 4.3C/W
GN PACKAGE 16-LEAD (NARROW 0.150) PLASTIC SSOP TJMAX = 125C, JA = 110C/W JC = 40C/W
ORDER INFORMATION
LEAD FREE FINISH LTC2861CDE#PBF LTC2861IDE#PBF LTC2861CGN#PBF LTC2861IGN#PBF LTC2859CDD#PBF LTC2859IDD#PBF LEAD BASED FINISH LTC2861CDE LTC2861IDE LTC2861CGN LTC2861IGN TAPE AND REEL LTC2861CDE#TRPBF LTC2861IDE#TRPBF LTC2861CGN#TRPBF LTC2861IGN#TRPBF LTC2859CDD#TRPBF LTC2859IDD#TRPBF TAPE AND REEL LTC2861CDE#TR LTC2861IDE#TR LTC2861CGN#TR LTC2861IGN#TR PART MARKING* 2861 2861 2861 2861I LBNX LBNX PART MARKING* 2861 2861 2861 2861I PACKAGE DESCRIPTION 12-Lead (4mm x 3mm) Plastic DFN 12-Lead (4mm x 3mm) Plastic DFN 16-Lead Plastic SSOP 16-Lead Plastic SSOP 10-Lead (3mm x 3mm) Plastic DFN 10-Lead (3mm x 3mm) Plastic DFN PACKAGE DESCRIPTION 12-Lead (4mm x 3mm) Plastic DFN 12-Lead (4mm x 3mm) Plastic DFN 16-Lead Plastic SSOP 16-Lead Plastic SSOP TEMPERATURE RANGE 0C to 70C -40C to 85C 0C to 70C -40C to 85C 0C to 70C -40C to 85C TEMPERATURE RANGE 0C to 70C -40C to 85C 0C to 70C -40C to 85C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. 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/
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LTC2859/LTC2861 ELECTRICAL CHARACTERISTICS
SYMBOL Driver |VOD| Differential Driver Output Voltage R = , IO = 0mA, VCC = 4.5V (Figure 1) R = 27 (RS485), VCC = 4.5V (Figure 1) R = 50 (RS422), VCC = 4.5V (Figure 1) R = 27 or R = 50 (Figure 1)

The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 5V unless otherwise noted (Note 2).
PARAMETER CONDITIONS MIN TYP MAX VCC VCC VCC 0.2 UNITS V V V V
1.5 2.0
|VOD|
Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Driver Common Mode Output Voltage Change 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 Receiver Input Current (A, B)
VOC |VOC|
R = 27 or R = 50 (Figure 1) R = 27 or R = 50 (Figure 1)

3.0 0.2
V V
IOZD IOSD Receiver IIN2
DE = OV, VO = -7V, +12V (LTC2861 Only) -7V (Y or Z) 12 (Figure 2) DE = TE = 0V, VCC = 0V or 5V, VA or VB = 12V, Other at 0V DE = TE = 0V, VCC = 0V or 5V, VA or VB = -7V, Other at 0V

10 120 250 125 -100 0.2 25
A mA A A V mV V

VTH VTH VOH VOL IOZR RIN RTERM Logic VIH VIL IIN1 Supplies ISHDN ICCR ICCT ICCTS ICCL ICCRT
Receiver Differential Input Threshold Voltage Receiver Input Hysteresis Receiver Output HIGH Voltage Receiver Output LOW Voltage Receiver Three-State (High Impedance) Output Current on RO Receiver Input Resistance Receiver Input Terminating Resistor
-7V VCM 12 VCM = 0V I0 = -4mA, VID = 200mV, VCC = 4.5V I0 = 4mA, VID = -200mV, VCC = 4.5V RE = 5V, 0V VO VCC RE = 5V or 0V, DE = TE = 0V -7V VA = VB 12V TE = 5V, VAB = 2V, VB = -7, 0, 10V (Figure 7) DE, DI, RE, TE, SLO, VCC = 4.5V DE, DI, RE, TE, SLO, VCC = 4.5V DE, DI, RE, TE, SLO DE = 0V, RE = VCC, TE = 0V No Load, DE = 0V, RE = 0V, TE = 0V No Load, DE = VCC, RE = VCC, SLO = VCC, TE = 0V No Load, DE = VCC, RE = VCC, SLO = 0V, TE = 0V

