Description générale

Devices in the MAX3483E family (MAX3483E/MAX3485E/MAX3490E/MAX3491E) are ±15kV ESD-protected, +3.3V, low-power transceivers for RS-485 and RS-422 communications. Each device contains one driver and one receiver. The MAX3485E, MAX3490E, and MAX3491E transmit at up to 12Mbps.

All devices feature enhanced electrostatic discharge (ESD) protection. All transmitter outputs and receiver inputs are protected to ±15kV using IEC 1000-4-2 Air-Gap Discharge, ±8kV using IEC 1000-4-2 Contact Discharge, and ±15kV using the Human Body Model.

Drivers are short-circuit current limited and are protected against excessive power dissipation by thermal shutdown circuitry that places the driver outputs into a high-impedance state. The receiver input has a fail-safe feature that guarantees a logic-high output if both inputs are open circuit.

The MAX3488E, MAX3490E, and MAX3491E feature fullduplex communication, while the MAX3483E, MAX3485E, and MAX3486E are designed for half-duplex communication.

 

Applications

Télécommunications

Réseaux locaux de contrôle industriel

Émetteurs-récepteurs pour les applications sensibles aux interférences électromagnétiques

Integrated Services Digital Networks

Packet Switching

 

Informations sur les applications

The MAX3483E/MAX3485E/MAX3486E/MAX3488E/MAX3490E/MAX3491E are low-power transceivers for RS-485 and RS-422 communications. The MAX3483E and MAX3488E can transmit and receive at data rates up to 250kbps, the MAX3486E at up to 2.5Mbps, and the MAX3485E/MAX3490E/MAX3491E at up to 12Mbps. The MAX3488E/MAX3490E/MAX3491E are full-duplex transceivers, while the MAX3483E/MAX3485E/MAX3486E are half-duplex. Driver Enable (DE) and Receiver Enable (RE) pins are included on the MAX3483E/MAX3485E/MAX3486E/MAX3491E. When disabled, the driver and receiver outputs are high impedance.

 

MOREDescription

Driver Output Protection

Excessive output current and power dissipation caused by faults or by bus contention are prevented by two mechanisms. A foldback current limit on the output stage provides immediate protection against short circuits over the whole common-mode voltage range (see Typical Operating Characteristics). In addition, a thermal shutdown circuit forces the driver outputs into a high-impedance state if the die temperature rises excessively.

Délai de propagation

There are experiments that show the typical propagation delays. Skew time is simply the difference between the low-to-high and high-to-low propagation delay. Small driver/receiver skew times help maintain a symmetrical mark-space ratio (50% duty cycle).

The receiver skew time, |tPRLH – tPRHL|, is under 10ns 20ns for the MAX3483E/MAX3488E). The driver skew times are 8ns for the MAX3485E/MAX3490E/MAX3491E, 12ns for the MAX3486E, and typically under 50ns for the MAX3483E/MAX3488E.

Line Length vs. Data Rate

The RS-485/RS-422 standard covers line lengths up to 4000 feet. For line lengths greater than 4000 feet, for an example of a line repeater.The results show the system differential voltage for parts driving 4000 feet of 26AWG twisted-pair wire at 125kHz into 120Ω loads.For faster data rate transmission, please consult the factory.

IEC 1000-4-2

The IEC 1000-4-2 standard covers ESD testing and performance of finished equipment; it does not specifically refer to integrated circuits. The MAX3483E family of devices helps you design equipment that meets Level 4 (the highest level) of IEC 1000-4-2, without the need for additional ESD-protection components.

The major difference between tests done using the Human Body Model and IEC 1000-4-2 is higher peak current in IEC 1000-4-2, because series resistance is lower in the IEC 1000-4-2 model. Hence, the ESD withstand voltage measured to IEC 1000-4-2 is generally lower than that measured using the Human Body Model. The results shows the IEC 1000-4-2 model, and the results shows the current waveform for the ±8kV IEC 1000-4-2, Level 4 ESD contact-discharge test.

Applications typiques

The MAX3483E/MAX3485E/MAX3486E/MAX3488E/MAX3490E/MAX3491E transceivers are designed for bidirectional data communications on multipoint bus transmission lines. The results show typical network applications circuits. These parts can also be used as line repeaters, with cable lengths longer than 4000 feet.

To minimize reflections, the line should be terminated at both ends in its characteristic impedance, and stub lengths off the main line should be kept as short as possible.