Datasheet
MAX98355A/MAX98355B
PCM Input Class D Audio Power Amplifiers
28Maxim Integrated
Maxim’s spread-spectrum modulation mode flattens
wideband spectral components while proprietary tech-
niques ensure that the cycle-to-cycle variation of the
switching period does not degrade audio reproduction or
efficiency. The ICs’ spread-spectrum modulator random-
ly varies the switching frequency by Q10kHz around the
center frequency (300kHz). Above 10MHz, the wideband
spectrum looks like noise for EMI purposes (Figure 14).
Speaker Current Limit
If the output current of the speaker amplifier exceeds the
current limit (2.8A typ), the IC disables the outputs for
approximately 100Fs. At the end of the 100Fs, the out-
puts are re-enabled. If the fault condition still exists, the
IC continues to disable and re-enable the outputs until
the fault condition is removed.
Gain Selection
The ICs offer five programmable gain selections through
a single gain input (GAIN). Gain is referenced to the
full-scale output of the DAC, which is 2.1dBV (Table 7).
Assuming that the desired output swing is not limited by
the supply voltage rail, the IC’s output level can be calcu-
lated based on the digital input signal level and selected
amplifier gain according to the following equation:
Output signal level (dBV) = input signal level (dBFS) +
2.1dB + selected amplifier gain (dB)
where 0dBFS is referenced to 0dBV.
Click-and-Pop Suppression
The IC speaker amplifier features Maxim’s comprehen-
sive click-and-pop suppression. During startup, the click-
and-pop suppression circuitry reduces audible transient
sources internal to the device by ramping the input signal
from mute to 0dB. When entering shutdown, the differen-
tial speaker outputs immediately go into a high-imped-
ance state without creating audible click-and-pop noise.
Figure 14. EMI with 12in of Speaker Cable and No Output
Filtering
Table 7. Gain Selection
GAIN GAIN (dB)
Connect to GND through
100kI Q5% resistor
15
Connect to GND 12
Unconnected 9
Connect to V
DD
6
Connect to V
DD
through
100kI Q5% resistor
3
FREQUENCY (MHz)
EMISSIONS LEVEL (dBµV/m)
900800600 700200 300 400 500100
10
30
50
70
90
-10
0 1000