MAX4364-MAX4365 Просмотр технического описания (PDF) - Maxim Integrated

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MAX4364-MAX4365

1.4W and 1W, Ultra-Small, Audio Power Amplifiers with Shutdown

Maxim Integrated 

1.4W and 1W, Ultra-Small, Audio Power

Amplifiers with Shutdown

The increase in power delivered by the BTL configura-

tion directly results in an increase in internal power dis-

sipation over the single-ended configuration. The

maximum power dissipation for a given VCC and load is

given by the following equation:

PDISS(MAX)

=

2VCC2

π2RL

If the power dissipation for a given application exceeds

the maximum allowed for a given package, reduce

VCC, increase load impedance, decrease the ambient

temperature or add heat sinking to the device. Large

output, supply, and ground PC board traces improve

the maximum power dissipation in the package.

Thermal-overload protection limits total power dissipa-

tion in the MAX4364/MAX4365. When the junction tem-

perature exceeds +160°C, the thermal protection

circuitry disables the amplifier output stage. The ampli-

fiers are enabled once the junction temperature cools

by 15°C. This results in a pulsing output under continu-

ous thermal overload conditions as the device heats

and cools.

The MAX4365 QFN package features an exposed ther-

mal pad on its underside. This pad lowers the thermal

resistance of the package by providing a direct heat

conduction path from the die to the PC board. Connect

the exposed thermal pad to circuit ground by using a

large pad, ground plane, or multiple vias to the ground

plane.

Efficiency

The efficiency of the MAX4364/MAX4365 is calculated

by taking the ratio of the power delivered to the load to

the power consumed from the power supply. Output

power is calculated by the following equations:

POUT

=

VPEAK2

2RL

where VPEAK is half the peak-to-peak output voltage. In

BTL amplifiers, the supply current waveform is a full-

wave rectified sinusoid with the magnitude proportional

to the peak output voltage and load. Calculate the sup-

ply current and power drawn from the power supply by

the following:

ICC

=

2VPEAK

πRL

PIN

=



VCC 

2VPEAK

πRL





The efficiency of the MAX4364/MAX4365 is:

η = POUT = π

POUTRL

2

PIN

2VCC

The device efficiency values in Table 1 are calculated

based on the previous equation and do include the

effects of quiescent current. Note that efficiency is low

at low output-power levels, but remains relatively con-

stant at normal operating, output-power levels.

Component Selection

Gain-Setting Resistors

External feedback components set the gain of both

devices. Resistors RF and RIN (see Typical Application

Circuit/Functional Diagram) set the gain of the amplifier

as follows:

AVD

=

2

×

RF

RIN

Optimum output offset is achieved when RF = 20kΩ.

Vary the gain by changing the value of RIN. When using

the MAX4364/MAX4365 in a high-gain configuration

(greater than 8V/V), a feedback capacitor may be

required to maintain stability (see Figure 2). CF and RF

limit the bandwidth of the device, preventing high-fre-

quency oscillations. Ensure that the pole created by CF

and RF is not within the frequency band of interest.

Input Filter

The input capacitor (CIN), in conjunction with RIN forms

a highpass filter that removes the DC bias from an

incoming signal. The AC-coupling capacitor allows the

amplifier to bias the signal to an optimum DC level.

Assuming zero source impedance, the -3dB point of

the highpass filter is given by:

ƒ −3dB

=

1

2πRINCIN

Choose RIN according to the Gain-Setting Resistors

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

lowest frequency of interest. Setting f-3dB too high

affects the low-frequency response of the amplifier. Use

capacitors whose dielectrics have low-voltage coeffi-

10 ______________________________________________________________________________________

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