Noise Immunity Transients and ESD Practical Design Considerations

Noise Immunity Transients and ESD Practical Design Considerations prepared by Prof. George Slack (EE) Copyright © 2006 Rochester Institute of Technology All rights reserved. EDGE™

noise immunity • Circuit noise immunity is the ability of a device or component to operate in the presence of noise disturbance. • Electro Static Discharge is the sudden discharge (i. e. transients, surge). To the circuit, this is a rapid high voltage, low current situation. EDGE™

When is Noise Immunity design needed? • Senior Design I – Paper Design wks 1 -8 • Senior Design II – Prototype device testing wks 1 - 3. – Pre-integration testing with lab equipment DUT (device under test). Wks 3 - 6 EDGE™

Where does noise get into electronics? • 6. 4. 1 Sources * • • through ground connections and loops through power supply connections through signal inputs through inadvertent ESD – (human touch, lightning) • through Inductive devices (motors) • Electronic Instrumentation Design, Kim R. Fowler EDGE™

How does noise get into electronics? Energy Coupling (Conductive, Inductive, Capacitive) • EMI - Current surges (Electro. Magnetic Interference) An electrical disturbance in a system due to natural phenomena, low-frequency waves from electromechanical devices or high-frequency waves (RFI) from chips and other electronic devices. Allowable limits are governed by the FCC. RFI – high impedance devices requiring very limited current. (Radio Frequency Interference) High-frequency electromagnetic waves that emanate from electronic devices such as chips. If the source is sufficiently strong this can enter your circuit. EDGE™

ESD and unwanted signals • • • Fatal to Electronics: Inadvertent user misuse. Extreme cases of user abuse and solutions: – Bridge to block reverse polarity, – Schottky diode: very fast switching times and low forward voltage drop. As low as 0. 15 volts for low ma applications. – Zener diode across the input. – Circuit breaker – GFI EDGE™

Bare exposure to a CMOS gate Reduce Transients Protect from? • Misuse during debug and testing. • ESD and reverse polarity – Solution: Diode circuits to protect against • reduce transients – Component Specification Sheets – Solution: Low pass filter EDGE™

Polarity Protection (+) + Schottky diode 1 N 5822 or 1 N 5817 – (–) 1 N 4001 Input Port + Input Port – see 7. 4. 1 page 238, MOSFET solution EDGE™

Over-voltage Protection Fuse (+) (–) + input port – Zener diode 1 N 5339 (5. 6 V for a 5. 0 V input) EDGE™

Over-voltage Protection for Digital Inputs EDGE™

Minimize Bandwith One solution: Lowpass Filter EDGE™

Knowing Your Design Specification 1. If considering various output devices, review various manufactures specification sheets. 2. Current (i. e. CMOS versus TTL ). 3. Control Voltage (Vdd vary from 1. 5 VDC to 12 VDC typically) 4. Needed minimum Signal Transient Response. 5. RLC loads (dangerous current and voltage spikes) 6. Apply to Thevenin Equivalent Circuits – Source electronics – Device being driven EDGE™

Harness -Twisted Pair When purchasing harness cable: • Unshielded Twisted Pair (UTP) • Shielded Twisted Pair (STP) Study the manufacturer’s Specification to match to your needs. Practical Design Considerations http: //www. cirris. com/testing/twisted_pair/twist. html EDGE™

Harness Signal Response Design Considerations: data rate, distance, noise, parasitic capacitance, reflections. 1. Frequency Response/ Rise Time needs – DC to 100 khz Open Wire – DC to 40 MB/s Ribbon Cable (less than 3’) • • SCSI, SPI-3 applications http: //www. csee. umbc. edu/~plusquel/650/slides/ribbon_cables. pdf – DC to 300 mhz Twisted Pair - unshielded, ribbon – DC to 100/1000 MB/s 10/ 1000 Base. T ethernet Cat 5 minimum spec. RJ 45 connector. – Coax, VHF 3000 megahz (scope probe, cable TV) attenuation, reflectance, Cable TV, Rf • http: //www. netspec. com/helpdesk/wiredoc. html – DC to 4 gigahz Fiber Optics EDGE™

Harness -Twisted Pair What is does: Cancels out crosstalk from neighboring wires and electromagnetic interference from external sources EDGE™

CMOS characteristics Print out the specification sheets. • 1 u. A input? Not sure? Get the spec sheet!. . . • Draw the equivalent circuit for each internal pin. That is, CMOS versus TTL input impedance, output is pull-up or pull-down circuit, current limiting resistor value. • CMOS inputs have very high input impedance which is good for low power consumption for well protected electronics but susceptible to misuse when connecting to the outside world. EDGE™

Isolating Noise • Analog and Digital Optocoupler /Optoisolators Somewhat expensive ($1/ channel) but good isolation. – an electronic device that uses optics to transfer a signal while keeping the receiving and transmitting circuits electrically isolated • http: //www. analog. com (Analog Devices) • http: //www. optoinc. com/optocouplers 1. html • Power connection. • What does not work? – Fuses tipically are ineffective since a fuse is too slow to stop ESD current but good for harness shortcircuit. • Shielding • Fiber Optics – When higher speed data is needed. EDGE™

Isolators • Analog Devices, Isolators http: //www. analog. com/en/sub. Cat/0, 2879, 767%255 F 827%255 F 0%255 F, 00. html • Isolators: http: //www. analog. com/en/prod/0, 2877, ADu. M 2401, 00. html EDGE™

components and spec sheets http: //www. electronicstalk. com/guides/short-circuitprotection. html http: //www. maximic. com/appnotes. cfm/appnote_number/38 http: //www. onsemi. com/Power. Solutions/taxonomy. do? id=29 8 EMI RFI http: //www. edn. com/article/CA 326921. html http: //www. bussmann. com/library/techspec/Tech. Spec 19_su p. pdf#search=%22 short%20 circuit%20 protection%22 http: //www. elecdesign. com/Articles/Index. cfm? AD=1&Artic le. ID=5195 UL 489 and UL 1077 standards EDGE™