Datasheet

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LTC2850/LTC2851/LTC2852

285012fd

Typical applicaTion

FeaTures

applicaTions

DescripTion

3.3V 20Mbps RS485/RS422

Transceivers

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.

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.

LTC2850 at 20Mbps Into 54Ω

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

Low Power RS485/RS422 Transceiver

Level Translator

Backplane Transceiver

CC1

GND1

RO1

RE1

DE1

DI1

LTC2850

285012 TA01a

CC2

GND2

RO2

RE2

DE2

DI2

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

20ns/DIV

2V/DIV

285012 TA01b

A-B

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

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

Summary of content (18 pages)

PAGE 1
LTC2850/LTC2851/LTC2852 3.3V 20Mbps RS485/RS422 Transceivers Features n n n n n n n n n n n n Description 3.
PAGE 2
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..............................................
PAGE 3
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) MP = Military Temperature Range (–55°C to 125°C) PROD
PAGE 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 |VOD| Differential Driver Output Voltage R = ∞, VCC = 3V (Figure 1) R = 27Ω, VCC = 3V (Figure 1) R = 50Ω, VCC = 3.
PAGE 5
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.
PAGE 6
LTC2850/LTC2851/LTC2852 Test Circuits Y GND OR VCC DI Y + DRIVER VOD – R R GND OR VCC + – 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.
PAGE 7
LTC2850/LTC2851/LTC2852 Test Circuits RL Y VCC OR GND DI CL DRIVER VCC DE GND OR VCC DE Z CL VCC OR GND 285012 F05a tZLD, tZLSD VCC Y OR Z RL 1/2 VCC 0V VO VOL Z OR Y tLZD 1/2 VCC VOH 0.5V 0.5V 1/2 VCC 0V tZHD, tZHSD 285012 F05b tHZD, tSHDN Figure 5.
PAGE 8
LTC2850/LTC2851/LTC2852 Typical Performance Characteristics Receiver Skew vs Temperature Driver Propagation Delay vs Temperature Driver Skew vs Temperature 1.5 VAB = 1.5V CL = 15pF 0 16 0.5 PROP DELAY (ns) 1 18 RDIFF = 54Ω CL = 100pF 1.0 DRIVER SKEW (ns) RECEIVER SKEW (ns) 2 TA = 25°C. VCC = 3.3V, unless otherwise noted. 0 –0.5 –1.
PAGE 9
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.
PAGE 10
LTC2850/LTC2851/LTC2852 Block Diagram LTC2850 LTC2851 VCC VCC A (15kV) RO RE DE DI RECEIVER RO RECEIVER B (15kV) A (15kV) SLEEP/SHUTDOWN LOGIC AND DELAY B (15kV) Z (15kV) DRIVER DI DRIVER Y (15kV) 285012 BDa 285012 BDb GND GND LTC2852 VCC A (15kV) RO RECEIVER B (15kV) RE DE SLEEP/SHUTDOWN LOGIC AND DELAY Z (15kV) DI DRIVER Y (15kV) 285012 BDc GND 285012fd 10
PAGE 11
LTC2850/LTC2851/LTC2852 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.
PAGE 12
LTC2850/LTC2851/LTC2852 Applications Information 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. RDIFF = 54Ω SUPPLY CURRENT (mA) 70 CL = 1000pF 60 50 40 CL = 100pF Cable Length vs Data Rate 30 20 0.1 1 10 DATA RATE (Mbps) 100 285012 F13 Figure 13.
PAGE 13
LTC2850/LTC2851/LTC2852 Typical Applications Failsafe “0” Application (Idle State = Logic “0”) VCC 100k I1 RO R B A DI I2 “A” “B” D LTC2850 285012 TA02 Multinode Network with End Termination Using the LTC2850 and LTC2854 R D LTC2850 R D LTC2850 R R TE = 3.3V TE = 3.
PAGE 14
LTC2850/LTC2851/LTC2852 Package Description DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698 Rev C) 0.70 p0.05 3.5 p0.05 1.65 p0.05 2.10 p0.05 (2 SIDES) PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 2.38 p0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 p0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) R = 0.125 TYP 5 1.65 p 0.10 (2 SIDES) 0.75 p0.05 0.200 REF 0.40 p 0.10 8 4 0.25 p 0.05 (DD8) DFN 0509 REV C 1 0.50 BSC 2.38 p0.
PAGE 15
LTC2850/LTC2851/LTC2852 Package Description MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660 Rev F) 3.00 p 0.102 (.118 p .004) (NOTE 3) 0.889 p 0.127 (.035 p .005) 5.23 (.206) MIN 0.254 (.010) 7 6 5 0.52 (.0205) REF 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) DETAIL “A” 0o – 6o TYP GAUGE PLANE 3.20 – 3.45 (.126 – .136) 0.53 p 0.152 (.021 p .006) DETAIL “A” 0.42 p 0.038 (.0165 p .0015) TYP 8 0.65 (.0256) BSC 1 2 3 4 1.10 (.043) MAX 0.86 (.034) REF 0.
PAGE 16
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 .160 ±.005 5 6 .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.
PAGE 17
LTC2850/LTC2851/LTC2852 Revision History (Revision history begins at Rev D) REV DATE DESCRIPTION PAGE NUMBER D 05/10 Added military grade parts. 2, 3 285012fd 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.
PAGE 18
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.