Datasheet

The MAX9723A and MAX9723B have a maximum
gain setting of -5dB or 0dB, while the MAX9723C and
MAX9723D have a maximum gain setting of +1dB or
+6dB. B5 in the command register programs the maxi-
mum gain (see Tables 5 and 6).
Adjust the MAX9723’s amplifier gain with the volume
control bits [4:0]. The gain is adjustable to one of 32 steps
ranging from full mute to the maximum gain programmed
by B5. Tables 7–10 list all the possible gain settings for
the MAX9723. Figures 7–10 show the volume control
transfer functions for the MAX9723.
Power-On Reset
The contents of the MAX9723’s command register at
power-on are shown in Table 11.
Applications Information
Power Dissipation and Heat Sinking
Linear power amplifiers can dissipate a significant amount
of power under normal operating conditions. The maxi-
mum power dissipation for each package is given in the
Absolute Maximum Ratings section under Continuous
Power Dissipation or can be calculated by the following
equation:
J(MAX) A
D(MAX)
JA
TT
P
−
=
θ
where T
J(MAX)
is +150°C, T
A
is the ambient temperature,
and θ
JA
is the reciprocal of the derating factor in °C/W as
specified in the Absolute Maximum Ratings section. For
example, θ
JA
for the thin QFN package is +59°C/W.
The MAX9723 has two power dissipation sources, the
charge pump and the two output amplifiers. If the power
dissipation exceeds the rated package dissipation, reduce
V
DD
, increase load impedance, decrease the ambient
temperature, or add heatsinking. Large output, supply,
and ground traces decrease θ
JA
, allowing more heat to be
transferred from the package to surrounding air.
Output Dynamic Range
Dynamic range is the difference between the noise
floor of the system and the output level at 1% THD+N.
It is essential that a system’s dynamic range be known
before setting the maximum output gain. Output clipping
will occur if the output signal is greater than the dynamic
range of the system. The DirectDrive architecture of the
MAX9723 has increased dynamic range compared to
other single-supply amplifiers.
Use the THD+N vs. Output Power in the Typical Operating
Characteristics to identify the system’s dynamic range.
Find the output power that causes 1% THD+N for a given
load. This point will indicate what output power causes the
output to begin to clip. Use the following equation to deter-
mine the peak output voltage that causes 1% THD+N for
a given load.
OUT_(P P) OUT_1% L
V 2 2(P R )
−
= ×
where P
OUT_1%
is the output power that causes 1%
THD+N, R
L
is the load resistance, and V
OUT_(P-P)
is
the peak output voltage. After V
OUT_(P-P)
is identified,
determine the peak input voltage that can be amplified
without clipping:
V
OUT_(P P)
IN_(P P)
A
20
V
V
10
−
−



=
where V
IN_(P-P)
is the largest peak voltage that can be
amplified without clipping, and A
V
is the voltage gain
Figure 6. Write Data Format Example
Table 5. MAX9723A and MAX9723B
Maximum Gain Control
Table 6. MAX9723C and MAX9723D
Maximum Gain Control
MAXIMUM GAIN (dB) B5
-5 0
0 1
MAXIMUM GAIN (dB) B5
+1 0
+6 1
S ACK 0
ACKNOWLEDGE FROM MAX9723
R/W
ACKNOWLEDGE
FROM MAX9723
B7 B6
B5 B4
B3 B2
COMMAND BYTE IS STORED ON
RECEIPT OF STOP CONDITION
ACK P
B1 B0
SLAVE ADDRESS COMMAND BYTE
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I
2
C
www.maximintegrated.com
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