MAX9723 데이터 시트보기 (PDF) - Maxim Integrated
부품명
상세내역
제조사
MAX9723 Datasheet PDF : 26 Pages
| |||
MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I2C
Click-and-Pop Suppression
The output-coupling capacitor is a major contributor of
audible clicks and pops in conventional single-supply
headphone amplifiers. The amplifier charges the coupling
capacitor to its output bias voltage at startup. During shut-
down the capacitor is discharged. This charging and dis-
charging results in a DC shift across the capacitor, which
appears as an audible transient at the speaker. Since the
MAX9723 headphone amplifier does not require output-
coupling capacitors, no audible transients occur.
Additionally, the MAX9723 features extensive click-and-
pop suppression that eliminates any audible transient
sources internal to the device. The Power-Up/Power-
Down Waveform in the Typical Operating Characteristics
shows that there are minimal transients at the output upon
startup or shutdown.
In most applications, the preamplifier driving the MAX9723
has a DC bias of typically half the supply. The input-coupling
capacitor is charged to the preamplifier’s bias voltage
through the MAX9723’s input impedance (RIN) during start-
up. The resulting voltage shift across the capacitor creates
an audible click/pop. To avoid clicks/pops caused by the
input filter, delay the rise of SHDN by at least 4 time con-
stants, 4 x RIN x CIN, relative to the start of the preamplifier.
BassMax (Bass Boost)
Typical headphones do not have a flat-frequency response.
The small physical size of the diaphragm does not allow the
headphone speaker to efficiently reproduce low frequen-
cies. This physical limitation results in attenuated bass
response. The MAX9723 includes a bass boost feature
that compensates for the headphone’s poor bass response
by increasing the amplifier gain at low frequencies.
The DirectDrive output of the MAX9723 has more head-
room than typical single-supply headphone amplifiers.
This additional headroom allows boosting the bass fre-
quencies without the output-signal clipping.
Program the BassMax gain and cutoff frequency with
external components connected between OUT_ and BB_
(see the Functional Diagram/Typical Operating Circuit).
Use the I2C-compatible interface to program the com-
mand register to enable/disable the BassMax circuit.
BB_ is connected to the noninverting input of the output
amplifier when BassMax is enabled. BB_ is pulled to
SGND when BassMax is disabled. The typical application
of the BassMax circuit involves feeding a lowpass version
of the output signal back to the amplifier. This is realized
MAX9723
R
R
AUDIO
INPUT
BassMax
ENABLE
OUT_
BB_
R1
R2
C3
Figure 2. BassMax External Connections
using positive feedback from OUT_ to BB_. Figure 2
shows the connections needed to implement BassMax.
Maximum Gain Control
The MAX9723A and MAX9723B have selectable maxi-
mum gains of -5dB or 0dB (see Table 5) while the
MAX9723C and MAX9723D have selectable maximum
gains of +1dB or +6dB (see Table 6). Bit 5 in the command
register selects between the two maximum gain settings.
Volume Control
The MAX9723 includes a 32-level volume control that
adjusts the gain of the output amplifiers according to
the code contained in the command register. Volume is
programmed through the command register bits [4:0].
Tables 7–10 show all of the available gain settings for the
MAX9723A–MAX9723D. The mute attenuation is typically
better than 100dB when driving a 32Ω load.
Serial Interface
The MAX9723 features an I2C/SMBus-compatible, 2-wire
serial interface consisting of a serial data line (SDA) and
a serial clock line (SCL). SDA and SCL facilitate commu-
nication between the MAX9723 and the master at clock
rates up to 400kHz. Figure 3 shows the 2-wire interface
timing diagram. The MAX9723 is a receive-only slave
device relying on the master to generate the SCL signal.
The MAX9723 cannot write to the SDA bus except to
acknowledge the receipt of data from the master. The
www.maximintegrated.com
Maxim Integrated │ 11
Share Link: 