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LTC2859/LTC2861

285961fc

20Mbps RS485 Transceivers

with Integrated Switchable

Termination

The LT C

2859 and LTC2861 are low power, 20Mbps

RS485/422 transceivers operating on 5V supplies. The

receiver includes a logic-selectable 120Ω termination,

one-eighth unit load supporting up to 256 nodes per bus

(C-, I-grades), 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.

Low Power RS485/RS422 Transceiver

Level Translator

Backplane Transceiver

Integrated, Logic-Selectable 120Ω Termination

Resistor

20Mbps Max Data Rate

No Damage or Latchup to ESD: ±15kV HBM

High Input Impedance Supports 256 Nodes

(C-, I-Grades)

Operation Up to 105°C (LTC2859H)

250kbps Low-EMI Mode

Guaranteed Failsafe Receiver Operation Over the

Entire Common Mode Range

Current Limited Drivers and Thermal Shutdown

Delayed Micropower Shutdown (5µA Max)

Power Up/Down Glitch-Free Driver Outputs

Low Operating Current (900µA Max in Receive Mode)

Meets All TIA/EIA-485-A Specifications

Available in 10-Pin 3mm × 3mm DFN, 12-Pin

4mm × 3mm DFN and 16-Pin SSOP Packages

LTC2859 at 20Mbps

PART NUMBER DUPLEX PACKAGE

LTC2859 Half DFN-10

LTC2861 Full SSOP-16, DFN-12

Typical applicaTion

FeaTures

applicaTions

DescripTion

proDucT selecTion GuiDe

L, LT , LT C , LT M, Linear Technology, the Linear logo and µModule are registered trademarks of

Linear Technology Corporation. All other trademarks are the property of their respective owners.

285961 TA02

20ns/DIV2V/DIV

Y–Z

SLO

2859/61 TA01

LTC2859

120Ω

SLO

LTC2859

120Ω

RERO TE DE DI SLO

LTC2859

120Ω

Summary of content (18 pages)

