LTC2852IMS

The LTC2852IMS from Analog Devices is a 3.3V full-duplex RS-485/RS-422 transceiver with driver enable (DE) and receiver enable (RE) pins for flexible bus control. It supports data rates up to 20Mbps with ±15kV HBM ESD protection on bus pins. The guaranteed failsafe receiver output goes high when the bus inputs are open or shorted, preventing undefined data. The 1/8 unit load allows up to 256 nodes on a single bus. The 5µA micropower shutdown mode is achieved by driving DE low and RE high, making it ideal for battery-powered applications. The driver outputs are glitch-free during power-up and power-down, preventing bus corruption in hot-plug systems. The MSOP-10 package (3 x 3mm) saves board space compared to SOIC packages.

The LTC2852IMS converts between 3.3V TTL/CMOS logic levels and RS-485 differential bus signals in full-duplex mode. The driver section takes the DI input and, when DE is high, drives the Y and Z outputs as a differential pair: DI high produces positive VOD (Y>Z), DI low produces negative VOD (Y<Z). When DE is low, both driver outputs are high-impedance. The receiver section continuously monitors the A-B differential voltage when RE is low; when |VA-VB| exceeds 200mV, the RO output reflects the polarity. The failsafe biasing ensures RO is high when VA-VB is between -200mV and +200mV (open or shorted bus). When RE is high, RO is high-impedance. The 5µA shutdown is a delayed micropower mode entered when DE is low and RE is high simultaneously; the device fully exits shutdown in approximately 50µs when either enable changes. The driver outputs are current-limited to ±250mA and protected by thermal shutdown that disables the driver at approximately 160°C junction temperature. The receiver has a 1/8 unit load input impedance, allowing 256 transceivers on one bus.

LTC2852IMS uses the 10-lead MSOP (3x3mm) surface-mount package from Analog Devices: Pin 1 = RO (Receiver Output), Pin 2 = RE (Receiver Enable, active-low), Pin 3 = DE (Driver Enable, active-high), Pin 4 = DI (Driver Input), Pin 5 = GND, Pin 6 = Y (Driver Output, non-inverting), Pin 7 = Z (Driver Output, inverting), Pin 8 = B (Receiver Input, inverting), Pin 9 = A (Receiver Input, non-inverting), Pin 10 = VCC (3.0-3.6V). This is a full-duplex transceiver — driver and receiver operate simultaneously on separate bus pairs (Y/Z for transmit, A/B for receive). For half-duplex, short Y to A and Z to B. The MSOP-10 pinout is compatible with LTC2850/2851/2853 family devices.

• Low-Power Comm: 370µA RX mode and 5µA shutdown extend battery life in portable instrumentation and field devices
• Backplane: Glitch-free power transitions prevent data corruption when cards are hot-plugged into live backplanes
• Level Translation: 3.3V logic interface with ±7V common-mode RS-485 bus provides level isolation
• Multi-Drop: 256-node capability with guaranteed failsafe allows large sensor networks without external bias resistors
• Industrial: ±15kV HBM ESD and current-limited drivers survive harsh industrial environments with electrical noise

LTC2852IMS is a 3.3V 20Mbps RS485/RS422 full-duplex transceiver from ADI in MSOP-10. The LTC2851 provides half-duplex operation in MSOP-8. The LTC2854 adds auto-direction control for simplified bus management. The SN65HVD74DGKR from TI provides 3.3V full-duplex with ±30kV ESD. The ADM3485ARZ from ADI offers 3.3V half-duplex in SOIC-8. The THVD1550 from TI provides 50Mbps in VSSOP-8. For 5V operation, LTC485 provides 250kbps half-duplex in SOIC-8.