MAX9879 datasheet(27/32 Pages) AD

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MAX9879

Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

Maxim Integrated

Read Data Format

Send the slave address with the R/W bit set to 1 to initi-

ate a read operation. The MAX9879 acknowledges

receipt of its slave address by pulling SDA low during

the 9th SCL clock pulse. A START (S) command fol-

lowed by a read command resets the address pointer

to register 0x00. The first byte transmitted from the

MAX9879 is the contents of register 0x00. Transmitted

data is valid on the rising edge of SCL. The address

pointer autoincrements after each read data byte. This

autoincrement feature allows all registers to be read

sequentially within one continuous frame. A STOP (P)

condition can be issued after any number of read data

bytes. If a STOP (P) condition is issued followed by

another read operation, the first data byte to be read

will be from register 0x00.

The address pointer can be preset to a specific register

before a read command is issued. The master presets

the address pointer by first sending the MAX9879‘s

slave address with the R/W bit set to 0 followed by the

then sent followed by the slave address with the R/W

bit set to 1. The MAX9879 then transmits the contents

of the specified register. The address pointer autoincre-

ments after transmitting the first byte. The master

acknowledges receipt of each read byte during the

acknowledge clock pulse. The master must acknowl-

edge all correctly received bytes except the last byte.

The final byte must be followed by a not acknowledge

from the master and then a STOP (P) condition. Figure

11 illustrates the frame format for reading one byte from

the MAX9879. Figure 12 illustrates the frame format for

reading multiple bytes from the MAX9879.

Applications Information

Filterless Class D Operation

Traditional Class D amplifiers require an output filter to

recover the audio signal from the amplifier’s output. The

filters add cost, increase the solution size of the amplifier,

and can decrease efficiency and THD+N performance.

The traditional PWM scheme uses large differential out-

put swings (2 x VDD(P-P)) and causes large ripple cur-

rents. Any parasitic resistance in the filter components

results in a loss of power, lowering the efficiency.

The MAX9879 does not require an output filter. The

device relies on the inherent inductance of the speaker

coil and the natural filtering of both the speaker and the

human ear to recover the audio component of the

square-wave output. Eliminating the output filter results

in a smaller, less costly, more efficient solution.

Because the frequency of the MAX9879 output is well

beyond the bandwidth of most speakers, voice coil

movement due to the square-wave frequency is very

small. Although this movement is small, a speaker not

designed to handle the additional power can be dam-

aged. For optimum results, use a speaker with a series

inductance > 10µH. Typical 8

Ω speakers exhibit series

inductances in the 20µH to 100µH range.

Component Selection

Optional Ferrite Bead Filter

In applications where speaker leads exceed 20mm,

additional EMI suppression can be achieved by using a

filter constructed from a ferrite bead and a capacitor to

ground. A ferrite bead with low DC resistance, high-

frequency (> 1.176MHz) impedance of 100

Ω to 600Ω,

and rated for at least 1A should be used. The capacitor

value varies based on the ferrite bead chosen and the

ACKNOWLEDGE FROM MAX9879

1 BYTE

AUTOINCREMENT INTERNAL

ACKNOWLEDGE FROM MAX9879

R/W

REPEATED START

SLAVE ADDRESS

DATA BYTE

Figure 12. Reading n Bytes of Indexed Data from the MAX9879

MAX9879

OUT+

OUT-

Figure 13. Optional Ferrite Bead Filter

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