Since the MAX9728A/MAX9728B do not require output-

coupling capacitors, this problem does not arise.

Additionally, the MAX9728A/MAX9728B feature exten-

sive click-and-pop suppression that eliminates any

audible transient sources internal to the device.

Typically, the output of the device driving the

MAX9728A/MAX9728B has a DC bias of half the supply

voltage. At startup, the input-coupling capacitor is

charged to the preamplifier’s DC-bias voltage through

the input and feedback resistors of the MAX9728A/

MAX9728B, resulting in a DC shift across the capacitor

and an audible click/pop. Delay the rise of SHDN 4 to 5

startup of the preamplifier, to eliminate clicks-and-pops

caused by the input filter.

Shutdown

The MAX9728A/MAX9728B feature a < 0.1µA, low-

power shutdown mode that reduces quiescent current

consumption and extends battery life for portable appli-

cations. Drive SHDN low to disable the amplifiers and

the charge pump. In shutdown mode, the amplifier out-

put impedance is set to 14k

MAX9728B). The amplifiers and charge pump are

enabled once SHDN is driven high.

Applications Information

Power Dissipation

Under normal operating conditions, linear power ampli-

fiers can dissipate a significant amount of power. The

maximum power dissipation for each package is given

in the

Absolute Maximum Ratings section under

Continuous Power Dissipation or can be calculated by

the following equation:

ture, and

°C/W as specified in the

Absolute Maximum Ratings

section. For example,

+68°C/W, and +110°C/W for the TSSOP package.

The MAX9728A/MAX9728B have two power dissipation

sources: a charge pump and the two output amplifiers.

If power dissipation for a given application exceeds the

maximum allowed for a particular package, reduce

temperature, or add heatsinking to the device. Large

output, supply, and ground traces decrease

ing more heat to be transferred from the package to the

surrounding air.

Thermal-overload protection limits total power dissipa-

tion in the MAX9728A/MAX9728B. When the junction

temperature exceeds +150°C, the thermal-protection

circuitry disables the amplifier output stage. The ampli-

fiers are enabled once the junction temperature cools

by approximately 12°C. This results in a pulsing output

under continuous thermal-overload conditions.

Output Dynamic Range

Dynamic range is the difference between the noise floor

of the system and the output level at 1% THD+N.

Determine the system’s dynamic range before setting

the maximum output gain. Output clipping occurs if the

output signal is greater than the dynamic range of the

system. The DirectDrive architecture of the MAX9728A/

MAX9728B has increased the dynamic range compared

to other single-supply amplifiers.

Maximum Output Swing

Internal device structures limit the maximum voltage

swing of the MAX9728A/MAX9728B. The output must

not be driven such that the peak output voltage exceeds

peak output swing must be less than ±4V to prevent

exceeding the absolute maximum ratings.

Component Selection

Input-Coupling Capacitor

DC bias from an incoming signal (see the

Functional

Diagram/Typical Operating Circuits). The AC-coupling

capacitor allows the device to bias the signal to an

optimum DC level. Assuming zero-source impedance,

the -3dB point of the highpass filter is given by:

device’s low-frequency response. Use capacitors

whose dielectrics have low-voltage coefficients, such

as tantalum or aluminum electrolytic. Capacitors with

high-voltage coefficients, such as ceramics, can result

in increased distortion at low frequencies.

f

RC

dB

IN IN

−

=

3

1

2

π

P

TT

DISSPKG MAX

J MAX

A

JA

()

()

=

−

θ

60mW, DirectDrive, Stereo Headphone

Amplifiers with Shutdown

8

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