2.4 0.4 1 96 108 125 120 156
V A k
Logic Input High Voltage Logic Input Low Voltage Logic Input Current Supply Current in Shutdown Mode Supply Current in Receive Mode Supply Current in Transmit Mode Supply Current in Transmit SLO Mode

2 0.8 0 0 540 630 670 660 640 10 5 900 1000 1100 1100 1180
V V A A A A A A A

Supply Current in Loopback Mode (Both No Load, DE = VCC, RE= 0V, SLO = VCC, TE Driver and Receiver Enabled) = 0V Supply Current in Termination Mode DE = 0V, RE = VCC, TE = VCC, SLO = VCC
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LTC2859/LTC2861 SWITCHING CHARACTERISTICS
SYMBOL fMAX tPLHD, tPHLD tPD tSKEWD tRD, tFD tZLD, tZHD, tLZD, tHZD tZHSD, tZLSD tSHDN PARAMETER Maximum Data Rate Driver Input to Output Driver Input to Output Difference |tPLHD-tPHLD| Driver Output Y to Output Z Driver Rise or Fall Time Driver Enable or Disable Time Driver Enable from Shutdown Time to Shutdown Driver in Normal Mode (SLO HIGH) Note 3 RDIFF = 54, CL = 100pF (Figure 3) RDIFF = 54, CL = 100pF (Figure 3) RDIFF = 54, CL = 100pF (Figure 3) RDIFF = 54, CL = 100pF (Figure 3) RL = 500, CL = 50pF RE = 0 (Figure 4) , RL = 500, CL = 50pF RE = VCC (Figure 4) , (DE = , RE = VCC) or (DE = 0, RE ) (Figure 4) Note 3 RDIFF = 54, CL = 100pF (Figure 3) RDIFF = 54, CL = 100pF (Figure 3) RDIFF = 54, CL = 100pF (Figure 3) RDIFF = 54, CL = 100pF (Figure 3) RL = 500, CL = 50pF RE = 0 (Figure 4) , RL = 500, CL = 50pF RE = 0 (Figure 4) , RL = 500, CL = 50pF RE = VCC (Figure 4) , (DE = 0, RE = ) or (DE = , RE = VCC) (Figure 4) CL = 15pF VCM = 1.5V, |VAB| = 1.5V, tR and , tF < 4ns (Figure 5) CL = 15pF (Figure 5) CL = 15pF (Figure 5) RL = 1k, CL =15pF DE = VCC (Figure 6) , DI = 0 or VCC RL = 1k, CL = 15pF DE = 0V (Figure 6) , DI = 0 or VCC VB = 0V, VAB = 2V, RE = VCC, DE = 0V (Figure 7)

The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 5V, TE = 0 unless otherwise noted (Note 2).
CONDITIONS MIN 20 10 1 1 4 50 6 6 12.5 70 8 100 TYP MAX UNITS Mbps ns ns ns ns ns s ns
Driver in SLO Mode (SLO LOW) fMAXS tPLHDS, tPHLDS tPDS tSKEWDS tRDS, tFDS tZHDS, tZLDS tLZDS, tHZDS tZHSDS, tZLSDS tSHDNS Receiver tPLHR, tPHLR tSKEWR tRR, tFR tZLR, tZHR, tLZR, tHZR tZHSR, tZLSR tRTEN, tRTZ Receiver Input to Output Differential Receiver Skew |tPLHR-tPHLR| Receiver Output Rise or Fall Time Receiver Enable/Disable Receiver Enable from Shutdown Termination Enable or Disable Time

