Datasheet

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LTM2881

2881fg

For more information www.linear.com/LTM2881

TYPICAL APPLICATION

DESCRIPTION

Complete Isolated

RS485/RS422 µModule

Transceiver + Power

The LT M

2881 is a complete galvanically isolated full-du-

plex RS485/RS422 µModule

(micromodule) transceiver.

No external components are required. A single supply

powers both sides of the interface through an integrated,

isolated, low noise, efficient 5V output DC/DC converter.

Coupled inductors and an isolation power transformer

provide 2500V

RMS

of isolation between the line transceiver

and the logic interface. This device is ideal for systems

where the ground loop is broken allowing for large com

mon mode voltage variation. Uninterrupted communica-

tion is guaranteed for common mode transients greater

than 30kV/μs.

Maximum data rates are 20Mbps or 250kbps in slew

limited mode. T

ransmit data, DI and receive data, RO, are

implemented with event driven low jitter processing. The

receiver has a one-eighth unit load supporting up to 256

nodes per bus. A logic supply pin allows easy interfacing

with different logic levels from 1.62V to 5.5V, independent

of the main supply.

Enhanced ESD protection allows this part to withstand up

to ±15kV (human body model) on the transceiver interface

pins to isolated supplies and ±10kV through the isolation

barrier to logic supplies without latch-up or damage.

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

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

Isolated Half-Duplex RS485 μModule Transceiver

FEATURES

APPLICATIONS

RS485/RS422 Transceiver: 2500V

RMS

for 1 Minute

UL Recognized

File #E151738

Isolated DC Power: 5V at Up to 200mA

No External Components Required

20Mbps or Low EMI 250kbps Data Rate

High ESD: ±15kV HBM on Transceiver Interface

High Common Mode Transient Immunity: 30kV/μs

Integrated Selectable 120Ω Termination

3.3V (LTM2881-3) or 5.0V (LTM2881-5) Operation

1.62V to 5.5V Logic Supply Pin for Flexible Digital Interface

Maximum Continuous Working Voltage: 560V

PEAK

High Input Impedance Failsafe RS485 Receiver

Current Limited Drivers and Thermal Shutdown

Compatible with TIA/EIA-485-A and PROFIBUS

High Impedance Output During Internal Fault Condition

Low Current Shutdown Mode (< 10µA)

General Purpose CMOS Isolated Channel

Small, Low Profile (15mm × 11.25mm)

Surface Mount BGA and LGA Packages

Isolated RS485/RS422 Interface

Industrial Networks

Breaking RS485 Ground Loops

Isolated PROFIBUS-DP Networks

LTM2881 Operating Through 35kV/μs CM Transients

2881 TA01

TWISTED-PAIR

CABLE

AVAILABLE CURRENT:

150mA (LTM2881-5)

100mA (LTM2881-3)

CC2

GND GND2

3.3V (LTM2881-3)

5V (LTM2881-5)

LTM2881

PWR

ISOLATION BARRIER

2881 TA01a

500V/DIV

50ns/DIV

1V/DIV

MULTIPLE SWEEPS

OF COMMON MODE

TRANSIENTS

Summary of content (24 pages)

