SRC4392IPFBT datasheet(46/95 Pages) TI2

46 / 95 page

(1)ToshibaTOTX141,TOTX173,TOTX176,TOTX179,orequivalent.

SN74AVC1T45

orEquivalent

IfVIO<+3.0V.

VIO

+3.3V

All-PlasticFiber

(5or10metersmaximum)

AESOUT

Optical

Transmitter

(1)

R1andR2areselectedtoachievethedesiredoutputvoltagelevelwhilemaintainingtherequired75

transmitteroutputimpedance.

TheTX+outputimpedanceisnegligible.

(a)Transformer-CoupledUnbalancedOutput

1:1

0.1 F

TX+

DigitalOutput

Unbalan

ced

(RCAorBNCconnector)

(b)UnbalancedOutputWithoutTransformer

0.1mF

TX+

DigitalOutput

Unbalan

ced

(RCAorBNCconnector)

SRC4392

SBFS029D – DECEMBER 2005 – REVISED DECEMBER 2012

www.ti.com

Figure 89. Unbalanced Line Output Interfaces

Optical interfaces utilizing all-plastic fiber are commonly employed for consumer audio equipment where

interconnections are less than 10m in length. Most optical transmitter modules utilized for a digital audio interface

operate from a single +3.3V or +5V supply and have a TTL compatible logic input. The CMOS buffered

transmitter output of the SRC4392, AESOUT (pin 34), is capable of driving the optical transmitter with VIO supply

voltages down to +3.0V. If the VIO supply voltage is less than +3.0V, then level translation logic is required to

drive the optical transmitter input. A good choice for this application is the Texas Instruments SN74AVC1T45

single bus transceiver. This device features two power-supply rails, one for the input side and one for the output

side. For this application, the input side supply is powered from the VIO supply, while the output side is powered

from a +3.3V supply. This will boost the logic high level to a voltage suitable for driving the TTL compatible input

configuration. Figure 90 shows the recommended optical transmitter interface circuits.

Figure 90. Interfacing to an Optical Transmitter Module

The AESOUT output may also be used to drive external logic or line driver devices directly. Figure 91 illustrates

the recommended logic interface techniques, including connections with and without level translation. Figure 92

illustrates an external line driver interface utilizing the Texas Instruments SN75ALS191 dual differential line

driver. If the VIO supply of the SRC4392 is set from +3.0V to +3.3V, no logic level translation is required between

the AESOUT output and the line driver input. If the VIO supply voltage is below this range, then the optional logic

level translation logic of Figure 92 is required. The SN75ALS191 dual line driver is especially useful in

applications where simultaneous 75

Ω and 110Ω line interfaces are required.

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