Datasheet
Maxim Integrated
│
138
MAX98090 Ultra-Low Power Stereo Audio Codec
www.maximintegrated.com
Efcient Class D Speaker Output Driver
A Class D amplifier offers much higher efficiency than
a Class AB amplifier. The high efficiency is due to the
switching operation of the output stage transistors. In a
Class D amplifier, the output transistors act as current
steering switches and consume negligible additional
power. Any power loss associated with a Class D output
stage is primarily due to the loss in the MOSFET on-
resistance, and the baseline quiescent current overhead.
For comparison, the theoretical best-case efficiency of a
linear amplifier is 78%. However, that efficiency is only
possible at peak output power conditions. Under normal
operating levels (typical music reproduction levels), effi-
ciency often falls below 30%. Under the same conditions,
the device’s differential Class D speaker output amplifier
still exhibits 80% efficiency.
By default, the Class D output switching clocks are inde-
pendently generated for the left and right channels. With
slave mode enabled, the right channel becomes a slave
to the left channel and uses the same clock (Table 65).
In slave mode, the switching scheme is synchronous. As
a result, slave mode operation eliminates potential beat
tones that can occur with asynchronous stereo Class D
switching.
Traditional Class D amplifiers often require the use of
external LC filters and/or shielding to meet EN55022B
and FCC electromagnetic-interference (EMI) regulation
standards. Maxim’s patented active emissions limiting
edge-rate control circuitry reduces EMI emissions. This
allows the device to drive both 4Ω and 8Ω without any
additional output filtering. The filterless Class D outputs
are designed for typical applications where the trace
length to the speakers is short and has a low series
resistance. See the Filterless Class D Speaker Operation
section for application level details.
Analog Class-H Headphone Output
The stereo headphone output driver has a flexible input
mixer, programmable gain stage, an integrated charge
pump, and a ground referenced DirectDrive Class H
output amplifier (Figure 36). The headphone output
amplifier is capable of driving both 16Ω and 32Ω ground-
referenced headphone loads.
Figure 36. DirectDrive Headphone Output Functional Diagram
DACR
DACL
MIC 1
MIC 2
LINE A
LINE B
DACR
DACL
MIC 1
MIC 2
LINE A
LINE B
ANALOG
INPUT
DRIVERS
DACLEN DACRENDACHP
PERFMODE
DAC
LEFT
DAC
RIGHT
HEADPHONE
DIRECT DRIVE
CHARGE PUMP
MIXHPR[5:0]
MIXHPRG[1:0]
HP
RIGHT
MIXER
HP
LEFT
MIXER
MIXHPLSEL
MIXHPRSEL
HP
LEFT
MUX
HPVOLL[4:0]
HPLM
HPLEN
-67dB TO 3dB
-67dB TO 3dB
-12dB TO 0dB
HP
RIGHT
MUX
-12dB TO 0dB
HEADPHONE
LEFT PGA
HEADPHONE
RIGHT PGA
HPVOLR[4:0]
HPRM
HPREN
MIXHPL[5:0]
MIXHPLG[1:0]
HPSNS
HPL
HPR
HPVDD
HPGND
C1P
C1N CPVDD CPVSS
FLEXSOUND
TECHNOLOGY
DSP
SPEAKER/RECEIVER/
LINE OUT
MAX98090
ZDEN
VS2EN
ZSEN