MAX9820 データシートの表示（PDF） - Maxim Integrated

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MAX9820

DirectDrive Headphone Amplifier with External Gain

Maxim Integrated 

DirectDrive Headphone Amplifier

with External Gain

Shutdown

The MAX9820 features a low-power shutdown mode

that reduces quiescent current consumption to less

than 1µA, extending battery life for portable applica-

tions. Drive SHDN low to disable the amplifiers and the

charge pump. In shutdown mode, the amplifier output

impedance is set to 600Ω || RFB. 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 or can be cal-

culated by the following equation:

PDISSPKG(MAX)

=

TJ(MAX) −

θJA

TA

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.

The MAX9820 has two power dissipation sources: a

charge pump and the two output amplifiers. If power

dissipation for a given application exceeds the maxi-

mum allowed package power dissipation, reduce VDD,

increase load impedance, decrease the ambient tem-

perature, or add heatsinking to the device. Large out-

put, supply, and ground traces decrease θJA, allowing

more heat to be transferred from the package to the

surrounding air.

Thermal-overload protection limits total power dissipa-

tion in the MAX9820. When the junction temperature

exceeds 145°C (typ), the thermal protection circuitry

disables the amplifier output stage. The amplifiers are

enabled once the junction temperature cools by

approximately 15°C.

Undervoltage Lockout (UVLO)

The MAX9820 features a UVLO function that prevents

the device from operating if the supply voltage falls

below 2.2V (min). This feature ensures proper operation

during brownout conditions and prevents deep battery

discharge. Once the supply voltage reaches the mini-

mum supply voltage range, the MAX9820 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 Circuit). 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 or

X5R dielectric. Table 2 lists suggested manufacturers.

Table 2. Suggested Capacitor Vendors

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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