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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

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 inverting unity-gain follower in both

devices. This results in two outputs, identical in magni-

tude, but 180° out of phase.

BIAS

The MAX4364/MAX4365 feature an internally generated

common-mode bias voltage of VCC/2 referenced to

GND. BIAS provides both click-and-pop suppression

and the DC bias level for the audio signal. BIAS is inter-

nally connected to the noninverting input of one amplifi-

er, 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

shutdown mode that reduces quiescent current con-

sumption. 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 nor-

mal operation.

Current Limit

The MAX4364/MAX4365 feature a current limit that pro-

tects the device during output short circuit and over-

load conditions. When both amplifier outputs are

shorted to either VCC or GND, the short-circuit protec-

tion is enabled 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 similar conditions. Thus, the differential gain of

+1

VOUT(P-P)

2 x VOUT(P-P)

-1

VOUT(P-P)

Figure 1. Bridge-Tied Load Configuration

the device is twice the closed-loop gain of the input

amplifier. The effective gain is given by:

AVD

=

2

×

RF

RIN

Substituting 2 ✕ VOUT(P-P) into the following equations

yields four times the output power due to doubling of

the output voltage.

VRMS

=

VOUT(P−P)

22

POUT

=

VRMS2

RL

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:

PDISSPKG(MAX)

=

TJ(MAX) − TA

θ JA

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 µMAX package is

222°C/W.

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