Maximum Data Rate Driver Input to Output Driver Input to Output Difference |tPLHR-tPHLR| Driver Output A to Output B Driver Rise or Fall Time Driver Enable Time Driver Disable Time Driver Enable from Shutdown Time to Shutdown

250 0.95 50 200 0.9 1.5 500 500 1.5 300 70 8 500
kbps s ns ns s ns ns s ns
50 1 3
70 6 12.5 50 8 100
ns ns ns ns s s
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.. 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. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure.
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LTC2859/LTC2861 TEST CIRCUITS
Y GND DI OR VCC DRIVER Z + VOD - Y GND OR DI VCC IOSD DRIVER Z
R
R
+ VOC -
+ -
2859/61 F01-2
-7V to +12V
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
Y DI CL DRIVER Z RDIFF CL
DI
VCC OV
tPLHD, tPLHDS tSKEWD, tSKEWDS VO 1/2 VO
tPHLD, tPHLDS
Y, Z
(Y-Z)
90% 10%
0 tRD, tRDS
0
90% 10% tFD, tFDS
2859/61 F03
Figure 3. Driver Timing Measurement
RL Y VCC OR DI GND DRIVER Z DE CL RL CL
GND OR VCC
VCC DE 1/2 VCC OV VCC Y or Z VO VOL VOH
tZLD, tZLDS, tZLSD, tZLSDS 1/2 VCC
tLZD, tLZDS 0.5V 0.5V tHZD, tHZDS, tSHDN, tSHDNS
2859/61 F04
VCC OR GND
Z or Y
1/2 VCC OV tZHD, tZHDS, tZHSD, tZHSDS
Figure 4. Driver Enable and Disable Timing Measurement
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LTC2859/LTC2861 TEST CIRCUITS
VAB/2 VCM VAB/2 A B RECEIVER RO CL RO 0V A-B VAB 0V -VAB VCC VO 90% 10% tPLHR 1/2 VCC tRR tSKEWR = tPLHR - tPHLR
2859/61 F05
1/2 VCC
tPHLR 90% 10% tFR
Figure 5. Receiver Propagation Delay Measurements
0V OR VCC
A RECEIVER RO CL RE
RE RL VCC OR GND
VCC 0V VCC VO VOL VOH
tZLR, tZLSR
1/2 VCC tLZR 1/2 VCC 0.5V 0.5V tHZR
2859/61 F06
VCC OR 0V
B
RO
DI = 0V OR VCC
RO 0V tZHR, tZHSR
1/2 VCC
Figure 6. Receiver Enable/Disable Time Measurements
A RO RECEIVER
RTERM = VAB IA
VCC TE 1/2 VCC 0V IA 90% 10% tRTEN tRTZ
+ -
B
VAB
TE
+ -
VB
2859/61 F07
Figure 7. Termination Resistance and Timing Measurements
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LTC2859/LTC2861 TYPICAL PERFORMANCE CHARACTERISTICS
Receiver Skew vs Temperature
VAB = 1.5V CL = 15pF 2 RECEIVER SKEW (ns) 2 DRIVER SKEW (ns) 3
TA = 25C, VCC = 5V, unless otherwise noted. Driver Propagation Delay vs Temperature
18 16 DRIVER PROP DELAY (ns) 14 12 10 8 6 RDIFF = 54 CL = 100pF SLO = VCC
Driver Skew vs Temperature
RDIFF = 54 CL = 100pF SLO = VCC
1
1
0 0 -1 -40 -20
-40 -20
0
20 40 60 80 TEMPERATURE (C)
100 120
285961 G01
0
20 40 60 80 TEMPERATURE (C)
100 120
285961 G02
4 -40 -20
0
20
40
60
80
100 120
285961 G03
TEMPERATURE (C)
RTERM vs Temperature
135 130 4 OUTPUT VOLTAGE (V) 125 RESISTANCE () 120 115 110 105 100 95 -40 -20 0 0 20 40 60 80 TEMPERATURE (C) 100 120
285961 G04
Driver Output Low/High Voltage vs Output Current
5 VOH 4 OUTPUT VOLTAGE (V) 5
Driver Differential Output Voltage vs Temperature
R=
3
3
R = 100 R = 54
2 VOL
2
1
1
0
10
40 30 20 50 OUTPUT CURRENT (mA)
60
70
285961 G05
0 -40 -20
0
20 40 60 80 TEMPERATURE (C)
100 120
285961 G06
Receiver Output Voltage vs Output Current (Source and Sink)
5 SOURCE 65 4 OUTPUT VOLTAGE (V) 60 PROP DELAY (ns) 3 55 50 45 40 35 SINK 0 0 1 3 4 2 OUTPUT CURRENT (mA) 5
285961 G07
Receiver Propagation Delay vs Temperature
70 VAB = 1.5V CL = 15pF SUPPLY CURRENT (mA) 60 50 40
Supply Current vs Data Rate
R = 54
R = 100 30 20 10 R= 0 0.1
2
1
30 -40 -20
0
20 40 60 80 TEMPERATURE (C)
100 120
285961 G08
10 1 DATA RATE (Mbps)
100
285961 G09
