Datasheet

MAX9724A/MAX9724B
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
______________________________________________________________________________________ 13
Lineout Amplifier and Filter Block
The MAX9724A can be used as an audio line driver
capable of providing 2V
RMS
into 10kΩ loads with a sin-
gle 5V supply (see Figure 4 for the RMS Output Voltage
vs. Supply Voltage plot). 2V
RMS
is a popular audio line
level, first used in CD players, but now common in DVD
and set-top box (STB) interfacing standards. A 2V
RMS
sinusoidal signal equates to approximately 5.7V
P-P
,
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
RMS
from a 5V supply, or
even 3.3V supply, can often simplify power-supply
design in some systems.
When the MAX9724A 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.
LEFT
AUDIO
INPUT
RIGHT
AUDIO
INPUT
OUTL
INL
INR
OUTR
MAX9724A
7.5kΩ 7.5kΩ
7.5kΩ 7.5kΩ
15kΩ
10kΩ
10kΩ
15kΩ
1.2nF
1.2nF
220pF
220pF
LINE IN DEVICE
STEREO
DAC
1μF
1μF
Figure 5. MAX9724A Line Out Amplifier and Filter Block Configuration
RMS OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
RMS OUTPUT VOLTAGE (V)
5.04.54.03.53.0
2.0
2.5
3.0
3.5
1.5
2.5 5.5
R
L
= 10kΩ
1% THD+N
f
IN
= 1kHz
R
L
= 1kΩ
1% THD+N
LIMITED BY
ABS. MAXIMUM
RATINGS
Figure 4. RMS Output Voltage vs. Supply Voltage