MAX9726 Maxim Integrated Products, MAX9726 Datasheet - Page 10

• Manufacturer Part Number: MAX9726
• Description: Headphone Amplifier
• Manufacturer: Maxim Integrated Products

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DirectDrive, Headphone Amplifier with
BassMax, I
The MAX9726 stereo headphone amplifier features
Maxim’s patented DirectDrive architecture, eliminating
the large output-coupling capacitors required by con-
ventional single-supply headphone amplifiers. The
MAX9726 consists of two 105mW Class AB headphone
amplifiers, two adjustable gain preamplifiers, hard-
ware/software shutdown control, inverting charge
pump, integrated 64-level volume control, BassMax fea-
ture, comprehensive click-and-pop suppression circuit-
ry, and an I
Functional Diagram/Typical Operating Circuit). A nega-
tive power supply (PV
ing the positive supply (V
from V
amplifiers to almost twice that of other single-supply
amplifiers, increasing the total available output power.
High PSRR topologies eliminate the need for an external
voltage regulator.
An I
munication between the MAX9726 and a microcon-
troller. The internal command register controls the
shutdown status of the MAX9726, enables the BassMax
circuitry, and sets the volume level (see the Volume
Control section). The MAX9726’s BassMax circuitry
improves audio reproduction by boosting the bass
response of the amplifier, compensating for any low-
frequency attenuation introduced by the headphone.
External components set the MAX9726’s overall gain
allowing for custom gain settings (see the Gain-Setting
Components section). Amplifier volume is digitally pro-
grammable to any one of 64 levels.
Traditional 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 head-
phone amplifier. In addition to the cost and size disad-
vantages, the DC-blocking capacitors required by
conventional headphone amplifiers limit low-frequency
response and can distort the audio signal.
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2
______________________________________________________________________________________
C-/SMBus-compatible interface allows serial com-
DD
and PV
2
C-/SMBus-compatible interface (see the
SS
increases the dynamic range of the
SS
Detailed Description
) is created internally by invert-
DD
2
C, Volume and Gain Control
). Powering the amplifiers
DirectDrive
Maxim’s patented DirectDrive architecture uses a
charge pump to create an internal negative supply volt-
age. This allows the MAX9726 headphone amplifier
outputs to be biased about ground, almost doubling
the dynamic range while operating from a single supply
(see Figure 1). With no DC component, there is no
need for the large DC-blocking capacitors. Instead of
two large (up to 220µF) tantalum capacitors, the
MAX9726 charge pump requires only two small 1µF
ceramic capacitors, conserving board space, reducing
cost, and improving the frequency response of the
headphone amplifier. See the Output Power vs.
Charge-Pump Capacitance and Load Resistance
graphs in the Typical Operating Characteristics for
details of the possible capacitor sizes.
Figure 1. Traditional Amplifier Output vs. MAX9726 DirectDrive
Output
V
-V
V
GND
DD
GND
*
V
DD
DD
V
AND TO LIMIT POWER DISSIPATION.
DD
/2
DD
V
V
*
*
OUT
OUT
IS INTERNALLY LIMITED TO ±2.5V DUE TO ABSOLUTE MAXIMUM RATINGS
CONVENTIONAL DRIVER-BIASING SCHEME
DirectDrive BIASING SCHEME
2V
V
DD
DD
*