MAX9737 데이터 시트보기 (PDF) - Maxim Integrated

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MAX9737

Mono 7W Class D Amplifier

Maxim Integrated 

Mono 7W Class D Amplifier

When evaluating the MAX9737 with a ferrite bead filter

and resistive load, include a series inductor (68µH for

8Ω load and 33µH for 4Ω load) to model typical loud-

speaker’s behavior. Omitting the series inductor

reduces the efficiency, the THD+N performance and

the output power of the MAX9737. When evaluating

with a loudspeaker, no series inductor is required.

Inductor-Based Output Filters

Some applications use the MAX9737 with a full induc-

tor/capacitor-based (LC) output filter. See Figure 4 for

the correct connections of these components.

The load impedance of the speaker determines the fil-

ter component selection (see Table 1).

Inductors L1 and L2 and capacitor C1 form the primary

output filter. Capacitors C2 and C3 provide common-

mode filtering to reduce radiated emissions. Capacitors

C4 and C5, plus resistors R1 and R2, form a Zobel at

the output. A Zobel corrects the output loading to com-

pensate for the rising impedance of the loudspeaker.

Without a Zobel, the filter exhibits peaking near the cut-

off frequency.

Component Selection

Gain-Setting Resistors

The output stage provides a fixed internal gain in addi-

tion to the externally set input stage gain. The fixed-out-

put stage gain is set at 13.6dB (4.8V/V). Set overall gain

by using resistors RF and RIN (Figure 5) as follows:

AV

=

-4.8

⎛

⎝⎜

RF

RIN

⎞

⎠⎟ V

/

V

where AV is the desired voltage gain. Choose RF

between 10kΩ and 50kΩ.

The PRE terminal is an operational amplifier output,

allowing the MAX9737 to be configured as a filter or an

equalizer.

Input Capacitor

An input capacitor, CIN, in conjunction with the input

resistor, RIN, of the MAX9737 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 negligible

source impedance, the -3dB point of the highpass filter

is given by:

f -3dB=

1

2πRINCIN

MAX9737

C2

L1

C1

L2

C3

Figure 4. LC Filter Configuration

C4 R1

RL

C5 R2

CIN

AUDIO

RIN

INPUT

CCOM

RF PRE

IN

COM

PC

MAX9737

OUT+

OUT-

Figure 5. Preamplifier Gain Configuration

Choose CIN such that f-3dB is well below the lowest fre-

quency of interest. To reduce low-frequency distortion,

use capacitors whose dielectrics have low-voltage

coefficients. Capacitors with high-voltage coefficients

cause increased distortion close to f-3dB. For best click-

and-pop suppression, use a 0.47µF input capacitor.

COM Capacitor

COM is the output of the internally generated DC bias

voltage. Bypass COM with a 1µF capacitor to AGND.

Regulator Capacitor

REG is the output of the internally generated DC bias

voltage. Bypass REG with a 1µF capacitor to AGND.

Power Supplies

The MAX9737 features separate supplies for signal and

power portions of the device, allowing for the optimum

combination of headroom, power dissipation and noise

immunity. The speaker amplifiers are powered from

PVDD and can range from 8V to 28V. The remainder of

the device is powered by an internal 5V regulator, VS.

Internal Regulator

The MAX9737 features an internal 5V regulator, VS,

powered from PVDD. Bypass VS with a 1µF capacitor to

AGND.

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