MAX9723BEBE+T Datasheet MAX9723DEBE+T, MAX9723DETE+T, MAX9723DETE+ | P10-P12

MAX9723

the headphone. The MAX9723A and MAX9723B have a

maximum amplifier gain of 0dB while the MAX9723C

and MAX9723D have a maximum gain of +6dB.

Amplifier volume is digitally programmable to any one

of 32 levels.

DirectDrive

Traditional single-supply headphone amplifiers have

their outputs biased at a nominal DC voltage, typically

half the supply, for maximum dynamic range. Large cou-

pling capacitors are needed to block this DC bias from

the headphone. Without these capacitors, a significant

amount of DC current flows to the headphone, resulting

in unnecessary power dissipation and possible damage

to both headphone and headphone amplifier.

Maxim’s DirectDrive architecture uses a charge pump to

create an internal negative supply voltage. This allows

the MAX9723 headphone amplifier outputs to be biased

at 0V, almost doubling the dynamic range while operat-

ing from a single supply. With no DC component, there is

no need for the large DC-blocking capacitors. Instead of

two large (typically 220µF) tantalum capacitors, the

MAX9723 charge pump requires only two small 1µF

ceramic capacitors, thereby conserving board space,

reducing cost, and improving the low-frequency

response of the headphone amplifier. See the Output

Power vs. Charge-Pump Capacitance and Load

Resistance graph in the Typical Operating Characteris-

tics for details of the possible capacitor sizes.

In addition to the cost and size disadvantages, the DC-

blocking capacitors required by conventional head-

phone amplifiers limit low-frequency response and can

distort the audio signal.

Previous attempts at eliminating the output-coupling

capacitors involved biasing the headphone return

(sleeve) to the DC bias voltage of the headphone

amplifiers. This method raises some issues:

1) The sleeve is typically grounded to the chassis.

Using the midrail biasing approach, the sleeve must

be isolated from system ground, complicating prod-

uct design. The DirectDrive output biasing scheme

allows the sleeve to be grounded.

2) During an ESD strike, the amplifier’s ESD structure is

the only path to system ground. The amplifier must

be able to withstand the full ESD strike. The

MAX9723 headphone outputs can withstand an

±8kV ESD strike (HBM).

3) When using the headphone jack as a line out to

other equipment, the bias voltage on the sleeve may

conflict with the ground potential from other equip-

ment, resulting in possible damage to the amplifiers.

The DirectDrive outputs of the MAX9723 can be

directly coupled to other ground-biased equipment.

Charge Pump

The MAX9723 features a low-noise charge pump. The

600kHz switching frequency is well beyond the audio

range, and does not interfere with the audio signals.

This enables the MAX9723 to achieve a 99dB SNR. The

switch drivers feature a controlled switching speed that

minimizes noise generated by turn-on and turn-off tran-

sients. Limiting the switching speed of the charge

pump minimizes di/dt noise caused by the parasitic

bond wire and trace inductance. Although not typically

required, additional high-frequency noise attenuation

can be achieved by increasing the size of C2 (see the

Functional Diagram/Typical Operating Circuit).

Shutdown

The MAX9723 features a 5µA, low-power shutdown

mode that reduces quiescent current consumption and

extends battery life. Shutdown is controlled by a hard-

ware or software interface. Driving SHDN low disables

the drive amplifiers, bias circuitry, charge pump, and

sets the headphone amplifier output impedance to

20kΩ. Similarly, the MAX9723 enters shutdown when bit

seven (B7) in the control register is reset. SHDN and B7

must be high to enable the MAX9723. The I

C interface

is active and the contents of the command register are

not affected when in shutdown. This allows the master

to write to the MAX9723 while in shutdown.

Stereo DirectDrive Headphone Amplifier

with BassMax, Volume Control, and I

10 ______________________________________________________________________________________

-V

GND

SGND

CONVENTIONAL AMPLIFIER BIASING SCHEME

DirectDrive BIASING SCHEME

Figure 1. Traditional Amplifier Output vs. MAX9723 DirectDrive

Output

Click-and-Pop Suppression

The output-coupling capacitor is a major contributor of

audible clicks and pops in conventional single-supply

headphone amplifiers. The amplifier charges the cou-

pling capacitor to its output bias voltage at startup.

During shutdown the capacitor is discharged. This

charging and discharging results in a DC shift across

the capacitor, which appears as an audible transient at

the speaker. Since the MAX9723 headphone amplifier

does not require output-coupling capacitors, no audi-

ble transients occur.

Additionally, the MAX9723 features extensive click-and-

pop suppression that eliminates any audible transient

sources internal to the device. The Power-Up/Power-

Down Waveform in the Typical Operating Characteristics

shows that there are minimal transients at the output upon

startup or shutdown.

In most applications, the preamplifier driving the

MAX9723 has a DC bias of typically half the supply.

The input-coupling capacitor is charged to the pream-

plifier’s bias voltage through the MAX9723’s input

impedance (R

) during startup. The resulting voltage

shift across the capacitor creates an audible click/pop.

To avoid clicks/pops caused by the input filter, delay

the rise of SHDN by at least 4 time constants, 4 x R

, relative to the start of the preamplifier.

BassMax (Bass Boost)

Typical headphones do not have a flat-frequency

response. The small physical size of the diaphragm

does not allow the headphone speaker to efficiently

reproduce low frequencies. This physical limitation

results in attenuated bass response. The MAX9723

includes a bass boost feature that compensates for the

headphone’s poor bass response by increasing the

amplifier gain at low frequencies.

