MAX9722AETE+G Maxim Integrated Products, MAX9722AETE+G Datasheet - Page 14

• Manufacturer Part Number: MAX9722AETE+G
• Description: IC AMP AUDIO .13W STER AB 16TQFN
• Manufacturer: Maxim Integrated Products
• Series: DirectDrive™r
• Type: Class ABr

Specifications of MAX9722AETE+G

• Output Type: Headphones, 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 130mW x 2 @ 32 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Features: Depop, Differential Inputs, Short-Circuit and Thermal Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 16-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MAX9722AETE+G47; MAX9722AETE+G47

such as the headphone socket used as a line output to
a home hi-fi system. In the upper diagram, any differ-
ence between the two GND references (represented by
V
cable between the two devices. This can cause noise
pickup at the receiver due to the potential divider
action of the audio screen cable impedance and the
GND wiring of the amplifier.
Introducing impedance between the jack socket and
GND of the notebook helps (as shown in the lower dia-
gram). This has the following effect:
Current flow (from GND potential differences) in the
cable screen is reduced, which is a safety issue.
It allows the MAX9722A/MAX9722B differential sensing
to reduce the GND noise seen by the receiver (amplifier).
The other side effect is that the differential headphone
jack sensing corrects the headphone crosstalk (from
introducing the resistance on the jack GND return).
Only one channel is depicted in Figure 9.
Figure 9 has some example numbers for resistance,
but the audio designer has control over only one series
resistance applied to the headphone jack return. Note
that this resistance can be bypassed for ESD purposes
at frequencies much higher than audio if required. The
upper limit for this added resistance is the amount of
output swing the headphone amplifier tolerates when
driving low-impedance loads. Any headphone return
current appears as a voltage across this resistor.
Low-profile piezoelectric speakers can provide quality
sound for portable electronics. However, piezoelectric
speakers typically require large voltage swings
(>8V
sound pressure levels. Power sources in portable
devices are usually low voltage in nature. Operating
from batteries, conventional amplifiers cannot provide
sufficient voltage swing to drive a piezoelectric speak-
er. However, the MAX9722’s DirectDrive architecture
can be configured to drive a piezoelectric speaker with
up to 12V
The stereo MAX9722 features an inverting charge
pump that takes the positive +5V supply and creates a
negative -5V supply. Each output of the MAX9722 can
swing 6V
electric speaker. If a higher output voltage is desired,
configuring the MAX9722A as a bridge-tied load (BTL)
amplifier (Figure 10) doubles the maximum output
swing as seen by the load to 12V
ration, the right channel of the MAX9722 serves as the
master amplifier, setting the gain of the device, driving
one side of the speaker, and providing signal to the left
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
14
NOISE
P-P
______________________________________________________________________________________
) causes current to flow through the screen of
) across the speaker element to produce usable
P-P
P-P
. This may be sufficient to drive a piezo-
while operating from a single 5V supply.
Piezoelectric Speaker Amplifier
P-P
. In a BTL configu-
channel. The left channel is configured as a unity-gain
follower, inverting the output of the right channel and
driving the other leg of the speaker. Use precision
resistors to set the gain of the left channel to ensure low
distortion and good matching.
The MAX9722 was tested with a Panasonic WM-R57A
piezoelectric speaker, and the resulting THD+N curves
are shown (Figures 11 and 12). Note in both graphs, as
frequency increases, the THD+N increases. This is due
Figure 10. MAX9722 BTL Configuration
Figure 11. MAX9722 THD+N vs. Output Voltage
AUDIO
INPUT
1μF
0.1000
0.0100
0.0010
0.0001
100
10kΩ
10
1
0
TOTAL HARMONIC DISTORTION PLUS
V
A
OUTPUTS DRIVING
PIEZOELECTRIC SPEAKER
DD
V
= -1V/V
NOISE vs. OUTPUT VOLTAGE
= 5V
2
f = 100Hz
f = 20Hz
INR
f = 1kHz
4
OUTPUT POWER (mW)
MAX9722A
6
10kΩ
8
10
OUTR
OUTL
INL
12
14
10kΩ
10kΩ