MS2548

MS2548 is a 5V-powered, half-duplex RS-485 transceiver. The device features automatic direction control for use in isolated RS-485 port applications, where the driver input works in conjunction with the enable signal to control the device state and drive the differential bus. The chip integrates hot-swap protection and over-temperature protection. The receiver input impedance is 1/4 unit load, allowing up to 128 transceivers on the bus. MS2548 has no slew-rate limiting on the driver, supporting a maximum data rate of 20Mbps. MS2548 is a half-duplex RS-485 transceiver with automatic direction control, integrating hot-swap protection and over-temperature protection — it supports hot-swapping without causing bus output transmission errors. The auto-direction control function works with the pull-up and pull-down resistors on the A and B pins to automatically disable the driver and enable the receiver, ensuring the bus remains in the correct state. This auto-direction control eliminates one DE control signal, offering significant advantages in isolated RS-485 interface designs. The bus pins A and B of MS2548 require external pull-up and pull-down resistors for proper operation. When calculating the resistor values, factors such as RS-485 bus termination method, termination matching resistors, and node count must be considered, ensuring that VA − VB exceeds VTH+ in the idle state to meet the standard receiver threshold. When no data is being transmitted, D should be pulled high to reduce power consumption; MS2548 determines the driver state based on the logic levels of D, A, and B. To address the issue of undefined input pin levels during hot-swapping of RS-485 transceivers, MS2548 forcibly pulls up the D and RE pins for a period during power-up, then disconnects the internal pull-up circuit once the supply voltage has stabilized. When SHDN is pulled low, the device enters a low-power shutdown mode, consuming less than 10μA of supply current.

Applications

• Isolated RS-485 interface
• Energy meters
• Industrial motor drives
• Industrial control
• HVAC systems

Key features

• Meets or exceeds TIA/EIA-485A standard requirements
• 4.5V to 5.5V supply voltage
• Operating temperature range: -40°C to 125°C
• Glitch-free power-up/power-down for hot-swap capability
• Integrated auto-direction control — no separate signal required to control receiver and transmitter states
• 1/4 unit load option (up to 128 bus nodes)
• SOP8 package