max9727eept Maxim Integrated Products, Inc., max9727eept Datasheet - Page 10

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

Figure 3 shows a single channel of the MAX9727 con-
figured as an inverting amplifier. External resistors R
and R
where A
R
digitally controlled potentiometer to alter the gain under
software control.
When the MAX9727 is used as a line driver to provide
outputs that feed audio equipment (notebooks, desk-
tops, receivers, and set-top boxes) with a digital-to-
analog converter (DAC) used as an audio input source,
it is often desirable to eliminate any high-frequency
quantization noise produced by the DAC output before
it reaches the load. This high-frequency noise can
cause the input stages of the line-in equipment to
exceed slew-rate limitations or create excessive EMI
emissions on the cables between devices.
In order to suppress this noise, and to provide a 2V
standard audio output level from a single 5V supply,
the MAX9727 can be configured as an active lowpass
filter. The Functional Diagram/Typical Application
Circuit shows the MAX9727 connected as 2-pole
Quad Audio Line Driver with 3V
Figure 3. Inverting Amplifier Configuration
10
F
can be either fixed or variable, allowing the use of a
______________________________________________________________________________________
IN
R
IN
V
set the voltage gain of the amplifier as follows:
is the desired voltage gain in V/V.
Inverting Amplifier Configuration
IN_-
IN_+
A
V
=
−
Active Filter Configuration
MAX9727
R
R
IN
F
R
F
OUT_
RMS
F
Rauch/Multiple Feedback filter with a passband gain of
6dB and a -3dB (below passband) cutoff frequency of
approximately 27kHz (see Figure 4 for Gain vs.
Frequency plot).
The input capacitor C
a highpass filter that removes the DC bias from an
incoming signal. The AC-coupling capacitor allows the
amplifier to bias the signal to an optimum DC level.
Assuming zero-source impedance, the -3dB point of
the highpass filter is given by:
Setting f
response of the amplifier. Use capacitors with
dielectrics that have low-voltage coefficients, such as
tantalum or aluminum electrolytic. Capacitors with high-
voltage coefficients, such as ceramics, can increase
distortion at low frequencies.
Use capacitors with an ESR of less than 100mΩ for
optimum performance. Low-ESR ceramic capacitors
minimize the output resistance of the charge pump. For
best performance over the extended temperature
range, select capacitors with an X7R dielectric.
Figure 4. MAX9727 Active Filter Gain vs. Frequency
-3dB
-12
-15
-3
-6
-9
9
6
3
0
1
ACTIVE FILTER GAIN vs. FREQUENCY
RMS
too high affects the low-frequency
Charge-Pump Capacitor Selection
f
−
3
IN
dB
FREQUENCY (kHz)
, in conjunction with R
=
Output
2π
10
R C
IN IN
1
100
Input Filter
IN
, forms