MAX9715 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX9715

2.8W, Low-EMI, Stereo, Filterless Class D Audio Amplifier

Maxim Integrated 

2.8W, Low-EMI, Stereo, Filterless Class D

Audio Amplifier

Voice coil movement due to the square-wave frequency

is very small because the switching frequency of the

MAX9715 is well beyond the bandwidth of most speak-

ers. Although this movement is small, a speaker not

designed to handle the additional power may be

damaged. Use a speaker with a series inductance

> 30μH for optimum efficiency. Typical 8Ω speakers

exhibit series inductances in the 30μH to 100μH range.

The highest efficiency is achieved with speaker induc-

tances > 60μH.

Component Selection

Input Filter

The input capacitor (CIN), in conjunction with the amplifier

input resistance (RIN), forms a highpass filter that

removes the DC bias from an incoming signal (see the

Typical Application Circuit). 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:

f−3dB

=

2π

×

1

RIN

×

CIN

RIN is the amplifier’s internal input resistance value given

in the Electrical Characteristics table. Choose CIN so

f-3dB is well below the lowest frequency of interest.

Setting f-3dB too high affects the amplifier’s low-frequency

response. Use capacitors with low-voltage coefficient

dielectrics, such as tantalum or aluminum electrolytic.

Capacitors with high-voltage coefficients, such as ceram-

ics, may result in increased distortion at low frequencies.

The inability of small diaphragm speakers to reproduce

low frequencies can be exploited to improve click-and-

pop performance. Set the cutoff frequency of the

MAX9715’s input highpass filter to match the speaker’s

frequency response. Doing so will allow for smaller CIN

values and reduce click-and-pop.

Output Filter

The MAX9715 speaker amplifiers do not require output

filters. However, output filtering can be used if a design

is failing radiated emissions due to board layout, cable

length, or the circuit is near EMI-sensitive devices. Use

a ferrite bead filter or a common-mode choke when radi-

ated frequencies above 10MHz are of concern. Use an

LC filter when radiated frequencies below 10MHz are of

concern, or when long cables (>75mm) connect the

amplifier to the speaker. Figure 4 shows possible output

filter connections.

OUTL+

OUTL-

MAX9715

OUTR+

OUTR-

OUTL+

OUTL-

MAX9715

OUTR+

OUTR-

OUTL+

OUTL-

MAX9715

OUTR+

OUTR-

(a)

TYPICAL APPLICATION

<75mm OF SPEAKER CABLE.

(b)

COMMON-MODE CHOKE FOR

APPLICATIONS USING CABLE LENGTHS

GREATER THAN 150mm.

Figure 4. Optional Speaker Amplifier Output Filter—Guidelines for FCC Compliance

(c)

LC FILTER WHEN USING LONG CABLE

LENGTHS OR IN APPLICATIONS

THAT ARE SENSITIVE TO EMI.

_______________________________________________________________________________________ 9

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