GENERAL DESCRIPTION

The ADM3483/ADM3485/ADM3488/ADM3490/ADM3491 are low power, differential line transceivers designed to operate using a single 3.3 V power supply. Low power consumption, coupled with a shutdown mode, makes the ADM3483/ADM3485/ADM3488/ ADM3490/ADM3491 ideal for power-sensitive applications.

The ADM3483/ADM3485 are designed for half-duplex communication.  The ADM3485/ADM3490/ADM3491 transmit at up to 10 Mbps. The receiver input impedance is 12 kΩ, allowing up to 32 trans ceivers to be connected on the bus. A thermal shutdown circuit prevents excessive power dissipation caused by bus contention or by output shorting. If a significant temperature increase is detectedin the internal driver circuitry during fault conditions, then the thermal shutdown circuit forces the driver output into a high impedance state. If the inputs are unconnected (floating), the receiver contains a fail-safe feature that results in a logic high output state. The parts are fully specified over the commercial and industrial temperature ranges. The ADM3483/ADM3485/ ADM3488/ADM3490 are available in 8-lead SOIC_N; the ADM3491 is available in a 14-lead SOIC_N.

 

FEATURES

Operate with 3.3 V supply Interoperable with 5 V logic EIA RS-422 and RS-485 compliant over full common-mode range Data rate options ADM3485/ADM3490/ADM3491: 10 Mbps Half- and full-duplex options Reduced slew rates for low EMI (ADM3483 and ADM3488) 2 nA supply current in shutdown mode (ADM3483/ADM3485/ADM3491) Up to 32 transceivers on the bus −7 V to +12 V bus common-mode range Specified over the –40°C to +85°C temperature range 8 ns skew (ADM3485/ADM3490/ADM3491) 8-lead SOIC and 14-lead SOIC (ADM3491 only) packages

 

APPLICATIONS

Low power RS-485/RS-422 applications Telecom Industrial process control HVAC

 

CIRCUIT DESCRIPTION

The ADM3483/ADM3485/ADM3488/ADM3490/ADM3491 are low power transceivers for RS-485 and RS-422 communications. The ADM3483/ADM3488 transmit and receive at data rates up to 250 kbps; the ADM3485/ADM3490/ADM3491 transmit at up to 10 Mbps. The ADM3488/ADM3490/ADM3491 are full-duplex transceivers, while the ADM3483/ADM3485 are half-duplex REDUCED EMI AND

 

LOW POWER SHUTDOWN MODE (ADM3483/ADM3485/ADM3491)

A low power shutdown mode is initiated by bringing RE high and DE low. The devices do not shut down unless both the driver and receiver are disabled (high impedance). In shutdown mode, the devices typically draw only 2 nA of supply current. For these devices, the tPSH and tPSL enable times assume the part is in the low power shutdown mode; the tPZH and tPZL enable times assume the receiver or driver was disabled, but the part is not shut down.

 

DRIVER OUTPUT PROTECTION

Two methods are implemented to prevent excessive output current and power dissipation caused by faults or by bus contention. Current limit protection on the output stage provides immediate protection against short circuits over the whole common-mode voltage range (see the Typical Performance Characteristics section). In addition, a thermal shutdown circuit forces the driver outputs into a high impedance state if the die temperature rises excessively.

 

PROPAGATION DELAY

Skew time is the difference between the low-to-high and high to-low propagation delays. Small driver/receiver skew times help maintain a symmetrical mark-space ratio (50% duty cycle). The driver skew times are 8 ns for ADM3485/ADM3490/ADM3491.

 

TYPICAL APPLICATIONS

The ADM3483/ADM3485/ADM3491 transceivers are designed for half-duplex bidirectional data communications on multipoint bus transmission lines, Figure 32 and Figure 33 show typical network applications circuits. The ADM3488 and the ADM3490 full-duplex transceivers are designed to be used in a daisy-chain network topology or in a point-to-point application, see Figure 34 and Figure 35. The ADM3491 can be used as line repeat Figure 36. To minimize reflections, the line must be terminated at both ends in its characteristic impedance, and stub lengths off the main line must be kept as short as possible. The slew rate limited ADM3483/ADM3488 are more tolerant of imperfect termination.