±15kV ESD-Protected, 32Mbps, 3V/5V,

Triple RS-422/RS-485 Receivers with Fault Detection

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11

Common-Mode Range

The MAX3097E/MAX3098E contain circuitry that de-

tects if the input stage is going outside its useful com-

mon-mode range. If the received data could be

unreliable, a fault signal is triggered.

Detecting Low Input Differential

Due to cable attenuation on long wire runs, it is possi-

received. In this condition, a fault will be indicated.

Delayed Fault Output

The delayed fault output provides a programmable

blanking delay to allow transient faults to occur without

triggering an alarm. Such faults may occur with slow

signals triggering the receiver alarm through the zero

crossover region.

Figure 9 shows the delayed alarm output.

ALARMD performs a logic OR of ALARMA, ALARMB,

and ALARMZ (Figure 10). A NOR gate drives an N-

channel MOSFET so that in normal operation with no

faults, the current source (10µA typ) is shunted to

ground. Upon activation of any alarm from receiver A,

B, or Z, the MOSFET is turned off, allowing the current

DELAY threshold, the comparator output, ALARMD,

goes high. ALARMD is reset when all receiver alarms

Setting Delay Time

ALARMD’s delay time is set with a single capacitor

connected from DELAY to GND. The delay comparator

value can be determined for a given time delay period

from the Capacitance vs. ALARMD Output Delay graph

in the Typical Operating Characteristics or using the

following equations:

and

ALARMA

ALARMB

ALARMD

ALARMA

ALARMB

ALARMZ

ALARMD

DELAY

COMPARATOR

NMOS

DELAY

CURRENT

SOURCE

(EXTERNAL)

G1

DELAY THRESHOLD

ALARM_

DELAY

ALARMD

output will be present at ALARMD.

Figure 9. Delayed Alarm Output

Figure 10. ALARMD Simplified Schematic

Figure 8. Short-Circuit Detection

A

NORMAL OPERATION

SHORT CIRCUIT A TO A

A