ElecSuper MAX485ESA

MAX485ESA is a 5V-powered, ±15kV ESD-protected, slew-rate-limited differential transceiver offering full RS-485 compatibility. Each device contains one driver and one receiver, designed for data transmission with an extended common-mode range (-7V to 12V). The slew-rate-limited driver minimizes EMI and reduces reflections caused by improper cable termination.

The MAX485ESA also features enhanced ESD protection. All transmitter outputs and receiver inputs withstand ±15kV via IEC61000-4-2 air-gap discharge, ±15kV via the Human Body Model, and ±8kV via IEC61000-4-2 contact discharge.

The driver incorporates short-circuit current limiting. A thermal shutdown circuit places the driver outputs into a high-impedance state to prevent excessive power dissipation. Receiver input failsafe ensures a logic-high output when both inputs are open, shorted, or idle.

Both devices feature power-up/power-down modes with glitch-free driver outputs, allowing hot-plugging of transceivers onto a live data bus. The CMOS design significantly reduces power consumption without sacrificing immunity to overdrive or ESD damage. Typical quiescent current is only 300μA in active mode and 1μA in shutdown mode. The MAX485ESA supports half-duplex communication and is available in SOP8 and DIP8 packages.

The MAX485ESA is a low-power RS-485 transceiver capable of error-free data transmission at up to 2.5Mbps in half-duplex mode. It includes Driver Enable (DE) and Receiver Enable (/RE) pins. When disabled, driver and receiver outputs are high-impedance.

When the receiver inputs are shorted, open, or connected to a terminated transmission line with all drivers disabled, the MAX485ESA guarantees a logic-high receiver output. This is achieved by setting the receiver threshold between -50mV and -200mV. If the differential receiver input voltage (A-B) is greater than or equal to -50mV, RO is logic-high; if A-B is less than or equal to -200mV, RO is logic-low. On a terminated bus with all transmitters disabled, the differential input voltage is pulled to 0V by the termination resistor. Due to the MAX485ESA's receiver threshold, this results in a logic-high output with a minimum noise margin of 50mV. Unlike previous failsafe devices, the -50mV to -200mV threshold complies with the ±200mV EIA/TIA-485 standard.

As with all ElecSuper devices, ESD protection structures are integrated on all pins to guard against electrostatic discharge encountered during handling and assembly. The MAX485ESA driver outputs and receiver inputs feature additional ESD protection. ElecSuper engineers have developed advanced structures that protect these pins from ±15kV ESD damage without degradation. ESD-protected pins are tested relative to ground in the powered-down state, withstanding ±15kV under Human Body Model testing.

Standard RS-485 receiver input impedance is 12kΩ (one unit load), and a standard driver can drive up to 32 unit loads. The ElecSuper series transceivers feature a receiver input impedance of 1/8 unit load (96kΩ), allowing up to 256 transceivers to be connected in parallel on a single communication line. Any combination of these devices and/or other RS-485 transceivers may be connected to the line, provided the total load does not exceed 32 unit loads. The MAX485ESA's slew-rate limiting minimizes EMI and reduces reflections.

• RS-485 I/O pin ESD protection
• 15kV Human Body Model
• 15kV IEC61000-4-2 air-gap discharge
• 8kV IEC61000-4-2 contact discharge
• 5V supply voltage range
• Enhanced slew rate limiting for error-free data transmission
• 1μA low-current shutdown mode
• -7V to +12V common-mode input voltage range
• Supports up to 256 transceivers on bus
• Thermal shutdown
• Current limiting for driver overload protection
• Data rates up to 2.5Mbps

• Telecommunications
• Low-power RS-485 transceivers
• ISDN
• Industrial control LAN
• Transceivers for EMI-sensitive applications
• Packet switching
• Level translators