ADM4853ARZ-REEL7

The ADM4853ARZ-REEL7 from Analog Devices is a 5V slew-rate limited half-duplex RS-485/RS-422 transceiver from the ADM4850-ADM4857 family, supporting data rates up to 10Mbps. As a half-duplex device, the driver and receiver share the same differential bus lines (A and B), with separate enable inputs (DE for driver enable and RE for receiver enable) allowing flexible control of data flow direction. The 1/8 unit load receiver input impedance (96kOhm) allows up to 256 transceivers to share a single RS-485 bus without exceeding the standard 32 unit-load limit, enabling larger network installations. The slew-rate limited driver outputs reduce electromagnetic interference (EMI) and minimize data errors caused by reflections from improperly terminated transmission lines, making the device well-suited for EMI-sensitive applications. The true fail-safe receiver feature ensures a logic high output when the receiver inputs are open or shorted, guaranteeing a known output state before and after communication. In shutdown mode, the supply current drops to 5uA maximum, making the ADM4853 suitable for battery-powered or low-power standby applications. Thermal shutdown and short-circuit protection prevent excessive power dissipation during fault conditions such as bus contention or output shorting. The device is pin-compatible with the MAX308x family, enabling easy drop-in replacement in existing designs. The ADM4853ARZ-REEL7 is supplied in an 8-lead narrow-body SOIC package on tape and reel.

The ADM4853ARZ-REEL7 operates as a differential RS-485/RS-422 half-duplex transceiver. Key subsystems include: (1) Driver Section – when DE is high, the driver is enabled and converts the single-ended DI (driver input) signal into a differential output on the A and B bus lines; the driver output is slew-rate limited to reduce high-frequency EMI emissions and minimize reflections on improperly terminated buses; the differential output voltage is guaranteed to be at least 1.5V across a 27-ohm load (RS-485) or 2.0V across a 54-ohm load (RS-422); when DE is low, the driver outputs are three-stated (high impedance) to avoid loading the bus; (2) Receiver Section – when RE is low, the receiver is enabled and compares the differential voltage (VA – VB) against a threshold; if VA – VB > 200mV, the RO (receiver output) is logic high; if VA – VB < -200mV, RO is logic low; the true fail-safe feature ensures RO = high when inputs are open (no connection) or shorted (A = B), preventing undefined receiver states; when RE is high, the receiver output is three-stated; (3) Half-Duplex Operation – the driver and receiver share the same A/B bus pins; for transmission, DE is driven high and RE can be high or low (receiver output ignored); for reception, DE is driven low (driver three-stated) and RE is driven low; direction control is typically managed by tying DE and RE together or using a GPIO pin; (4) 1/8 Unit Load – the high receiver input impedance (96kOhm vs 12kOhm for a full unit load) reduces the loading on the bus, allowing 256 devices instead of the standard 32; (5) Protection – thermal shutdown disables the driver when junction temperature exceeds approximately 150C; short-circuit current is limited to approximately 200mA; the bus pins tolerate common-mode voltages from -7V to +12V.

• Industrial Modbus network: 256 nodes on single twisted-pair bus at 10Mbps with fail-safe idle state
• Building automation BACnet: slew-rate limited driver reduces EMI in long cable runs (up to 1200m at lower data rates)
• Battery-powered data logger: 5uA shutdown current preserves battery during idle periods between readings
• DTE-DCE interface: half-duplex RS-485 link between PLC and remote I/O module with direction auto-control
• Level translation: RS-485 bus extends UART communication between 3.3V/5V systems over long distances