HGSEMI ADM485EARZ/HG

The ADM485E is a +5.0V powered RS-485/RS-422 transceiver with ±16kV ESD protection. It features a failsafe circuit that drives the receiver output to a logic high when the receiver inputs are open or shorted, or when all transmitters connected to a terminated bus are disabled. The full product family supports hot plug capability, eliminating glitches on the bus during power-up or hot insertion.

The ADM485E driver provides an exceptionally large output voltage swing (exceeding 2.1V into a 54Ω load), ensuring higher noise margin. The ADM485E driver has an unlimited slew rate, enabling data rates up to 10Mbps.

The ADM485E is designed for half-duplex communication. All devices feature 1/8 unit load receiver input impedance, allowing up to 256 transceivers on the bus.

The ADM485E is available in an 8-lead SOP package, and the devices are offered in the industrial temperature range.

The ADM485 family of high-speed RS-485/RS-422 transceivers integrates one driver and one receiver. These devices incorporate a failsafe circuit (refer to the Failsafe section) and support hot plug capability for hot insertion without data transmission errors (refer to the Hot Plug Feature section). The ADM485E driver has an unlimited slew rate, enabling data rates up to 10Mbps. All devices operate from a single +5.0V supply. The driver features output short-circuit current limiting. A thermal shutdown circuit protects the driver from excessive power dissipation; upon entering thermal shutdown, the driver outputs are placed in a high-impedance state.

When a board is inserted into a live or active backplane (hot plug input), differential disturbances on the data bus may cause data errors. Upon insertion, the data communication processor initiates a power-up sequence during which the processor's logic output drivers are in a high-impedance state and cannot drive the DE and RE inputs of these devices to the specified logic levels. Logic drivers in the high-impedance state may exhibit leakage currents up to ±10μA, causing the transceiver's standard CMOS enable inputs to drift to incorrect logic levels. Additionally, board parasitic capacitance can couple VCC or GND to the enable inputs. Without hot plug capability, these factors can inadvertently enable the transceiver driver or receiver. The ADM485 hot plug feature ensures that during VCC ramp-up, internal circuitry holds DE low and RE high. Once the initial power-up sequence is complete, the pull-down circuitry is deactivated and the hot plug inputs are reset.

All pins incorporate ESD protection structures to guard the device against electrostatic discharge during operation and assembly. The ADM485 family provides additional ESD protection on the driver outputs and receiver inputs. Dedicated circuit structures have been developed to protect these pins, enabling them to withstand ±16kV ESD strikes per the IEC 61000-4-2 model. The ESD protection structures can withstand high-level ESD strikes under all conditions, including normal operating mode, shutdown mode, and power-off mode. ESD protection can be verified using different test methods. The ADM485 transmitter outputs and receiver inputs have been tested for protection under the following conditions:

±16kV, HBM (Human Body Model).

±16kV, Air Discharge method per IEC 61000-4-2.

±16kV, Contact Discharge method per IEC 61000-4-2.

• True fail-safe receiver, low-power shutdown mode
• DE and RE with hot-swap input structure
• +5.0V supply voltage, up to 256 transceivers on the bus
• I/O pins with enhanced ESD protection (±16kV IEC 61000-4-2 model)

RS-422/RS-485 Communications

• Digital electric/water meters, industrial control
• Industrial embedded computers and peripherals, security surveillance systems
• Routers and switches, instrumentation, level shifting
• EMI-sensitive transceiver applications