MAX98088 Datasheet, PDF (56/123 Pages) Maxim Integrated Products – Stereo Audio Codec with FLEXSOUND Technology

Stereo Audio Codec
with FLEXSOUND Technology
Detailed Description
The MAX98088 is a fully integrated stereo audio codec
with FLEXSOUND technology and integrated amplifiers.
Two differential microphone amplifiers can accept sig-
nals from three analog inputs. One input can be retasked
to support two digital microphones. Any combination of
two microphones (analog or digital) can be recorded
simultaneously. The analog signals are amplified up
to 50dB and recorded by the stereo ADC. The digital
record path supports voice filtering with selectable
preset highpass filters and high stopband attenuation
at fS/2. An automatic gain control (AGC) circuit moni-
tors the digitized signal and automatically adjusts the
analog microphone gain to make best use of the ADC’s
dynamic range. A noise gate attenuates signals below
the user-defined threshold to minimize the noise output
by the ADC.
The IC includes two analog line inputs. One of the line
inputs can be optionally retasked as a third analog micro-
phone input. Both line inputs support either stereo single-
ended input signals or mono differential signals. The line
inputs are preamplified and then routed either to the ADC
for recording or to the output amplifiers for playback. The
single-ended line inputs signals from INA1 and INA2 can
bypass the PGAs, and be connected directly to the ADC
input to provide the best dynamic range.
Integrated analog switches allow two differential micro-
phone signals to be routed out the third microphone
input to an external device. This eliminates the need
for an external analog switch in systems that have two
devices recording signals from the same microphone.
Through two digital audio interfaces, the device can
transmit one stereo audio signal and receive two stereo
audio signals in a wide range of formats including I²S,
PCM, and up to four mono slots in TDM. Each interface
can be connected to either of two audio ports (S1 and
S2) for communication with external devices. Both audio
interfaces support 8kHz to 96kHz sample rates. Each
input signal is independently equalized using 5-band
parametric equalizers. A multiband automatic level
control (ALC) boosts signals by up to 12dB. One signal
path additionally supports the same voiceband filtering
as the ADC path.
The IC includes a stereo Class D speaker amplifier, a
high-efficiency Class H stereo headphone amplifiers,
and a differential receiver amplifier that can be config-
ured as a stereo line output.
When the receiver amplifier is disabled, analog switches
allow RECP/RXINP and RECN/RXINN to be reused for
signal routing. In systems where a single transducer is
used for both the loudspeaker and receiver, an exter-
nal receiver amplifier can be routed to the left speaker
through RECP/RXINP and RECN/RXINN, bypassing the
Class D amplifier, to connect to the loudspeaker. If the
internal receiver amplifier is used, then leave RECP/
RXINP and RECN/RXINN unconnected. In systems
where an external amplifier drives both the receiver and
the MAX98088/MAX98089’s input, one of the differential
signals can be disconnected from the receiver when
not needed by passing it through the analog switch that
connects RECP/RXINP to RECN/RXINN.
The stereo Class D amplifier provides efficient amplifi-
cation for two speakers. The amplifier includes active
emissions limiting to minimize the radiated emissions
(EMI) traditionally associated with Class D. In most
systems, no output filtering is required to meet standard
EMI limits.
To optimize speaker sound quality, the IC includes an
excursion limiter, a distortion limiter, and a power limiter.
The excursion limiter is a dynamic highpass filter with
variable corner frequency that increases in response
to high signal levels. Low-frequency energy typically
causes more distortion than useful sound at high sig-
nal levels, so attenuating low frequencies allows the
speaker to play louder without distortion or damage. At
lower signal levels, the filter corner frequency reduces
to pass more low frequency energy when the speaker
can handle it. The distortion limiter reduces the volume
when the output signal exceeds a preset distortion level.
This ensures that regardless of input signal and battery
voltage, excessive distortion is never heard by the user.
The power limiter monitors the continuous power into the
loudspeaker and lowers the signal level if the speaker is
at risk of overheating.
The stereo Class H headphone amplifier uses a dual-
mode charge pump to maximize efficiency while out-
putting a ground-referenced signal. This eliminates the
need for DC-blocking capacitors or a midrail bias for the
headphone jack ground return. Ground sense reduces
output noise caused by ground return current.
The IC integrates jack detection allowing the detection of
insertion and removal of accessories.
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