Cirrus Logic CS4385A - Manual (Page 30)

30 DS837F2
CS4385A
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 reset. Upon release of reset, the CS4385A will detect the status of the MUTEC
pins (high or low) and 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 the time of release of reset must meet the “MUTEC
auto-detect input high/low voltage” specifications as outlined in the Digital Characteristics section.
Figure 24 shows a single example of both an active high and active low mute drive circuit. In these designs,
the pull-up and pull-down resistors have been especially chosen to meet the input high/low threshold when
used with the MMUN2111 and MMUN2211 internal bias resistances of 10 k
. Use of the Mute Control func-
tion 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 channel
noise/signal-to-noise ratios that are only limited by the external mute circuit.
4.12 Recommended Power-Up Sequence
4.12.1 Hardware Mode
1. Hold RST low until the power supplies and configuration pins are stable, and the master and left/right
clocks are locked to the appropriate frequencies, as discussed in Section 4.1 . In this state, the
registers are reset to the default settings, FILT+ will remain low, and VQ will be connected to VA/2.
If RST cannot be held low long enough, the SDINx pins should remain static low until all other clocks
are stable, and if possible, the RST should be toggled low again once the system is stable.
2. Bring RST high. The device will remain in a low power state with FILT+ low and will initiate the
Hardware power-up sequence after approximately 512 LRCK cycles in Single-Speed Mode (1024
LRCK cycles in Double-Speed Mode, and 2048 LRCK cycles in Quad-Speed Mode).
Figure 24. Recommended Mute Circuitry