Datasheet

Maxim Integrated │ 145
MAX98090 Ultra-Low Power Stereo Audio Codec
www.maximintegrated.com
To prevent audible crosstalk, the switching frequency in
all three charge pump ranges is well outside of the audio
band. In addition, to prevent audible distortion during
supply range changes, the charge pump transitions from
one output power range to another very quickly. When
changing from the half supply range (±V
HPVDD
/2) to
the full supply range (±V
HPVDD
/2), the transition occurs
immediately if the threshold is exceeded (to avoid clipping
for a rapidly increasing audio output). When moving back
down, there is a 32ms delay between the threshold detec-
tion and the supply range transition. The quick supply
level transitions draw a significant transient current from
HPVDD. To prevent a droop/glitch on HPVDD, the bypass
capacitance must be appropriate to supply the required
transient current (Figures 53 and 54).
Click-and-Pop Reduction
The device includes extensive click-and-pop reduction
circuitry designed to minimizes audible clicks and pops
at turn-on, turn-off, and during volume changes. These
features include zero-crossing detection, volume change
smoothing, and volume change stepping (Table 75).
Zero-crossing detection is available on the analog micro-
phone input PGAs and all analog output PGAs and
volume controls to prevent large glitches when volume
changes are made. Instead of making a volume change
immediately, the change is made when the audio signal
crosses the midpoint (Figure 42). If no zero crossing
occurs within the timeout window (100ms), the volume
change occurs regardless of signal level.
Figure 41. Class H Amplifier Supply Range Transitions
Figure 42. Zero-Crossing Detection
V
HPVDD
V
HPVDD
2
GND
V
TH_25%
-V
HPVDD
2
V
CPVDD
V
CPVSS
V
HP_OUT
-V
TH_25%
32ms
32ms
-V
HPVDD
GND
ZERO-CROSSING DETECTION
DISABLED (ZDEN = 1)
I
2
C PGA
VOLUME
CHANGE
I
2
C PGA
VOLUME
CHANGE
AUDIO
OUTPUT
VOLUME
CHANGE
AUDIO
OUTPUT
VOLUME
CHANGE
GND
ZERO-CROSSING DETECTION
ENABLED (ZDEN = 0)