Conventional ESD countermeasures

External clamping devices such as ESD suppressors (TVS diodes) are typically used to protect silicon devices such as RS-485 transceivers from voltage transients.
ESD protection is achieved by clamping voltage spikes to a certain limit with the low impedance of a PN junction avalanche breakdown.

When a TVS diode experiences a transient voltage and the surge voltage becomes greater than the TVS breakdown voltage, the resistance of the TVS decreases to maintain a constant clamp voltage. Transient voltages are clamped instantaneously (<1ns), preventing damaging currents from flowing to the protected device.
A TVS diode can be modeled with a large resistance and capacitance in parallel when operating below its breakdown voltage.

In this way, external components such as ESD suppressors have been used for ESD countermeasures.

RS-485 device with enhanced ESD protection - ADM3065E -

Analog Devices, Inc. offers a wide range of RS-485 devices that provide enhanced ESD protection without the need for external components such as ESD suppressors.

The letter E after the part number, such as ADM3072E, indicates enhanced ESD protection.

The ADM3065E, a new RS-485 transceiver that withstands IEC electrostatic discharge (ESD) from 3.0 V to 5.5 V, can withstand ±12 kV of contact discharge on the transceiver bus pins without latch-up or damage. Can withstand.

Features of the ADM3065E

• Compliant with TIA/EIA RS-485 over full supply voltage range
• VCC operating voltage range: 3.0 V to 5.5 V
• ESD protection for bus pins
  • IEC 61000-4-2 ≥ ±12 kV contact discharge
  • IEC61000-4-2 ≥ ±12 kV air discharge
  • HBM ≥ ±30 kV

   

• Hot swap support (glitch free power up/power down)
• High speed data rate: 50 Mbps
• Fail-safe against receiver shorts, open circuits, and bus idle
• Wide temperature range up to 125 °C
• Profibus compliant with VCC ≥ 4.5V
• half duplex
• Allows connection of up to 128 nodes on the bus
• Space-saving packaging options
  • 8-pin, 3mm × 3mm MSOP package
  • 8-pin narrow body SOIC_N package

   

Benefits of the ADM3065E

• industrial fieldbus
  • PROFIBUS compliant under all operating conditions when powered below 4.5V
  • Space savings in motor control where PCB area is highly constrained
  • Design flexibility with VCC 3.0 to 5.5V operating voltage range

• building automation
  • Robust communication systems are required in environments with moving cables and close motor and inductor distances.
  • IEC61000-4-2 ESD protection (±12kV contact discharge, ±12kV air discharge)

• process control
  • Hot-swap capability to properly enable drivers and receivers during backplane power input changes
  • 50Mbps data rate to meet high-speed communication demands

Example of using ADM3065E in motor encoder

RS-485 communication between servo drives and encoders typically requires timing specifications of high data rates up to 16MHz and low propagation delays. It can also be exposed to harmful EMC events such as ESD. Furthermore, the PCB area of the encoder is very limited, requiring a compact solution.

The ADM3065E meets these challenges with its high speed, high ESD tolerance, and small package.

Assumed target application

• industrial fieldbus
• process control
• building
• automation
• Profibus network
• motor control servo
• Drive and encoder

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