The DirectDrive output of the MAX9723 has more head-

room than typical single-supply headphone amplifiers.

This additional headroom allows boosting the bass fre-

quencies without the output-signal clipping.

Program the BassMax gain and cutoff frequency with

external components connected between OUT_ and

BB_ (see the Functional Diagram/Typical Operating

Circuit). Use the I

C-compatible interface to program the

command register to enable/disable the BassMax circuit.

BB_ is connected to the noninverting input of the output

amplifier when BassMax is enabled. BB_ is pulled to

SGND when BassMax is disabled. The typical application

of the BassMax circuit involves feeding a lowpass version

of the output signal back to the amplifier. This is realized

using positive feedback from OUT_ to BB_. Figure 2

shows the connections needed to implement BassMax.

Maximum Gain Control

The MAX9723A and MAX9723B have selectable

maximum gains of -5dB or 0dB (see Table 5) while

the MAX9723C and MAX9723D have selectable maxi-

mum gains of +1dB or +6dB (see Table 6). Bit 5 in the

command register selects between the two maximum

gain settings.

Volume Control

The MAX9723 includes a 32-level volume control that

adjusts the gain of the output amplifiers according to

the code contained in the command register. Volume is

programmed through the command register bits [4:0].

Tables 7–10 show all of the available gain settings for

the MAX9723A–MAX9723D. The mute attenuation is

typically better than 100dB when driving a 32Ω load.

Serial Interface

The MAX9723 features an I

C/SMBus-compatible,

2-wire serial interface consisting of a serial data line

(SDA) and a serial clock line (SCL). SDA and SCL facili-

tate communication between the MAX9723 and the

master at clock rates up to 400kHz. Figure 3 shows the

2-wire interface timing diagram. The MAX9723 is a

receive-only slave device relying on the master to gen-

erate the SCL signal. The MAX9723 cannot write to the

SDA bus except to acknowledge the receipt of data

MAX9723

Stereo DirectDrive Headphone Amplifier

with BassMax, Volume Control, and I

______________________________________________________________________________________ 11

OUT_

BB_

AUDIO

INPUT

MAX9723

BassMax

ENABLE

Figure 2. BassMax External Connections

MAX9723

from the master. The master, typically a microcontroller,

generates SCL and initiates data transfer on the bus.

A master device communicates to the MAX9723 by

transmitting the proper address followed by the data

word. Each transmit sequence is framed by a START (S)

or REPEATED START (Sr) condition and a STOP (P) con-

dition. Each word transmitted over the bus is 8 bits long

and is always followed by an acknowledge clock pulse.

The MAX9723 SDA line operates as both an input and

an open-drain output. A pullup resistor, greater than

500Ω, is required on the SDA bus. The MAX9723 SCL

line operates as an input only. A pullup resistor, greater

than 500Ω, is required on SCL if there are multiple mas-

ters on the bus, or if the master in a single-master sys-

tem has an open-drain SCL output. Series resistors in

line with SDA and SCL are optional. Series resistors

protect the digital inputs of the MAX9723 from high-

voltage spikes on the bus lines, and minimize crosstalk

and undershoot of the bus signals.

Bit Transfer

One data bit is transferred during each SCL cycle. The

data on SDA must remain stable during the high period

of the SCL pulse. Changes in SDA while SCL is high

are control signals (see the START and STOP

Conditions section). SDA and SCL idle high when the

C bus is not busy.

Start and Stop Conditions

SDA and SCL idle high when the bus is not in use. A

master device initiates communication by issuing a

START condition. A START condition is a high-to-low

transition on SDA with SCL high. A STOP condition is a

low-to-high transition on SDA while SCL is high (Figure

4). A START condition from the master signals the begin-

ning of transmission to the MAX9723. The master termi-

nates transmission and frees the bus by issuing a STOP

condition. The bus remains active if a REPEATED START

condition is generated instead of a STOP condition.

Early STOP Conditions

The MAX9723 recognizes a STOP condition at any point

during data transmission except if the STOP condition

occurs in the same high pulse as a START condition.

Slave Address

The MAX9723 is available with one of two preset slave

addresses (see Table 1). The address is defined as the

seven most significant bits (MSBs) followed by the

Read/Write (R/W) bit. The address is the first byte of

information sent to the MAX9723 after the START condi-

tion. The MAX9723 is a slave device only capable of

being written to. The sent R/W bit must always be a

zero when configuring the MAX9723.

The MAX9723 acknowledges the receipt of its address

even if R/W is set to 1. However, the MAX9723 will not

drive SDA. Addressing the MAX9723 with R/W set to 1

causes the master to receive all 1’s regardless of the

contents of the command register.

Acknowledge

The acknowledge bit (ACK) is a clocked 9th bit that the

MAX9723 uses to handshake receipt of each byte of

Stereo DirectDrive Headphone Amplifier

with BassMax, Volume Control, and I

12 ______________________________________________________________________________________

SCL

SDA

START

CONDITION

STOP

CONDITION

REPEATED

START

CONDITION

START

CONDITION

HD, STA

SU, STA

HD, STA

BUF

SU, STO

LOW

SU, DAT

HD, DAT

HIGH

Figure 3. 2-Wire Serial-Interface Timing Diagram

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P25

MAX9723BEBE+T

Mfr. #:

Buy MAX9723BEBE+T

Manufacturer:

Maxim Integrated

Description:

Audio Amplifiers Stereo DirectDrive Headphone Amplifier

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MAX9723BEBE+T

MAX9723BEBE+T

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