MAX9722AETE+G Maxim Integrated Products, MAX9722AETE+G Datasheet - Page 9

• 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

Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typi-
cally half the supply) for maximum dynamic range.
Large coupling capacitors are needed to block this DC
bias from the headphone. Without these capacitors, a
significant amount of DC current flows to the head-
phone, resulting in unnecessary power dissipation and
possible damage to both the headphone and the head-
phone amplifier.
Maxim’s DirectDrive architecture uses a charge pump to
create an internal negative supply voltage, allowing the
MAX9722A/MAX9722B outputs to be biased about
GND. With no DC component, there is no need for the
large DC-blocking capacitors. Instead of two large
(220µF, typ) tantalum capacitors, the MAX9722A/
MAX9722B charge pump requires two small ceramic
capacitors, conserving board space, reducing cost, and
improving the frequency response of the headphone
amplifier. See the Output Power vs. Load Resistance
graph in the Typical Operating Characteristics for
details of the possible capacitor sizes. There is a low
DC voltage on the amplifier outputs due to amplifier off-
set. However, the offset of the MAX9722A is typically
0.5mV, which, when combined with a 32Ω load, results
in less than 15.6µA of DC current flow to the head-
phones. Previous attempts to eliminate the output-cou-
pling capacitors involved biasing the headphone return
(sleeve) to the DC-bias voltage of the headphone ampli-
fiers. This method raises some issues:
• The sleeve is typically grounded to the chassis.
• During an ESD strike, the amplifier’s ESD structures
• When using the headphone jack as a line out to other
• When using a combination microphone and speaker
In addition to the cost and size disadvantages of the DC-
blocking capacitors required by conventional head-
Using this biasing approach, the sleeve must be iso-
lated from system ground, complicating product
design.
are the only path to system ground. Thus, the amplifi-
er must be able to withstand the full ESD strike.
equipment, the bias voltage on the sleeve may con-
flict with the ground potential from other equipment,
resulting in possible damage to the amplifiers.
headset, the microphone typically requires a GND
reference. The amplifier DC bias on the sleeve con-
flicts with the microphone requirements (Figure 3).
Stereo Headphone Amplifiers with Shutdown
5V, Differential Input, DirectDrive, 130mW
_______________________________________________________________________________________
Low-Frequency Response
DirectDrive
phone amplifiers, these capacitors limit the amplifier’s
low-frequency response and can distort the audio signal:
1) The impedance of the headphone load and the DC-
where R
C
The highpass filter is required by conventional single-
ended, single power-supply headphone amplifiers to
block the midrail DC-bias component of the audio sig-
nal from the headphones. The drawback to the filter is
that it can attenuate low-frequency signals. Larger val-
ues of C
larger, more expensive capacitors. Figure 4 shows the
relationship between the size of C
low-frequency attenuation. Note that the -3dB point for
a 16Ω headphone with a 100µF blocking capacitor is
100Hz, well within the normal audio band, resulting in
low-frequency attenuation of the reproduced signal.
Figure 3. Earbud Speaker/Microphone Combination Headset
Configuration
OUT
MICROPHONE
blocking capacitor form a highpass filter with the
-3dB point set by:
AMPLIFIER
is the value of the DC-blocking capacitor.
OUTPUT
AUDIO
AUDIO
INPUT
INPUT
OUT
L
is the impedance of the headphone and
reduce this effect but result in physically
f
-3
dB
HEADPHONE DRIVER
MICROPHONE
AMPLIFIER
=
MAX9722
2
π
R C
L OUT
1
MICROPHONE
OUT
BIAS
and the resulting
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