max9728a Maxim Integrated Products, Inc., max9728a Datasheet - Page 10

• Manufacturer Part Number: max9728a
• Description: 60mw, Directdrive, Stereo Headphone Amplifier With Shutdown
• Manufacturer: Maxim Integrated Products, Inc.

The MAX9728A can be used as an audio line driver
capable of providing 2V
gle 5V supply (see Figure 3 for the RMS Output Voltage
vs. Supply Voltage plot). 2V
level, first used in CD players, but now common in DVD
and set-top box (STB) interfacing standards. A 2V
sinusoidal signal equates to approximately 5.7V
which means that the audio system designer cannot
simply run the lineout stage from a (typically common)
5V supply—the resulting output swing would be inade-
quate. A common solution to this problem is to use op
amps driven from split supplies (±5V typically), or to use
a high-voltage supply rail (9V to 12V). This can mean
adding extra cost and complexity to the system power
supply to meet this output level requirement. Having the
ability to derive 2V
plify power-supply design in some systems.
When the MAX9728A is used as a line driver to provide
outputs that feed stereo equipment (receivers, STBs,
notebooks, and desktops) with a digital-to-analog con-
verter (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 lim-
itations or create excessive EMI emissions on the
cables between devices.
To suppress this noise, and to provide a 2V
dard audio output level from a single 5V supply, the
MAX9728A can be configured as a line driver and
active lowpass filter. Figure 4 shows the MAX9728A
connected as 2-pole Rauch/multiple feedback filter with
a passband gain of 6dB and a -3dB (below passband)
cutoff frequency of approximately 27kHz (see Figure 5
for the Gain vs. Frequency plot).
Proper layout and grounding are essential for optimum
performance. Connect PGND and SGND together at a
single point on the PC board. Connect PV
and bypass with a 1µF capacitor. Place the power-sup-
ply bypass capacitor and the charge-pump hold
capacitor as close to the MAX9728 as possible. Route
PGND and all traces that carry switching transients
away from SGND and the audio signal path. The thin
QFN package features an exposed paddle that
improves thermal efficiency. Ensure that the exposed
paddle is electrically isolated from PGND, SGND,
and V
when the board layout dictates that the exposed
paddle cannot be left floating.
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
10
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DD
. Connect the exposed paddle to SV
Lineout Amplifier and Filter Block
RMS
from a 5V supply can often sim-
RMS
Layout and Grounding
RMS
into 10kΩ loads with a sin-
is a popular audio line
SS
RMS
to SV
SS
stan-
only
RMS
P-P
SS
,
Figure 2. Gain Setting for the MAX9728A
Figure 3. RMS Output Voltage vs. Supply Voltage
AUDIO
AUDIO
INPUT
RIGHT
INPUT
LEFT
R
R
4.1
3.9
3.7
3.5
3.3
3.1
2.9
2.7
2.5
IN
IN
4.5
f
IN
R
1% THD+N
L
= 1kHz
= 10kΩ
INL
INR
RMS OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
MAX9728A
R
R
F
F
5.0
R
1% THD+N
OUTL
OUTR
L
= 1kΩ
5.5