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LTC2859/LTC2861 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 valid 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.
TE (Pin 5): Internal Termination Resistance Enable. A high input will connect a termination resistor (120 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. SLO (Pins 7/7/11): Driver Slew Rate Control. A low input will force the driver into a reduced slew rate mode. Y (Pins -/8/12): Positive Driver Output for LTC2861. Z (Pins -/9/13): Negative Driver Output for LTC2861. B (Pins 9/10/14): Negative Receiver Input (and Negative Driver Output for LTC2859). A (Pins 8/11/15): Positive Receiver Input (and Positive Driver Output for LTC2859). VCC (Pins 10/12/16): Positive Supply. 4.5V < VCC < 5.5V. Bypass with 0.1F ceramic capacitor.
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LTC2859/LTC2861 FUNCTION TABLES
LTC2859
LOGIC INPUTS DE 0 0 0 0 1 1 1 1 RE 0 0 1 1 0 0 1 1 TE 0 1 0 1 0 1 0 1 MODE Receive Receive with Term Shutdown Term Only Transmit with Receive Transmit with Receive and Term Transmit Transmit with Term A, B RIN RIN RIN RIN Driven Driven Driven Driven RO Enabled Enabled Hi-Z Hi-Z Enabled Enabled Hi-Z Hi-Z TERMINATOR Off On Off On Off On Off On
LTC2861
LOGIC INPUTS DE 0 0 0 0 1 1 1 1 RE 0 0 1 1 0 0 1 1 TE 0 1 0 1 0 1 0 1 MODE Receive Receive with Term Shutdown Term Only Transmit with Receive Transmit with Receive and Term Transmit Transmit with Term A, B RIN RIN RIN RIN RIN RIN RIN RIN YZ , Hi-Z Hi-Z Hi-Z Hi-Z Driven Driven Driven Driven RO Enabled Enabled Hi-Z Hi-Z Enabled Enabled Hi-Z Hi-Z TERMINATOR Off On Off On Off On Off On
BLOCK DIAGRAMS
LTC2859
A (15kV) 120
LTC2861
A (15kV) 120
RE DE
SLEEP/SHUTDOWN LOGIC AND DELAY
RE DE
SLEEP/SHUTDOWN LOGIC AND DELAY
TE
TE
RO
RECEIVER B (15kV)
RO
RECEIVER B (15kV)
SLO
SLO Z (15kV) Y (15kV)
2859/61 BD
DI
DRIVER
DI
DRIVER
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LTC2859/LTC2861 APPLICATIONS INFORMATION
Driver The driver provides full RS485 and RS422 compatibility. When enabled, if DI is high, Y-Z is positive for the full duplex device (LTC2861) and A-B is positive for the halfduplex device (LTC2859). When the driver is disabled, both outputs are highimpedance. For the full duplex LTC2861, 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 LTC2859, 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 maximum current in this condition is 250mA. If the pin voltage exceeds about 10V, current limit folds back to about half of the peak value to reduce overall power dissipation and avoid damaging the part. The LTC2859/LTC2861 also feature thermal shutdown protection that disables the driver, terminator, and receiver in case of excessive power dissipation. SLO Mode: Slew Limiting for EMI Emissions Control The LTC2859/LTC2861 feature a logic-selectable reducedslew mode (SLO mode) that softens the driver output edges to control the high frequency EMI emissions from equipment and data cables. The reduced slew rate mode is entered by taking the SLO pin low, where the data rate is limited to about 250kbps. Slew limiting also mitigates the adverse effects of imperfect transmission line termination caused by stubs or mismatched cables. Figures 8a and 8b show the LTC2861 driver outputs in normal and SLO mode with their corresponding frequency spectrums operating at 250kbps. SLO mode significantly reduces the high frequency harmonics.
Y, Z Y-Z Y-Z
1V/DIV
2s/DIV
10dB/DIV
1.25MHz/DIV
285961 F08a
