MAX9723
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 pro-
grammed by B5. Tables 7–10 list all the possible gain
settings for the MAX9723. Figures 7–10 show the vol-
ume 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 maximum 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:
where T
J(MAX)
is +150°C, T
A
is the ambient tempera-
ture, 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 dissipa-
tion, reduce V
DD
, increase load impedance, decrease
the ambient temperature, or add heatsinking. Large
output, supply, and ground traces decrease θ
JA
, allow-
ing 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 clip-
ping will occur if the output signal is greater than the
dynamic range of the system. The DirectDrive architec-
ture 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 determine the peak output
voltage that causes 1% THD+N for a given load.
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:
where V
IN_(P-P)
is the largest peak voltage that can be
amplified without clipping, and A
V
is the voltage gain of
