DS2153Q datasheet(36/52 Pages) DALLAS

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DS2153Q

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TRANSFORMER SPECIFICATIONS Table 12-3

SPECIFICATION

RECOMMENDED VALUE

Turns Ratio

1:1 (receive) and 1:1.15 or 1:1.36 (transmit)

±5%

Primary Inductance

600

µH minimum

Leakage Inductance

1.0

µH maximum

Interwinding Capacitance

60 pF maximum

DC Resistance

1.2 ohms maximum

12.3 Jitter Attenuator

The DS2153Q contains an onboard jitter attenuator that can be set to a depth of either 32 or 128 bits via

the JABDS bit in the Line Interface Control Register (LICR). The 128-bit mode is used in applications

where large excursions of wander are expected. The 32-bit mode is used in delay-sensitive applications.

The characteristics of the attenuation are shown in Figure 12.4. The jitter attenuator can be placed in

either the receive path or the transmit path by appropriately setting or clearing the JAS bit in the LICR.

Also, the jitter attenuator can be disabled (in effect, removed) by setting the DJA bit in the LICR. In order

for the jitter attenuator to operate properly, a crystal with the specifications listed in Table 12.4 below

must be connected to the XTAL1 and XTAL2 pins.

The jitter attenuator divides the clock provided by the 8.192 MHz crystal at the XTAL1 and XTAL2 pins

to create an output clock that contains very little jitter.

Onboard circuitry will pull the crystal (by

switching in or out load capacitance) to keep it long-term averaged to the same frequency as the incoming

E1 signal. If the incoming jitter exceeds either 120 UIpp (buffer depth is 128 bits) or 28 UIpp (buffer

depth is 32 bits), then the DS2153Q will divide the attached crystal by either 3.5 or 4.5 instead of the

normal 4 to keep the buffer from overflowing. When the device divides by either 3.5 or 4.5, it also sets

the Jitter Attenuator Limit Trip (JALT) bit in the Receive Information Register (RIR.5).

CRYSTAL SPECIFICATIONS GUIDELINES Table 12-4

PARAMETER

SPECIFICATION

Parallel Resonant Frequency

8.192 MHz

Mode

Fundamental

Load Capacitance

18 pF to 20 pF (18.5 pF nominal)

Tolerance

±50 ppm

Pullability

CL=10 pF, delta frequency=+175 to +250 ppm

CL=45 pF, delta frequency=-175 to -250 ppm

Effective Series Resistance

30 ohms maximum

Crystal Cut

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