Driver Output at 125kHz into 100 Resistor
Frequency Spectrum of the Same Signal
Figure 8a. Driver Output in Normal Mode
Y, Z
Y-Z
Y-Z
1V/DIV
2s/DIV
10dB/DIV
1.25MHz/DIV
285961 F08b
Driver Output at 125kHz into 100 Resistor
Frequency Spectrum of the Same Signal
285961fb
Figure 8b. Driver Output in SLO Mode
10
LTC2859/LTC2861 APPLICATIONS INFORMATION
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). The LTC2859/LTC2861 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 (externally or internally), but not driven for more than about 3s. The delay prevents signal zero crossings from being interpreted as shorted inputs and causing RO to go high inadvertently. 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 Hi-Z with leakage of less than 1A 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 when the termination is disabled. This is 8X higher than the requirements for 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 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. 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 LTC2859/LTC2861 are the first RS485 transceivers to offer integrated switchable termination resistors on the receiver input pins. This provides the tremendous advantage of being able to easily change, through logic control, the proper line termination for optimal performance when configuring transceiver networks. When the TE pin is high, the termination resistor is enabled and the differential resistance from A to B is 120. Figure 10 shows the I/V characteristics between pins A and B with the termination resistor enabled and disabled.
A >96k 60
TE 60
2859/61 F09
B
>96k
Figure 9. Equivalent Input Resistance into A and B (on the LTC2859, Valid if Driver is Disabled)
Figure 10. Curve Trace Between A and B with Termination Enabled and Disabled
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LTC2859/LTC2861 APPLICATIONS INFORMATION
The resistance is maintained over the entire RS485 common mode range of -7V to +12V as shown in Figure 11.
RESISTANCE () 150
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. Supply Current The unloaded static supply currents in the LTC2859/ LTC2861 are very low --typically under 700A for all modes of operation without the internal terminator enabled. 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 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 LTC2859/ LTC2861. 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 3). High Speed Considerations A ground plane layout is recommended for the LTC2859/ LTC2861. 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 (LTC2861) 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 LTC2861, DI and A/B should not be routed near the driver or receiver outputs. The logic inputs of the LTC2859/LTC2861 have 50mV 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
140
130
120
110 -10
-5 5 10 0 COMMON MODE VOLTAGE (V)
15
285961 F11
Figure 11. Termination Resistance vs Common Mode Voltage
140 120 100 80 60 40 20 PHASE MAGNITUDE
0 -5 PHASE (DEGREES)
MAGNITUDE ()
-10
-15
-20
-25 0 10-1 100 101 FREQUENCY (MHz) 102
285961 F12
Figure 12. Termination Magnitude and Phase vs Frequency
75 70 65 60 55 50
RDIFF = 54
CURRENT (mA)
CL = 1000pF
CL = 100pF
45 102
103 104 DATA RATE (kbps)
105
285961 F13
Figure 13. Supply Current vs Data Rate
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LTC2859/LTC2861 APPLICATIONS INFORMATION