PAGE 1
LTM2881 Complete Isolated RS485/RS422 µModule Transceiver + Power DESCRIPTION FEATURES n n RS485/RS422 Transceiver: 2500VRMS for 1 Minute UL Recognized File #E151738 Isolated DC Power: 5V at Up to 200mA No External Components Required 20Mbps or Low EMI 250kbps Data Rate High ESD: ±15kV HBM on Transceiver Interface High Common Mode Transient Immunity: 30kV/μs Integrated Selectable 120Ω Termination 3.3V (LTM2881-3) or 5.0V (LTM2881-5) Operation 1.62V to 5.
PAGE 2
LTM2881 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VCC to GND................................................... –0.3V to 6V VCC2 to GND2................................................ –0.3V to 6V VL to GND..................................................... –0.3V to 6V Interface Voltages (A, B, Y, Z) to GND2......................... VCC2 –15V to 15V (A-B) with Terminator Enabled...............................±6V Signal Voltages ON, RO, DI, DE, RE, TE, DOUT to GND.......................... –0.
PAGE 3
LTM2881 ORDER INFORMATION PART NUMBER LTM2881CY-3#PBF LTM2881IY-3#PBF LTM2881HY-3#PBF LTM2881HY-3 LTM2881MPY-3#PBF LTM2881MPY-3 LTM2881CY-5#PBF LTM2881IY-5#PBF LTM2881HY-5#PBF LTM2881HY-5 LTM2881MPY-5#PBF LTM2881MPY-5 LTM2881CV-3#PBF LTM2881IV-3#PBF LTM2881HV-3#PBF LTM2881CV-5#PBF LTM2881IV-5#PBF LTM2881HV-5#PBF INPUT VOLTAGE PAD OR BALL FINISH PART MARKING DEVICE FINISH CODE SAC305 (RoHS) 3V to 3.6V SnPb (63/37) SAC305 (RoHS) SnPb (63/37) SnPb (63/37) SAC305 (RoHS) SnPb (63/37) 3V to 3.
PAGE 4
LTM2881 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V, GND = GND2 = 0V, ON = VL unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX l l 3.0 4.5 3.3 5.0 3.6 5.5 l 1.62 UNITS Power Supply VCC VCC Supply Voltage VL VL Supply Voltage 5.
PAGE 5
LTM2881 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V, GND = GND2 = 0V, ON = VL unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Logic VIL Logic Input Low Voltage 1.62V ≤ VL ≤ 5.5V l Logic Input High Voltage DIN SLO DI, TE, DE, ON, RE: VL ≥ 2.35V 1.62V ≤ VL < 2.35V l l 0.67•VCC2 2 V V l l 0.67•VL 0.
PAGE 6
LTM2881 SWITCHING CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V, GND = GND2 = 0V, ON = VL unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN tZLD , tZHD , tLZD , tHZD Driver Output Enable or Disable Time RL = 500Ω, CL = 50pF (Figure 5) l tPLHR tPHLR Receiver Input to Output CL = 15pF, VCM = 2.5V, |VAB| = 1.
PAGE 7
LTM2881 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V unless otherwise noted. 2.0 80 1.5 1.5 75 1.0 0.5 0 DRIVER PROP DELAY (ns) 2.0 1.0 0.5 0 –0.5 –0.5 –1.0 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 –1.0 –50 125 –25 0 25 50 75 TEMPERATURE (°C) 100 4.5 126 4.0 124 3.5 122 120 118 116 1.5 0.
PAGE 8
LTM2881 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, LTM2881-3 VCC = 3.3V, LTM2881-5 VCC = 5.0V, VL = 3.3V unless otherwise noted. 6 LTM2881-3, VCC = 3.
PAGE 9
LTM2881 PIN FUNCTIONS LOGIC SIDE (VCC , VL, GND) ISOLATED SIDE (VCC2, GND2) DOUT (Pin A1): General Purpose Logic Output. Logic output connected through isolation path to DIN . Under the condition of an isolation communication failure DOUT is in a high impedance state. DIN (Pin L1): General Purpose Isolated Logic Input. Logic input on the isolated side relative to VCC2 and GND2. A logic high on DIN will generate a logic high on DOUT. A logic low on DIN will generate a logic low on DOUT.
