SRC4382IPFBT datasheet(45/85 Pages) TI2

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SN74LVC1G125

orEquivalent

0.1mF

T RX+

ToRX-

From+5VLogic

(TTLorCMOS)

VDD33

SN74AVC1T45

orEquivalent

0.1mF

T RX+

ToRX-

From+1.8Vor+2.5V

CMOSLogic

+1.8Vor+2.5V

VDD33

TRANSMITTER OUTPUT INTERFACING

1:1

0.1 F

TX+

TX-

XLR

DigitalOutput

110

alanced

110W

SRC4382

SBFS030C – JANUARY 2006 – REVISED SEPTEMBER 2007

The SRC4382 line receivers may also be driven directly from external logic or line receiver devices with TTL or

CMOS outputs. If the logic driving the line receiver is operated from +3.3V, then logic level translation is not be

required. However, if the external logic is operated from a power-supply voltage that exceeds the maximum

VDD33 supply voltage of the SRC4382, or operates from a supply voltage lower than +3.3V, then level

translation is required. Figure 87 shows the recommended logic level translation methods, utilizing buffers and

level translators available from Texas Instruments.

Figure 87. CMOS/TTL Input Logic Interface

This section details the recommended interfaces for the SRC4382 transmitter line driver and CMOS buffered

outputs. Balanced and unbalanced line interfaces, in addition to optical transmitter and external logic interfacing,

will be discussed.

For professional digital audio interfaces, 110

Ω balanced line interfaces are either required or preferred.

Transformer coupling is commonly employed to provide isolation and to improve common-mode noise

performance. Figure 88 shows the recommended transformer-coupled balanced line driver interface for the

SRC4382. The transformer is specified for a 1:1 turn ratio, and should exhibit low inter-winding capacitance for

best performance. To eliminate residual DC bias, a 0.1

μF capacitor is utilized for AC-coupling the transformer to

the line driver outputs. The coupling capacitor should be a surface-mount ceramic chip type with an X7R or C0G

dielectric.

Figure 88. Transformer-Coupled Balanced Output Interface

Unbalanced 75

Ω coaxial cable interfaces are commonly employed in consumer and broadcast audio

applications. Designs with and without transformer line coupling may be utilized. Figure 89(a) illustrates the

recommended 75

Ω transformer-coupled line driver interface, which shares many similarities to the balanced

design shown in Figure 88. Figure 89(b) illustrates the transformer-free line driver interface, which is commonly

used for S/PDIF consumer connections.

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