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

given by the following equation:

If the power dissipation for a given application exceeds

the maximum allowed for a given package, reduce

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:

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:

The efficiency of the MAX4364/MAX4365 is:

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

Circuit/Functional Diagram) set the gain of the amplifier

as follows:

Ω.

the MAX4364/MAX4365 in a high-gain configuration

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

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

Input Filter

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:

affects the low-frequency response of the amplifier. Use

capacitors whose dielectrics have low-voltage coeffi-

ƒ=

−3

1

2

dB

IN IN

RC

π

A

R

R

VD

F

IN

=×

2

η

π

==

P

P

PR

V

OUT

IN

OUT L

CC

2

2

PV

V

R

IN

CC

PEAK

L

=









2

π

I

V

R

CC

PEAK

L

=

2

π

P

V

R

OUT

PEAK

L

=

2

2

P

V

R

DISS MAX

CC

L

2

2

2

π

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

Amplifiers with Shutdown

10

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