from a driver transition may exceed the hysteresis levels on the logic and data inputs 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 line termination also reduces glitches caused by driver transitions. Cable Length 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 standard 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 standard. The dashed lines at 250kbps and 20Mbps show the maximum data rates of the LTC2859/LTC2861 in LowEMI and normal modes, respectively.
10k
CABLE LENGTH (FT)
1k
LOW-EMI MODE MAX DATA RATE
100 RS485 MAX DATA RATE 10 10k 100k
NORMAL MODE MAX DATA RATE
1M 10M DATA RATE (bps)
100M
285961 F14
Figure 14. Cable Length vs Data Rate (RS485 Standard Shown in Solid Lines)
PACKAGE DESCRIPTION
DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05 0.38 0.10 10
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 PIN 1 TOP MARK (SEE NOTE 6)
3.00 0.10 (4 SIDES)
1.65 0.10 (2 SIDES)
(DD10) DFN 1103
5 0.200 REF 0.50 BSC 2.38 0.05 (2 SIDES) 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
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
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LTC2859/LTC2861 PACKAGE DESCRIPTION
DE/UE Package 12-Lead Plastic DFN (4mm x 3mm)
(Reference LTC DWG # 05-08-1695)
4.00 0.10 (2 SIDES) 0.70 0.05 3.30 0.05 1.70 0.05 PIN 1 TOP MARK PACKAGE (NOTE 6) OUTLINE 0.25 0.05 2.50 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 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 0.00 - 0.05 0.200 REF 0.50 BSC 0.75 0.05 R = 0.05 TYP 3.00 0.10 (2 SIDES)
7
R = 0.115 TYP
0.40 0.10 12
3.60 0.05 2.20 0.05
3.30 0.10 1.70 0.10 PIN 1 NOTCH R = 0.20 OR 0.35 x 45 CHAMFER 1 0.50 BSC
(UE12/DE12) DFN 0806 REV D
6 0.25 0.05 2.50 REF
BOTTOM VIEW--EXPOSED PAD
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
GN Package 16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.045 .005
.189 - .196* (4.801 - 4.978) 16 15 14 13 12 11 10 9
.009 (0.229) REF
.254 MIN
.150 - .165
.229 - .244 (5.817 - 6.198)
.150 - .157** (3.810 - 3.988)
.0165 .0015
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1 .015 .004 x 45 (0.38 0.10)
.007 - .0098 (0.178 - 0.249) 0 - 8 TYP .0532 - .0688 (1.35 - 1.75)
23
4
56
7
8
.004 - .0098 (0.102 - 0.249)
.016 - .050 (0.406 - 1.270)
NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE
.008 - .012 (0.203 - 0.305) TYP
.0250 (0.635) BSC
GN16 (SSOP) 0204
*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
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LTC2859/LTC2861 TYPICAL APPLICATIONS
Multi-Node Network with End Termination Using LTC2859
TE = 0V
TE = 0V
D R R
D
LTC2859
LTC2859
LTC2859 R TE = 5V
LTC2859 R TE = 5V
D
D
2859/61 TA04
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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
LTC2859/LTC2861 TYPICAL APPLICATION
Failsafe "0" Application (Idle State = Logic "0")
VCC 100k RO I1 R LTC2859 B "A"
120 DI I2 D
A
"B"
2859/61 TA03
RELATED PARTS
PART NUMBER LTC485 LTC491 LTC1480 LTC1483 LTC1485 LTC1487 LTC1520 LTC1535 LTC1685 LT1785 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 10Mbaud Operation Up to 256 Transceivers on the Bus Channel-to-Channel Skew 400ps (Typ) 2500VRMS Isolation in Surface Mount Package Propagation Delay Skew 500ps (Typ) 60V Tolerant, 15kV ESD
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16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT 0108 REV B * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2006

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