Telefunken LVDS M-LVDS as an alternative to RS-485 422

Telefunken LVDS/M-LVDS as an alternative to RS-485/422

Why is LVDS attractive ? • For short haul (<50 m) LVDS offers a huge improvement in bandwidth • LVDS provides significant power savings • LVDS generates much less EMI • LVDS is a standard I/O in FPGA and ASIC libraries simplifying translation • Telefunken LVDS has extended common mode equaling the -7 to +12 V of RS-485 2

Pervasive LVDS LOGIC “ 1” Close spacing of differential pair and opposite currents minimize EMI 3. 5 m. A 350 m. V 100 3. 5 m. A LOGIC “ 0” Noise coupled onto both lines cancels thus maintaining the differential voltage and boosting noise immunity 3 LVDS is used extensively for reliable, low power, mid-range performance

“Common Mode” 2. 4 V 1. 4 V Common Mode 400 m. V Tx Rx Voltage Range where the Rx is guaranteed to operate 1. 0 V GND In noisy or distributed applications, there can be significant variation 4 in local “GND” potential due to return resistance or ground bounce.

Common Mode Example Eg: Automotive LVDS Tx LVDS Rx R Value of R changes over vehicle life Chasis Gnd “B” Several Volts of potential may develop between A & B Chasis Gnd “A” 5

Extended Common Mode 2. 4 V Industry LVDS Spec Guarantees Operation Between Ground and 2. 4 V >1 V of noise or Ground Potential Difference at Rx Causes Fault !!! Telefunke extends the mode to -7 t same as 1 V GND @ Tx GND @ Rx

Extended Common Mode 12 V 5 V 2. 4 V LVDS TI Extended Common Mode LVDS Telefunken Extended Common Mode LVDS RS-485 0 V - 4 V - 7 V 7

Robust Telefunken LVDS • Telefunken LVDS is manufactured using our in-house proprietary Silicon-on. Insulator process. This provides: – Extended common mode -7 to +12 V – Complete immunity to Latch-up – Minimal leakage and consistent operation up to ~150 C – 8 KV ESD 8

Silicon on Insulator (SOI) Process Technology SOI eliminates parasitics and leakage paths for a very robust and quiet signal path. Latch-up immune and excellent high-temp performance (used for extended common mode LVDS) Si. O 2 Insulator SOI Conventional bulk substrate with parasitic PNs 9

TF 048 Icc Leakage Tests m. A Degrees C No increase in leakage above 150 C 10

TF 048 VT threshold NOTE: VTH (max) is, Vcc = 3. 6 V (max) Common mode = 12 V (max) SPEC m. V NOTE: VTH (min) is, Vcc = 3. 0 V (min) Common mode = -7 V (min) Degrees C Worst case thresholds stay close to 0 V above 150 C 11

LVDS Features LVDS EIA/TIA-644 A Internal Termination Ext Common Mode -4 to +5 Fairchild X X Telefunken X X X Texas Instruments X X Maxim Robust Latch-up Free SOI X National Ext Common Mode -7 to +12 V 12

Evaluation Kit Extended Common Mode Eval Board includes 2 separate ground planes with LVDS connections configured via Cat 5 e or ribbon cable 13

M-LVDS

M-LVDS Features Smooth and balanced edges essential for driving backplanes (tr/tf ~2 ns) Must drive ~ 500 m. V Vod into distributed loads between 30 and 50 ohms (glitchfree) 50 Rx Common Mode spec is -1 V to 3. 4 V 15

M-LVDS constant VOD M-LVDS maintains constant output VOD as load varies

M-LVDS Receiver Thresholds HIGH FAILSAFE LOW TYPE 1 LOW TYPE 2

M-LVDS Type 2 Receiver – “Wired Or” Type 2 Receivers with offset can provide “Wired. Or” function for control signals. Floating bus has 0 V differential and M-LVDS type 2 Rx produces LOW output. Any driver can pull HI to interrupt

RS-485 and LVDS Specifications and Electricals

Driver Comparison

Receiver Comparison

Topologies Point to Point Note : One Tx & Rx, terminated as close to the Rx as possible. Provides cleanest environment capable of the highest performance, datarate & jitter Suitable technologies – RS-485, RS-422, LVDS 22

RS-485 – Extended Common Mode LVDS Comparison VOD RS-485 IOD (amplitude) EX CM LVDS VOS (offset) (drive) 250 -450 m. V 1. 125 to 1. 375 V 2. 5 to 4. 5 m. A -1 to 3 V 28 to 93 m. A 1. 5 to 5 Volts Rise/Fall (typical) Datarate (typical) VID Common Mode . 5 ns DC to 1000 Mbps . 1 to 1 Volts -7 to +12 Volts 5 to 50 ns DC to 10 Mbps . 4 to 5 Volts - 7 to +12 Volts 23

Pt to pt Translation RS-485/422 to Extended CM LVDS 22Ω RS-485 Resistor-divider network guarantees LVDS Vin amplitude of between 300 m. V and 1 Volt 11Ω TF 048 22Ω Common mode of -7 to +12 V meets RS-485 spec 24

Topologies Multi-drop, Multi-point Multiple Rx (multi-drop) and/or multiple Tx (multipoint) Note : termination typically at each end of transmission line, eg 100Ω for 50Ω effective load. Suitable technologies – (capable of driving multiple distributed loads) – RS-485, M-LVDS 25

RS-485 – Multi-drop LVDS Comparison VOD VOS IOD (amplitude) (offset) (drive) M-LVDS 480 -650 m. V . 3 to 2. 1 V 9 to 13 m. A RS-485 1. 5 to 5 Volts -1 to 3 V 28 to 93 m. A Rise/Fall (typical) Datarate (typical) VID Common Mode 1. 5 ns DC to 250 Mbps . 1 to 2. 4 Volts -1 to 3. 4 Volts 5 to 50 ns DC to 10 Mbps . 4 to 5 Volts - 7 to +12 Volts 26

Multidrop Translation RS-485 to M-LVDS RS-485 43Ω TF 176 43Ω 18Ω 43Ω TF 176 Need to assess common mode, M-LVDS -1 to 3. 4 V 27

Summary Comparing RS-485 and LVDS/M-LVDS • LVDS offers the following advantages: – – Higher datarate (at distances up to 50 m) Significant Power savings Significantly less EMI generation Simplified interface with FPGAs & ASICs • Telefunken LVDS matches the RS-485 common mode and is on latch-up free SOI • Telefunken LVDS is an excellent alternative for short haul point-to-point links – Voltage divider termination needed if RS-485 driver used • Telefunken M-LVDS is an alternative for multi-drop applications – Common mode and voltage divider termination/M-LVDS drive strength needs to be evaluated for mixed RS-485/M-LVDS network. 28