MAX9853 Maxim Integrated Products, MAX9853 Datasheet - Page 35

• Manufacturer Part Number: MAX9853
• Description: (MAX9851 / MAX9853) Stereo Audio CODECs
• Manufacturer: Maxim Integrated Products

The MAX9851/MAX9853 operate from either a 13MHz
or 26MHz master input clock (MCLK). 16kHz voice
mode requires a 26MHz clock. The quality of the clock
signal has a direct relationship with the dynamic range
performance of the data converters. Clock jitter below
100ps
mance figures.
The MAX9851/MAX9853 make extensive use of MCLK
for all chip functions. The digital circuitry and Class D
amplifiers require a master clock to operate.
Once the MAX9851/MAX9853 are initialized, MCLK is
not required during modes where the ADC and DAC
are disabled (for instance, playing line inputs through
the headphone outputs). However, MCLK needs to be
applied for a short period of time (> 1ms) after
power-on to initialize volume control circuitry—this
is only once per power-on.
The MAX9851/MAX9853 provide mono voiceband filter-
ing for both output and input digital audio signals on the
primary interface. Set ABPE to 1 (register 0x07, bit B5) to
enable the highpass component of the voiceband filtering
on the output of the ADC. Similarly, set DBPE to 1 (regis-
ter 0x07, bit B4) to enable the highpass component of the
voiceband filtering for incoming data on the primary digi-
tal audio interface. Voiceband filtering is available on
either interface for outgoing digital audio from the ADC,
and incoming data only on the primary S1 digital audio
interface. The voiceband filters only operate when the
MAX9851/MAX9853 are configured in voice mode. The
DAC and ADC voiceband filters are identical, with sam-
ple-rate-specific corner frequencies. Operating in 8kHz
voice mode, the filter passband extends from 130Hz to
3.5kHz. In 16kHz voice mode, the filter passband extends
from 260Hz to 7kHz. Stopband attenuation is greater
than 28dB for low frequency and 75dB for high frequen-
cies and the lowpass cutoff frequency is below f
Stereo Audio CODECs with Microphone, DirectDrive
Headphones, Speaker Amplifiers, or Line Outputs
RMS
is necessary to maintain maximum perfor-
______________________________________________________________________________________
Voiceband Filters
Internal Timing
S
/ 2.
See the Typical Operating Characteristics for filter char-
acteristics.
The MAX9851/MAX9853 provide two single-ended
audio line inputs for mixing with analog audio from
either the ADC record path or to the DAC playback
path. Each line input amplifier has a programmable-
gain function controlled by PGAL1 and PGAL2 (regis-
ters 0x0E and 0x0F). The gain is adjustable over the
+30dB to -32dB range in 2dB increments.
The MAX9851/MAX9853 headphone and receiver ampli-
fiers make use of Maxim’s patented DirectDrive architec-
ture to create ground-biased outputs as shown in Figure
5. Traditional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage, typical-
ly half the supply. Large coupling capacitors are typically
needed to block this DC bias from the headphone.
Without these capacitors, a significant amount of DC cur-
rent flows to the headphone, resulting in unnecessary
power dissipation and possible damage to both head-
phone and headphone amplifier. The DirectDrive archi-
tecture uses a charge pump to create an internal
negative supply voltage. This allows the MAX9851/
MAX9853 headphone and receiver outputs to be biased
about ground, almost doubling the dynamic range while
operating from a single supply. With no DC component,
there is no need for the large DC-blocking capacitors.
Instead of two large (33µF to 330µF) capacitors, the
MAX9851/MAX9853 charge pump requires only two
small ceramic capacitors (0.22µF and 1µF), conserving
board space, reducing cost, improving the frequency
response, and THD of the headphone amplifier. In addi-
tion to the cost and size disadvantages, the DC-blocking
capacitors required by conventional headphone ampli-
fiers limit low-frequency response and decrease PSRR
performance. Some dielectrics can significantly distort
the audio signal.
and Receiver Amplifiers
DirectDrive Headphone
Line Inputs
35