PAGE 1
LTC2859/LTC2861 20Mbps RS485 Transceivers with Integrated Switchable Termination Description Features n n n n n n n n n n n n n Integrated, Logic-Selectable 120Ω Termination Resistor 20Mbps Max Data Rate No Damage or Latchup to ESD: ±15kV HBM High Input Impedance Supports 256 Nodes (C-, I-Grades) Operation Up to 105°C (LTC2859H) 250kbps Low-EMI Mode Guaranteed Failsafe Receiver Operation Over the Entire Common Mode Range Current Limited Drivers and Thermal Shutdown Delayed Micropower Shutdown (5µA Max)
PAGE 2
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 Terminator Enabled...................6V Receiver Output Voltage (RO).........–0.3V to (VCC +0.3V) Operating Temperature (Note 4) LTC2859C, LTC2861C............................... 0°C to 70°C LTC2859I, LTC2861I.................
PAGE 3
LTC2859/LTC2861 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 5V unless otherwise noted (Note 2). SYMBOL PARAMETER CONDITIONS MIN |VOD| Differential Driver Output Voltage R = ∞, IO = 0mA, VCC = 4.5V (Figure 1) R = 27Ω (RS485), VCC = 4.5V (Figure 1) R = 50Ω (RS422), VCC = 4.
PAGE 4
LTC2859/LTC2861 Switching Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 5V, TE = 0 unless otherwise noted (Note 2).
PAGE 5
LTC2859/LTC2861 Test Circuits Y GND DI OR VCC DRIVER Z Y R + VOD – R GND OR DI VCC + VOC – IOSD DRIVER Z + – –7V to +12V 2859/61 F01-2 Figure 1. Driver DC Characteristics Figure 2. Driver Output Short-Circuit Current DI Y DI DRIVER RDIFF tPLHD, tPLHDS OV CL CL VCC VO Y, Z tSKEWD, tSKEWDS tPHLD, tPHLDS 1/2 VO Z 90% 10% (Y-Z) 0 0 tRD, tRDS 90% 10% tFD, tFDS 2859/61 F03 Figure 3.
PAGE 6
LTC2859/LTC2861 test circuits ±VAB/2 A-B A VCM 0V –VAB RO RECEIVER B VAB VCC RO CL ±VAB/2 0V tPLHR VO 90% 10% 1/2 VCC 1/2 VCC tRR tPHLR 90% 10% tFR tSKEWR = tPLHR – tPHLR 2859/61 F05 Figure 5. Receiver Propagation Delay Measurements 0V OR VCC RE A RECEIVER VCC OR 0V RL RO CL B VCC OR GND RO RE RO DI = 0V OR VCC VCC 0V VCC VOL VOH tZLR, tZLSR 1/2 VCC tLZR VO 1/2 VCC 0.5V 0.5V 1/2 VCC 0V tZHR, tZHSR tHZR 2859/61 F06 Figure 6.
PAGE 7
LTC2859/LTC2861 Typical Performance Characteristics Receiver Skew vs Temperature Driver Propagation Delay vs Temperature Driver Skew vs Temperature 3 18 RDIFF = 54Ω CL = 100pF SLO = VCC 16 DRIVER PROP DELAY (ns) VAB = 1.5V CL = 15pF 2 TA = 25°C, VCC = 5V, unless otherwise noted.
PAGE 8
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.
PAGE 9
LTC2859/LTC2861 Function Tables LTC2859 LOGIC INPUTS DE RE TE MODE A, B RO TERMINATOR 0 0 0 Receive RIN Enabled Off 0 0 1 Receive with Term RIN Enabled On 0 1 0 Shutdown RIN Hi-Z Off 0 1 1 Term Only RIN Hi-Z On 1 0 0 Transmit with Receive Driven Enabled Off 1 0 1 Transmit with Receive and Term Driven Enabled On 1 1 0 Transmit Driven Hi-Z Off 1 1 1 Transmit with Term Driven Hi-Z On LTC2861 LOGIC INPUTS DE RE TE MODE A, B Y, Z RO TERMINATOR
PAGE 10
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 10µA over the entire common mode range of –7V to +12V.
PAGE 11
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 3µs.
PAGE 12
LTC2859/LTC2861 applications information 150 140 RESISTANCE (Ω) 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. The termination resistor cannot be enabled by TE if the device is unpowered or in thermal shutdown mode. Supply Current 120 110 –10 The logic inputs of the LTC2859/LTC2861 have 50mV of hysteresis to provide noise immunity.
PAGE 13
LTC2859/LTC2861 Applications Information 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.
PAGE 14
LTC2859/LTC2861 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.125 TYP 6 3.00 ±0.10 (4 SIDES) 0.40 ±0.10 10 1.65 ±0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.
PAGE 15
LTC2859/LTC2861 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695 Rev D) 0.70 ±0.05 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 2.50 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) 7 R = 0.115 TYP 0.40 ±0.10 12 R = 0.
PAGE 16
LTC2859/LTC2861 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) .045 ±.005 16 15 14 13 12 11 10 9 .254 MIN .009 (0.229) REF .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ±.0015 .150 – .157** (3.810 – 3.988) .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ±.004 × 45° (0.38 ±0.10) .007 – .0098 (0.178 – 0.249) .
PAGE 17
LTC2859/LTC2861 Revision History (Revision history begins at Rev C) REV DATE DESCRIPTION C 3/12 Added H-grade Order Information and Electrical Characteristics parameters PAGE NUMBER 2, 3, 4 Revised Receiver Input Resistance section 11 Replaced Figure 12 12 Added Termination Resistor restriction information 12 285961fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 18
LTC2859/LTC2861 Typical Application Failsafe “0” Application (Idle State = Logic “0”) VCC 100kΩ RO LTC2859 R I1 B 120Ω DI I2 A D "A" "B" 2859/61 TA03 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC2854/LTC2855 3.3V 20Mbps RS485/RS422 Transceivers with Integrated Switchable Termination Up to ±25kV HBM ESD, 125°C Operation LTC2856/LTC2857/ 5V 20Mbps and Slew Rate Limited 15kV RS485/RS422 LTC2858 Transceivers ±15kV ESD, 125°C Operation LTC2850/LTC2851/ 3.