User Manual

30 DS671F2
CS4385
4.11 The MUTEC Outputs
The MUTEC1 and MUTEC234 pins have an auto-polarity detect feature. The MUTEC output pins are high
impedance at the time of reset. The external mute circuitry needs to be self-biased into an active state in
order to be muted during re set. Upon release of rese t, the CS4385 will detect the status of the MUTEC pins
(high or low) and will then select that state as the polarity to drive when the mutes become active. The ex-
ternal-bias voltage level that the MUTEC pins see at t he time of releas e of reset must me et the “MUTEC
auto-detect input high/low voltage” specifications as outlined in the Digital Characteri stics section.
Figure 25 shows a single example of both an active high and an active low m ute drive c ircuit. In thes e de-
signs, the pull-up and pull-d own resistors have been especially chosen to meet t he input high/low threshold
when used with the MMUN2111 and MMUN2211 internal bias resistances of 10 kΩ. Use of the Mute Control
function is not mandatory, but recommended, for designs requiring the absolute minimum in extraneous
clicks and pops. Also, use of the Mute Control function can enable the system designer to achieve idle chan-
nel noise/signal-to-noise ratios which are only limited by the external mute circuit.
Figure 24. Recommended Output Filter