PAGE 10
LTM2881 BLOCK DIAGRAM VCC 2.2µF VCC2 5V REG ISOLATED DC/DC CONVERTER 2.2µF VL 2.2µF A RO RX B RE ISOLATED COMM INTERFACE DE ISOLATED COMM INTERFACE 120Ω DI Y DX ON Z SLO TE DIN DOUT GND GND2 2881 BD = LOGIC SIDE COMMON = ISOLATED SIDE COMMON TEST CIRCUITS Y GND OR VL DI Y + DRIVER VOD – Z R R GND OR VL + – DI IOSD DRIVER VOC Z 2881 F01 –7V TO 12V 2881 F02 Figure 1. Driver DC Characteristics Figure 2.
PAGE 11
LTM2881 TEST CIRCUITS DI Y DI VL tPLHD 0V tPHLD tSKEWD CL DRIVER RDIFF Y, Z VOD 1/2 VOD CL Z 90% 2881 F04a (Y-Z) 10% 0 0 90% 10% tRD tFD 2881 F04b Figure 4. Driver Timing Measurement RL Y VL OR GND DI CL GND OR VCC2 RL Z 1/2 VL 0V tZLD VCC2 Y OR Z DRIVER DE VL DE CL VCC2 OR GND 2881 F05a tLZD 1/2 VCC2 0.5V 0.5V 1/2 VCC2 Z OR Y 0V tZHD 2881 F05b tHZD Figure 5.
PAGE 12
LTM2881 TEST CIRCUITS VL RE 0V OR VCC2 B VCC2 OR 0V 1/2 VL 0V A RL RO RECEIVER VL OR GND CL RE tZLR VL RO 1/2 VL VOL RO VOH 0.5V 0.5V 1/2 VL 0V 2881 F07a tLZR 2881 F07b tZHR tHZR Figure 7. Receiver Enable/Disable Time Measurements IA A RO RTE = + – RECEIVER VAB IA TE VAB VL 1/2 VL 0V IA B + – TE tRTEN tRTZ 90% 10% VB 2881 F08 Figure 8.
PAGE 13
LTM2881 APPLICATIONS INFORMATION Overview The LTM2881 µModule transceiver provides a galvanicallyisolated robust RS485/RS422 interface, powered by an integrated, regulated DC/DC converter, complete with decoupling capacitors. A switchable termination resistor is integrated at the receiver input to provide proper termination to the RS485 bus. The LTM2881 is ideal for use in networks where grounds can take on different voltages.
PAGE 14
LTM2881 Y-Z 10dB/DIV Y-Z 10dB/DIV APPLICATIONS INFORMATION 0 6.25 FREQUENCY (MHz) 12.5 0 6.25 FREQUENCY (MHz) 12.5 2881 F09b 2881 F09a Figure 9a. Frequency Spectrum SLO Mode 125kHz Input Figure 9b. Normal Mode Frequency Spectrum 125kHz Input reduce EMI emissions from equipment and data cables. The reduced slew rate mode is entered by taking the SLO pin low to GND2, where the data rate is limited to about 250kbps.
PAGE 15
LTM2881 APPLICATIONS INFORMATION Switchable Termination Proper cable termination is very important for signal fidelity. If the cable is not terminated with its characteristic impedance, reflections will distort the signal waveforms. The integrated switchable termination resistor provides logic control of the line termination for optimal perfor mance when configuring transceiver networks. Supply Current The static supply current is dominated by power delivered to the termination resistance.
PAGE 16
LTM2881 APPLICATIONS INFORMATION PROFIBUS Applications The LTM2881 can be used in PROFIBUS-DP networks where isolation is required. The standard PROFIBUS termination differs from RS485 termination and is shown in Figure 15. If used in this way, the internal termination should remain disabled (TE low). The 390Ω resistors in Figure 15 pre-bias the bus so that when the line is not driven, the receiver delivers a high output.
PAGE 17
