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11. NETWORK INTERFACE

Transformer specifications are listed in Table 11-A and Table 11-B. Table 11-C illustrates the series

resistance necessary for the basic interface and is associated with different transformer turns ratios.

Smaller turns ratios result in lower power-supply requirements. However, series resistance provides

added protection from potentially damaging voltages that can occur during lightning strikes. A basic

network interface is illustrated in Figure 11-1. For a complete discussion of network interface design,

refer to Application Note 324: T1/E1 Network Interface Design.

Table 11-A. Specifications for Receive Transformer

SPECIFICATION

RECOMMENDED VALUE

Turns Ratio (all applications)

1:1 ±2%

Primary Inductance

600

mH minimum

Leakage Inductance

1.0

mH maximum

Interwinding Capacitance

40pF maximum

Receive Transformer DC Resistance

Primary (Device Side)

Secondary

1.2Ω maximum

1.2Ω maximum

Table 11-B. Specifications for Transmit Transformer

SPECIFICATION

RECOMMENDED VALUE

Turns Ratio, 5V

1:2 ±2%

Primary Inductance

600

mH minimum

Leakage Inductance

1.0

mH maximum

Interwinding Capacitance

40pF maximum

Transmit Transformer DC Resistance

Primary (Device Side)

Secondary

1.0Ω maximum

2.0Ω maximum

Table 11-C. Transformer Turns Ratio vs. Series Resistance

XFMR2

(CR4.1)

XFMR1

(CR4.0)

OPERATING

VOLTAGE

(V)

APPLICATION

N

Rt (Ω)

Long/Short

1:2

0

0

0

5.0

D4

1:2

0

1:1.15

0

Long/Short

1:2

9.1

0

1

5.0

D4

1:2

0

1:2

4:3

Long/Short

1:1.6

0

1:2

4.3

1

0

5.0

D4

1:1.6

0

1:1.15

0

Long/Short

1:2

9.1

1

1

5.0

D4

1:2

0