General Description

The MAX13487E/MAX13488E +5V, half-duplex, ±15kV ESD-protected RS-485-compatible transceivers feature one driver and one receiver. The MAX13487E/MAX13488E include a hot-swap capability to eliminate false transitions on the bus during power-up or live insertion.

The MAX13487E/MAX13488E feature Maxim’s proprietary AutoDirection control. This architecture makes the devices ideal for applications, such as isolated RS-485 ports, where the driver input is used in conjunction with the driver-enable signal to drive the differential bus.

The MAX13487E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free transmission up to 500kbps. The MAX13488E driver slew rate is not limited, allowing transmit speeds up to 16Mbps.

The MAX13487E/MAX13488E feature a 1/4-unit load receiver input impedance, allowing up to 128 transceivers on the bus. These devices are intended for half-duplex communications. All driver outputs are protected to ±15kV ESD using the Human Body Model. The MAX13487E/MAX13488E are available in an 8-pin SO package. The devices operate over the extended -40°C to +85°C temperature range.

 

Applications

Isolated RS-485 Interfaces

Utility Meters

Industrial Controls

Industrial Motor Drives

Automated HVAC Systems

 

Benefits and Features

Robust Protection Increases Reliability

±15kV Human Body Model (HBM) per JEDEC  JS-001-2014

Hot-Swap Capability Eliminates False Transitions on Bus During Power-Up or Live Insertion

AutoDirection Feature Saves PCB Space and BOM Cost by Eliminating One Isolator

Data Rate Options Cover Multiple Applications

500Kbps (MAX13487E) Has Enhanced Slew-Rate Limiting Facilitates Error-Free Data Transmission

16Mbps (MAX13488E) with Max Receiver Propagation Delay of 80ns

Low Shutdown Current of 10μA (max) for Power Savings

Standard 8-Pin SO Package and Pinout for Easy Upgrade of Non-ESD Devices

1/4-Unit Load, Allowing Up to 128 Transceivers on the Bus

 

Detailed Description

The MAX13487E/MAX13488E half-duplex, high-speed transceivers for RS-485/RS-422 communication contain one driver and one receiver. The MAX13487E/MAX13488E feature a hot-swap capability allowing line insertion without erroneous data transfer. The MAX13487E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free transmission up to 500kbps.

 

AutoDirection Circuitry

Internal circuitry in the MAX13487E/MAX13488E, in conjunction with an external pullup resistor on A and pulldown resistor on B, act to automatically disable or enable the driver and receiver to keep the bus in the correct state. This AutoDirection circuitry consists of a state machine and an additional receive comparator that determines whether this device is trying to drive the bus, or another node on the network is driving the bus.

The internal state machine has two inputs:

DI

The current state of A-B (determined by a dedicated differential comparator) The state machine also has two outputs:

DRIVER_ENABLE—Internal signal that enables and disables the driver

RECEIVER_ENABLE—Internal signal that is the inverse of the DRIVER_ENABLE signal, but it can be overridden by an external pin

When DI is low, the device always drives the bus low. When DI is high, the device drives the bus for a short time, then disables the driver and allows the external pullup/pulldown resistors to hold the bus in the high state (A-B > 200mV). During each low-to-high transition of DI, the driver stays enabled until (A-B) > VDT, and then disables the driver, letting the pullup/pulldown resistors hold the A and B lines in the correct state.

 

Idle State

When not transmitting data, the MAX13487E/MAX13488E require the DI input be driven high to remain in the idle state. A conventional RS-485 transceiver has DE and RE inputs that are used to enable and disable the driver and receiver. However, the MAX13487E/MAX13488E does not have a DE input, and instead uses an internal state machine to enable and disable the drivers. DI must be driven high in order to go to the idle state.