Tudi ADM1485ARMZ-TUDI

The ADM1485 is a differential line transceiver designed for high-speed bidirectional data communication on multipoint bus transmission lines. It is designed for balanced data transmission and complies with RS-485 and RS-422 EIA standards. The device contains a differential line driver and a differential line receiver. Both the driver and receiver can be independently enabled. When disabled, the outputs are three-stated.

The ADM1485 is powered from a single 5V supply. Excessive power dissipation caused by bus contention or output short circuits is prevented by a thermal shutdown circuit. Under fault conditions, when a significant temperature increase is detected in the internal driver circuit, this feature forces the driver outputs into a high-impedance state.

Up to 32 transceivers can be connected to the bus simultaneously, but only one driver should be enabled at any time. It is therefore important that the remaining disabled drivers do not load the bus. To ensure this, the ADM1485 driver maintains high output impedance when both disabled and powered down.

This minimizes the load impact of transceivers when not in use. The high-impedance driver outputs remain unchanged throughout the common-mode voltage range from −7V to +12V. The receiver includes a failsafe feature that causes a logic-high output state if the input is unconnected (floating).

The ADM1485 is fabricated using a BiCMOS process, an advanced mixed-technology process combining low-power CMOS and fast-switching bipolar technologies. All inputs and outputs incorporate ESD protection; all driver outputs feature high source and sink current capability. An epitaxial layer is used to prevent latch-up.

The ADM1485 is a 5V, half-duplex, low-power, slew-rate-limited RS-485 transceiver that fully meets TIA/EIA-485 standard requirements. The ADM1485 integrates one driver and one receiver, both of which can be independently enabled and disabled. When both are disabled, both the driver and receiver outputs enter a high-impedance state. The ADM1485 features 1/8 unit load, allowing up to 160 transceivers to be connected in parallel on the same bus. The slew-rate-limited driver significantly reduces EMI and reflections caused by improperly terminated cables, enabling error-free data transmission at rates up to 500 kbps–40 Mb transient. The ADM1485 operates over a supply voltage range of 4.75 V to 5.25 V and provides failsafe protection, over-temperature protection, current-limiting protection, overvoltage protection, and hot-swap capability on control pins. The ADM1485 offers excellent ESD performance: HBM ±15 kV, contact discharge per IEC 61000-4-2 ±15 kV.

The ADM1485 is a half-duplex, high-speed RS-485/RS-422 transceiver incorporating one driver and one receiver. It features failsafe protection, overvoltage protection, overcurrent protection, over-temperature protection, and hot-swap inputs on the /RE and DE pins.

The ADM1485 slew-rate-limited driver reduces EMI and reflections caused by improperly terminated cables, enabling error-free data transmission at up to 500 kbps.

When the receiver inputs are shorted or open, or when all drivers connected to a terminated transmission line are disabled (idle), the ADM1485 guarantees a logic-high output at the receiver. This is achieved by setting the receiver input thresholds to −50 mV and −200 mV respectively. If the differential receiver input voltage (A−B) ≥ −50 mV, RO is logic high; if (A−B) ≤ −200 mV, RO is logic low. When all transmitters on a terminated bus are disabled, the differential input voltage at the receiver is pulled to 0V through the termination resistor. Based on the receiver threshold, a logic-high level with a minimum noise margin of 50 mV is achieved. The −50 mV to −200 mV threshold window is compliant with the ±200 mV EIA/TIA-485 standard.

The standard RS-485 receiver input impedance is 12 kΩ (1 unit load), and a standard driver can drive up to 32 unit loads. The ADM1485 receiver has a 1/8 unit load input impedance (96 kΩ), allowing up to 160 transceivers to be connected in parallel on the same bus. These devices may be used in any combination, or mixed with other RS-485 transceivers, as long as the total load does not exceed 32 unit loads on the same bus.

The ADM1485 slew-rate-limited driver reduces EMI and reflections caused by improperly terminated cables; the driver rise time is related to the length of the termination.

Two mechanisms prevent excessive output current and power dissipation due to faults or bus contention. First, current-limiting protection provides fast short-circuit protection across the full common-mode voltage range (refer to typical operating characteristics). Second, a thermal shutdown circuit forces the driver outputs into a high-impedance state when the die temperature exceeds 150°C.

The ADM1485 RS-485 transceiver is designed for bidirectional data communication on multipoint bus transmission lines. These devices can also be used as line repeaters for cable lengths exceeding 4000 feet. To reduce reflections, the transmission line should be terminated at both ends with its characteristic impedance, and stub lengths beyond the main trunk should be kept as short as possible.

• Compliant with EIA RS-485 standard
• Single 5V supply
• -7V to -12V bus common-mode range
• High-speed, low-power BiCMOS
• Thermal shutdown protection
• Short-circuit protection
• Advanced upgrade of LTC1485
• 1/8 unit load, allowing up to 160 devices on the bus
• Driver short-circuit output protection
• Over-temperature protection
• Low-power shutdown
• /RE, DE pins allow hot-swap inputs
• Receiver open-circuit failsafe
• Strong noise immunity
• Integrated transient voltage suppression
• A, B port protection: contact discharge ±15KV, HBM ±15KV

• Low-power RS-485 systems
• DTE-DCE interfaces
• Packet switching
• LAN data
• Concentrator data
• Multiplexers
• Integrated Services Digital Network (ISDN)