Rainbow Electronics MAX5559 - Manual (Page 16)

MAX5556–MAX5559
Low-Cost Stereo Audio DACs
16 _______________________________________________________________________________________
Pop and Click Suppression
The MAX5556–MAX5559 feature a pop and click
supression routine to reduce the unwanted audible
effects of system transients. This routine produces
glitch-free operation at the outputs during power-on,
loss of clock, or invalid clock conditions. See Figure 13
for a detailed state diagram during transient conditions.
Power-Up
Once the MAX5556–MAX5559 recognize a valid
MCLK/LRCLK ratio (256, 384, or 512), the analog outputs
(OUTR and OUTL) are enabled in stages using a glitch-
less ramping routine. First, the outputs ramp up to the
quiescent output voltage at a rate of 5V/s typ (see Figure
14). After the outputs reach the quiescent voltage, the
converted data stream begins soft-start ramping, achiev-
ing the full-scale operation over a 20ms period.
If invalid clock signals are detected while the outputs
are DC ramping to their quiescent state, the outputs
stop ramping and hold their preset values until valid
clock signals are restored (Figure 15).
Loss of Clock and Invalid Clock Conditions
The MAX5556–MAX5559 mute both outputs after
detecting one of four invalid clock conditions. All four
devices mute their outputs to prevent propagation of
pops, clicks, or corrupted data through the signal path.
The MAX5556–MAX5559 force the outputs to the quies-
cent DC voltage (2.4V) to prevent clicks in capacitive-
coupled systems. Invalid clock conditions include:
1. MCLK/LRCLK ratio changes between 256, 384,
and 512
2. Transition between internal and external serial-
clock mode
3. Invalid MCLK/LRCLK ratio
4. MCLK falls below the minimum operating
frequency 2kHz
When the MCLK/LRCLK ratio returns to 256, 384, or
512 and MCLK is equal or greater than its minimum
operating frequency, the MAX5556–MAX5559 outputs
return to their full-scale setting over a soft-start mute
time of 20ms (Figure 15).
Power-Down
When the positive supply is removed from the
MAX5556–MAX5559, the outputs discharge to ground.
When power is restored, the power-up ramp routine
engages once a valid clock ratio is established (see the
Power-Up section).
Avoid violating absolute maximum conditions by sup-
plying digital inputs to the part or forcing voltages on
the analog outputs during a loss-of-power event.
Applications Information
Low-Cost Line-Level Solution
Connect the MAX5556–MAX5559 outputs through a
passive output filter as detailed in Figure 11 for a
low-cost solution. This lowpass filter yields single-pole
(20dB/decade) roll-off at a corner frequency (f
C )
determined by:
In the case of Figure 11, f C is approximately 190kHz.
High-Performance Line-Level Solution
For enhanced performance, connect the MAX5556–
MAX5559 outputs to an active filter by using an opera-
tional amplifier as shown in Figure 12. The use of an
active filter allows for steeper roll-off, more efficient fil-
tering, and also adds the capability of a programmable
output gain.
Power-Supply Sequencing
For correct power-up sequencing, apply V DD and then
connect the input digital signals. Do not apply digital sig-
nals before V
DD is applied.
Do not violate any of the absolute maximum ratings by
removing power with the digital inputs still connected.
To correctly power down the device, first disconnect
the digital input signals, and then remove V
DD .
f
RC
C
=
1
2π