Detailed Description

The MAX4364/MAX4365 bridged audio power ampli-

fiers can deliver 1.4W into 8Ω (MAX4364) or 1W into

8Ω (MAX4365) while operating from a single 5V supply.

These devices consist of two high-output-current op amps

configured as a bridge-tied load (BTL) amplifier (see

Typical Application Circuit/Functional Diagram). The gain

of the device is set by the closed-loop gain of the input op

amp. The output of the first amplifier serves as the input

to the second amplifier, which is configured as an invert-

ing unity-gain follower in both devices. This results in two

outputs, identical in magnitude, but 180° out of phase.

BIAS

The MAX4364/MAX4365 feature an internally generated

BIAS provides both click-and-pop suppression and the DC

bias level for the audio signal. BIAS is internally connected

to the noninverting input of one amplifier, and should be

connected to the noninverting input of the other amplifier

for proper signal biasing (see Typical Application Circuit/

Functional Diagram). Choose the value of the bypass

capacitor as described in the BIAS Capacitor section.

Shutdown

The MAX4364/MAX4365 feature a 10nA, low-power shut-

down mode that reduces quiescent current consumption.

Pulling SHDN high disables the device’s bias circuitry, the

amplifier outputs go high impedance, and BIAS is driven

to GND. Connect SHDN to GND for normal operation.

Current Limit

The MAX4364/MAX4365 feature a current limit that pro-

tects the device during output short circuit and overload

conditions. When both amplifier outputs are shorted to

and the amplifier enters a pulsing mode, reducing the

average output current to a safe level. The amplifier

remains in this mode until the overload or short-circuit

condition is removed.

Applications Information

Bridge-Tied Load

The MAX4364/MAX4365 are designed to drive a load

differentially in a BTL configuration. The BTL configura-

tion (Figure 1) offers advantages over the single-ended

configuration, where one side of the load is connected to

ground. Driving the load differentially doubles the output

voltage compared to a single-ended amplifier under simi-

lar conditions. Thus, the differential gain of the device is

twice the closed-loop gain of the input amplifier. The effec-

tive gain is given by:

VD

IN

R

A2

R

yields four times the output power due to doubling of the

output voltage.

O UT(P P )

RM S

2

RM S

O UT

L

V

V

22

V

P

R

−

=

=

Since the differential outputs are biased at midsupply,

there is no net DC voltage across the load. This elimi-

nates the need for DC-blocking capacitors required for

single-ended amplifiers. These capacitors can be large,

expensive, consume board space, and degrade low-

frequency performance.

Power Dissipation

Under normal operating conditions, the MAX4364/

MAX4365 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:

J(M AX )

A

DISSPKG(M AX )

JA

TT

P

−

=

θ

specified in the Package Thermal Characteristics section.

Figure 1. Bridge-Tied Load Configuration

+1

-1

MAX4364/MAX4365

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

Amplifiers with Shutdown

www.maximintegrated.com

Maxim Integrated │ 9