ADM3488ARZ datasheet(14/20 Pages) AD

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ADM3483/ADM3485/ADM3488/ADM3490/ADM3491

Rev. B | Page 14 of 20

CIRCUIT DESCRIPTION

The ADM3483/ADM3485/ADM3488/ADM3490/ADM3491

are low power transceivers for RS-485 and RS-422 communi-

cations. The ADM3483/ADM3488 transmit and receive at data

rates up to 250 kbps; the ADM3485/ADM3490/ADM3491 trans-

mit at up to 10 Mbps. The ADM3488/ADM3490/ADM3491 are

full-duplex transceivers, while the ADM3483/ADM3485 are half-

duplex transceivers. Driver enable (DE) and receiver enable (RE)

pins are included on the ADM3483/ADM3485/ADM3491. When

disabled, the driver and receiver outputs are high impedance.

DEVICES WITH RECEIVER/DRIVER ENABLES—

ADM3483/ADM3485/ADM3491

Table 8. Transmitting Truth Table

Transmitting Input

Transmitting Output

Mode

Normal

High-Z3

Normal

High-Z3

Shutdown

1 A and B outputs are Z and Y respectively, for full-duplex part (ADM3491).

2 X = don’t care.

3 High-Z = high impedance.

Table 9. Receiving Truth Table

Receiving Input

Receiving Output

DE1

A – B

Mode

≥ +0.2 V

Normal

≤ −0.2 V

Normal

Inputs Open

Normal

High-Z3

Shutdown

1 DE is a don’t care; X for the full-duplex part (ADM3491).

2 X = don’t care.

3 High-Z = high impedance.

DEVICES WITHOUT RECEIVER/DRIVER ENABLES—

ADM3488/ADM3490

Table 10. Transmitting Truth Table

Transmitting Input

Transmitting Output

Table 11. Receiving Truth Table

Receiving Input

Receiving Output

A – B

≥ +0.2 V

≤ −0.2 V

Inputs open

REDUCED EMI AND REFLECTIONS—

ADM3483/ADM3488

The ADM3483/ADM3488 are slew rate limited transceivers,

minimizing EMI and reducing reflections caused by improp-

erly terminated cables.

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 ther-

mal 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 receiver skew time (|tPRLH − tPRHL|) is under 10 ns (20 ns

for ADM3483/ADM3488). The driver skew times are 8 ns for

ADM3485/ADM3490/ADM3491 and typically under 100 ns for

ADM3483/ADM3488.

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.

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