LXT386LE datasheet(28/78 Pages) INTEL

28 / 78 page

LXT386 — QUAD T1/E1/J1 Transceiver

Datasheet

A capacitor, charged via a measure of the driver output current and discharged by a measure of the

maximum allowable current, is used to detect a secondary short failure. Secondary shorted lines

draw excess current, overcharging the cap. When the capacitor charge deviates outside the nominal

charge window, a driver short circuit fail (DFM) is reported in the respective register by setting an

interrupt. During a long string of spaces, a short-induced overcharge eventually bleeds off, clearing

the DFM flag.

Note that unterminated lines of adequate length (

λ/4) may effectively behave as short-circuits as

seen by the driver and therefore trigger the DFM. Under these circumstances, the alarm should be

disabled.

In addition, LXT386 features output driver short-circuit protection. When the output current

exceeds 100 mA, LXT386 limits the driver’s output voltage to avoid damage.

3.5

Line Protection

Figure 7 on page 29 shows recommended line interface circuitry. In the receive side, the 1 k

Ω

series resistors protect the receiver against current surges coupled into the device. Due to the high

receiver impedance (70 k

Ω typical) the resistors do not affect the receiver sensitivity. In the

transmit side, the Schottky diodes D1-D4 protect the output driver.While not mandatory for normal

operation, these protection elements are strongly recommended to improve the design robustness.

LXT386LE Datasheet(PDF) 28 Page - Intel Corporation