MAX9724A(2007) 查看數據表（PDF） - Maxim Integrated

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MAX9724A
(Rev.:2007)

60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown

Maxim Integrated 

60mW, DirectDrive, Stereo Headphone Amplifier

with Low RF Susceptibility and Shutdown

where TJ(MAX) is +150°C, TA is the ambient tempera-

ture, and θJA is the reciprocal of the derating factor in

°C/W as specified in the Absolute Maximum Ratings

section. For example, θJA of the thin QFN package is

+68°C/W, and 154.2°C/W for the UCSP package.

The MAX9724A/MAX9724B 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

VDD, increase load impedance, decrease the ambient

temperature, or add heatsinking to the device. Large

output, supply, and ground traces decrease θJA, allow-

ing more heat to be transferred from the package to the

surrounding air.

Thermal-overload protection limits total power dissipa-

tion in the MAX9724A/MAX9724B. 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 out-

put signal is greater than the dynamic range of the sys-

tem. The DirectDrive architecture of the MAX9724A/

MAX9724B has increased the dynamic range compared

to other single-supply amplifiers.

Maximum Output Swing

VDD < 4.35V

If the output load impedance is greater than 1kΩ, the

MAX9724A/MAX9724B can swing within a few millivolts

of their supply rail. For example, with a 3.3V supply, the

output swing is 2VRMS, or 2.83V peak while maintaining

a low 0.003% THD+N. If the supply voltage drops to

3V, the same 2.83V peak has only 0.05% THD+N.

VDD > 4.35V

Internal device structures limit the maximum voltage

swing of the MAX9724A/MAX9724B when operated at

supply voltages greater than 4.35V. The output must not

be driven such that the peak output voltage exceeds the

opposite supply voltage by 9V. For example, if VDD =

5V, the charge pump sets PVSS = -5V. Therefore, the

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

exceeding the absolute maximum ratings.

UVLO

The MAX9724A/MAX9724B feature an undervoltage

lockout (UVLO) function that prevents the device from

operating if the supply voltage is less than 2.7V. This fea-

ture ensures proper operation during brownout condi-

tions and prevents deep battery discharge. Once the

supply voltage exceeds the UVLO threshold, the

MAX9724A/MAX9724B charge pump is turned on and

the amplifiers are powered, provided that SHDN is high.

Component Selection

Input-Coupling Capacitor

The input capacitor (CIN), in conjunction with the input

resistor (RIN), forms a highpass filter that removes the

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 opti-

mum DC level. Assuming zero-source impedance, the -

3dB point of the highpass filter is given by:

f−3dB

=

1

2πRINCIN

Choose the CIN such that f-3dB is well below the lowest

frequency of interest. Setting f-3dB too high affects the

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.

Charge-Pump Capacitor Selection

Use ceramic capacitors with a low ESR for optimum

performance. For optimal performance over the extend-

ed temperature range, select capacitors with an X7R

dielectric. Table 2 lists suggested manufacturers.

Table 2. Suggested Capacitor Manufacturers

SUPPLIER

Taiyo Yuden

TDK

Murata

PHONE

800-348-2496

847-803-6100

770-436-1300

FAX

847-925-0899

847-390-4405

770-436-3030

WEBSITE

www.t-yuden.com

www.component.tdk.com

www.murata.com

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