max9727eept Maxim Integrated Products, Inc., max9727eept Datasheet - Page 9

• Manufacturer Part Number: max9727eept
• Description: Max9727 Quad Audio Line Driver With 3vrms Output
• Manufacturer: Maxim Integrated Products, Inc.

The MAX9727 features a low-power shutdown mode
that reduces quiescent current consumption to less
than 0.1µA and extends battery life for portable appli-
cations. Drive SHDN low to disable the amplifiers and
the charge pump. In shutdown mode, each amplifier’s
output resistance is high impedance to small signals.
The resulting output resistance seen by the load is
determined by the series combination of the amplifier’s
external gain-setting resistors in parallel with the ampli-
fier’s shutdown output resistance.
In conventional single-supply audio amplifiers, the out-
put-coupling capacitor contributes significantly to audi-
ble clicks and pops. Upon startup, the amplifier charges
the coupling capacitor to its bias voltage, typically half
the supply. Likewise, on shutdown, the capacitor is dis-
charged. This results in a DC shift across the capacitor,
which appears as an audible transient at the speaker
connected to the output of the power amplifier of the
audio system. Since the MAX9727 does not require out-
put-coupling capacitors, this problem does not arise.
Additionally, the MAX9727 features extensive click-and-
pop suppression that eliminates any audible transient
sources internal to the device.
In some applications, the output of the device driving
the MAX9727 may have a DC bias. At startup, the
input-coupling capacitor is charged to the input
device’s DC-bias voltage through the input and feed-
back resistors of the MAX9727, resulting in a DC shift
across the capacitor and an audible click/pop. Delay
the rise of SHDN 4 to 5 time constants based on R
and C
input device, to eliminate clicks-and-pops caused by
the input filter.
The MAX9727 works in many standard op-amp config-
urations such as inverting, noninverting, voltage follow-
er, summing, difference, active filters, and many others.
No special design considerations are required. The
DirectDrive architecture of the MAX9727 simplifies
many circuits due to the ground-referenced outputs.
IN
(4 x R
Quad Audio Line Driver with 3V
Applications Information
IN
_______________________________________________________________________________________
x C
Click-and-Pop Suppression
IN
Amplifier Configurations
), relative to the startup of the
Shutdown Mode
IN
Figure 2 shows a single channel of the MAX9727 con-
figured as a differential input amplifier. A differential
input offers improved noise immunity over a single-
ended input. In systems that include high-speed digital
circuitry, high-frequency noise can couple into the
amplifier’s input traces. The signals appear at the
amplifier’s inputs as common-mode noise. A differential
input amplifier amplifies the difference of the two
inputs, and signals common to both inputs are sub-
tracted out. When configured for differential inputs, the
voltage gain of the MAX9727 is set by:
where A
be equal to R
The common-mode rejection ratio (CMRR) is limited by
the external resistor-matching. Ideally, to achieve the
highest possible CMRR the following condition should
be met:
Figure 2. Differential Input Configuration
R
R
IN1
V
IN2
is the desired voltage gain in V/V. R
R
IN2
F2
, and R
IN_-
IN_+
R
Differential Input Configuration
R
A
F1
IN
F
OUT_ =
R
V
IN1
1
1
must be equal to R
=
= R
=
RMS
R
R
MAX9727
IN2
R
R
R
R
IN
F
F1
IN
IN1
, R
F
1
R
1
2
F1
F1
2
(IN_ + - IN_-)
= R
F2
Output
OUT_
F2
IN1
.
must
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