CS8420-CSR datasheet(79/94 Pages) CIRRUS

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DS245F4

CS8420

The TXP pin may be used to drive TTL or CMOS gates as shown in Figure 32. This circuit may be used for

optical connectors for digital audio since they usually have TTL or CMOS compatible inputs. This circuit is

also useful when driving multiple digital audio outputs since RS422 line drivers have TTL compatible inputs.

14.2

AES3 Receiver External Components

The CS8420 AES3 receiver is designed to accept both the professional and consumer interfaces. The dig-

ital audio specifications for professional use call for a balanced receiver, using XLR connectors, with 110

±20% impedance. The XLR connector on the receiver should have female pins with a male shell. Since the

receiver has a very high input impedance, a 110

Ω resistor should be placed across the receiver terminals

to match the line impedance, as shown in Figure 33. Although transformers are not required by the AES,

they are, however, strongly recommended.

If some isolation is desired without the use of transformers, a 0.01

μF capacitor should be placed in series

with each input pin (RXP and RXN) as shown in Figure 34. However, if a transformer is not used, high

frequency energy could be coupled into the receiver, causing degradation in analog performance.

Figures 33 and 34 show an optional DC blocking capacitor (0.1

μF to 0.47 μF) in series with the cable input.

This improves the robustness of the receiver, preventing the saturation of the transformer, or any DC current

flow, if a DC voltage is present on the cable.

In the configuration of systems, it is important to avoid ground loops and DC current flowing down the shield

of the cable that could result when boxes with different ground potentials are connected. Generally, it is

good practice to ground the shield to the chassis of the transmitting unit, and connect the shield through a

capacitor to chassis ground at the receiver. However, in some cases it is advantageous to have the ground

of two boxes held to the same potential, and the cable shield might be depended upon to make that electrical

TXP

TXN

TTL or

CMOS Gate

CS8420

Figure 32. TTL/CMOS Output Circuit

XLR

Twisted

Pair

110

CS8420

RXP

RXN

*See Text

Figure 33. Professional Input Circuit

XLR

Twisted

Pair

110

CS8420

RXP

RXN

0.01 F

*See Text

Figure 34. Transformerless Professional Input Circuit

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