Datasheet

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R1andR2areselectedtoachievethedesiredoutputvoltagelevelwhilemaintainingtherequired75 transmitteroutputimpedance.W
TheTX+outputimpedanceisnegligible.
(a)Transformer-CoupledUnbalancedOutput
1:1
R2
0.1 Fm
TX+
DigitalOutput
75 UnbalanW ced
(RCAorBNCconnector)
R1
(b)UnbalancedOutputWithoutTransformer
R2
0.1mF
TX+
DigitalOutput
75 UnbalanW ced
(RCAorBNCconnector)
R1
(1)ToshibaTOTX141,TOTX173,TOTX176,TOTX179,orequivalent.
SN74AVC1T45
orEquivalent
IfVIO<+3.0V.
VIO
5
+3.3V
6
3
1
2
4
All-PlasticFiber
(5or10metersmaximum)
AESOUT
Optical
Transmitter
(1)
DIX4192
SBFS031C – JANUARY 2006 – REVISED JUNE 2006
APPLICATIONS INFORMATION (continued)
Figure 31. 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 DIX4192, 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 configuration will boost the logic high level to a voltage suitable for driving the
TTL-compatible input configuration. Figure 32 shows the recommended optical transmitter interface circuits.
Figure 32. Interfacing to an Optical Transmitter Module
The AESOUT output may also be used to drive external logic or line driver devices directly. Figure 33 illustrates
the recommended logic interface techniques, including connections with and without level translation. Figure 34
illustrates an external line driver interface utilizing the Texas Instruments SN75ALS191 dual differential line
driver. If the VIO supply of the DIX4192 is set from +3.0V to +3.3V, no logic level translation will be 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 34 will be required. The SN75ALS191 dual line driver is especially
useful in applications where simultaneous 75 Ω and 110 Ω line interfaces are required.
31
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