LTM2881 APPLICATIONS INFORMATION TECHNOLOGY Figure 16a. Low EMI Demo Board Layout Figure 16b. Low EMI Demo Board Layout (DC1746A), Top Layer Figure 16c. Low EMI Demo Board Layout (DC1746A), Inner Layer 1 2881fg For more information www.linear.
PAGE 18
LTM2881 APPLICATIONS INFORMATION Figure 16d. Low EMI Demo Board Layout (DC1746A), Inner Layer 2 Figure 16e. Low EMI Demo Board Layout (DC1746A), Bottom Layer 60 DETECTOR = QuasiPeak 50 RBW = 120kHz, VBW = 300kHz SWEEP TIME = 17sec 40 # OF POINTS = 501 dBµV/m 30 20 10 0 –10 –20 –30 DC1746A-B CISPR 22 CLASS 8 LIMIT 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) 2881 F17 Figure 17. Low EMI Demo Board Emissions 2881fg 18 For more information www.linear.
PAGE 19
LTM2881 APPLICATIONS INFORMATION The PCB layout in Figures 16a to 16e show the low EMI demo board for the LTM2881. The demo board uses a combination of EMI mitigation techniques, including both embedded PCB bridge capacitance and discrete GND to GND2 capacitors. Two safety rated type Y2 capacitors are used in series, manufactured by Murata, part number GA342QR7GF471KW01L. The embedded capacitor effectively suppresses emissions above 400MHz, whereas the discrete capacitors are more effective below 400MHz.
PAGE 20
LTM2881 TYPICAL APPLICATIONS VCC VCC VCC ISOLATION BARRIER RE TE DE DI RE TE Y DE Z DI DIN GND FAULT RO B DOUT LTM2881 PWR VL A RO 330k VCC LTM2881 B Y Z GND GND2 A ISOLATION BARRIER VL GND2 2881 F20 2881 F19 Figure 20. Full-Duplex RS485 Connection Figure 19. Isolated System Fault Detection VCC 1.
PAGE 21
1.905 3.175 SUGGESTED PCB LAYOUT TOP VIEW 0.000 aaa Z 0.630 ±0.025 Ø 32x 0.635 PACKAGE TOP VIEW E 0.635 4 1.905 3.175 4.445 Y X D For more information www.linear.com/LTM2881 6.350 5.080 0.000 5.080 6.350 aaa Z 2.45 – 2.55 SYMBOL A A1 A2 b b1 D E e F G aaa bbb ccc ddd eee NOM 3.42 0.60 2.82 0.75 0.63 15.0 11.25 1.27 12.70 8.89 DIMENSIONS 0.15 0.10 0.20 0.30 0.15 MAX 3.62 0.70 2.92 0.90 0.66 NOTES DETAIL B PACKAGE SIDE VIEW TOTAL NUMBER OF BALLS: 32 MIN 3.22 0.50 2.72 0.60 0.
PAGE 22
4 For more information www.linear.com/LTM2881 3.175 SUGGESTED PCB LAYOUT TOP VIEW 1.905 PACKAGE TOP VIEW 11.25 BSC 0.635 Y X 6.350 5.080 0.000 5.080 6.350 DETAIL c 15.00 BSC aaa Z 2.400 – 2.600 eee S X Y 0.290 – 0.350 SUBSTRATE DETAIL C 0.630 ±0.025 Ø 32x DETAIL B eee S X Y DETAILS OF PAD #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE PAD #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE 4 SYMBOL TOLERANCE aaa 0.10 bbb 0.10 eee 0.05 6.
PAGE 23
LTM2881 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 3/10 Changes to Features, Description and Typical Application Add BGA Package to Pin Configuration, Order Information and Package Description Sections 1 2, 19 Changes to LGA Package in Pin Configuration Section 2 Changes to Electrical Characteristics Section 3 Changes to Graphs G09, G13, G14 6, 7 Update to Pin Functions 8 Update to Applications Information 12 Change to X-Axis on Figures 9a and 9b 13 Update to Supply Current Sect
PAGE 24
LTM2881 TYPICAL APPLICATION VCCC VCCA VCC LTM2881 PWR VL ISOLATION BARRIER CABLE SHIELD OR GROUND RETURN Y Y Z Z GND2 A VCC2 DE DI GND GND2 A RE TE C Z GND B VL RO PWR GND2 DI B Y DE A B VCC1 RE TE A PWR ISOLATION BARRIER RO VCC LTM2881 ISOLATION BARRIER GND DI DE TE RE RO VCC VL VCCB LTM2881 2881 F23 B B Figure 23.