Max9729, Detailed description, Pin description (continued) – Rainbow Electronics MAX9729 User Manual

Page 10

MAX9729

Detailed Description

The MAX9729 stereo headphone amplifier features
Maxim’s patented DirectDrive architecture, eliminating
the large output-coupling capacitors required by con-
ventional single-supply headphone amplifiers. The
MAX9729 consists of two 52mW Class AB headphone
amplifiers, 3:1 stereo input multiplexer/mixer, two
adjustable gain preamplifiers, a dedicated beep ampli-
fier with independent gain control, hardware/software
shutdown control, inverting charge pump, integrated
32-level volume control, BassMax circuitry, comprehen-
sive click-and-pop suppression circuitry, and an
I

C/SMBus-compatible interface (see the

Functional

Diagram/Typical Operating Circuit

). A negative power

supply (PV

) is created internally by inverting the posi-

tive supply (PV

). Powering the amplifiers from V

and PV

increases the dynamic range of the amplifiers

to almost twice that of other single-supply amplifiers,
increasing the total available output power.

An I

C/SMBus-compatible interface allows serial com-

munication between the MAX9729 and a microcon-

troller. The MAX9729’s slave address is programmed to
one of two different values using the ADD input allowing
two MAX9729 ICs to share the same bus (see Table 1).
The internal command registers control the shutdown
mode of the MAX9729, select/mix input signal sources,
enable the BassMax circuitry, headphone and beep
amplifier gains, and set the volume level (see Table 2).
The MAX9729’s BassMax circuitry improves audio
reproduction by boosting the bass response of the
amplifier, compensating for any low-frequency attenua-
tion introduced by the headphone. External compo-
nents set the MAX9729’s overall gain allowing for
custom gain settings (see the

BassMax Gain-Setting

Components

section).

DirectDrive

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-

Stereo Headphone Amplifier with BassMax,
Volume Control, and Input Mux

______________________________________________________________________________________

Pin Description (continued)

PIN

NAME

FUNCTION

BMR

Right BassMax Input. Connect an external passive network between OUTR and BMR to apply bass
boost to the right-channel output. See the BassMax Gain-Setting Components section. Connect BMR to
SGND if BassMax is not used.

OUTR

Right Headphone Output

OUTL

Left Headphone Output

BML

Left BassMax Input. Connect an external passive network between OUTL and BML to apply bass boost
to the left-channel output. See the BassMax Gain-Setting Components section. Connect BML to SGND,
if BassMax is not used.

BEEP_EN

Beep Enable Input. Connect BEEP_EN to PV

to enable the beep amplifier or to PGND to disable the

beep amplifier.

SHDN

Active-Low Shutdown Input. Drive SHDN low to disable the MAX9729. Connect SHDN to V

while B7

in command register 0x00 is equal to 1 for normal operation (see Command Registers section).

Power-Supply Input. Bypass V

to PGND with a 1µF capacitor and connect to PV

. V

and PV

are internally connected and should each have a 1µF bypass capacitor located as to close to the
device as possible.

BEEP

Beep Input

INL1

Left-Channel Input 1

INL2

Left-Channel Input 2

INL3

Left-Channel Input 3

INR1

Right-Channel Input 1

Exposed Paddle. Connect EP to SV

or leave unconnected.