MAX9726 Maxim Integrated Products, MAX9726 Datasheet - Page 12

• Manufacturer Part Number: MAX9726
• Description: Headphone Amplifier
• Manufacturer: Maxim Integrated Products

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The MAX9726 includes a 64-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 [5:0].
Table 5 shows all possible attenuation settings of the
MAX9726 with respect to the overall gain set by the
external gain-setting resistors (R
uation is typically better than 120dB when driving a
32Ω load. To perform smooth-sounding volume
changes, step through all intermediate volume settings
at a rate of approximately 2ms per step when a volume
change occurs.
The MAX9726 features an I
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 MAX9726 and the
master at clock rates up to 400kHz. Figure 3 shows the
2-wire interface timing diagram. The MAX9726 is a
receive-only slave device relying on the master to gen-
erate the SCL signal. The MAX9726 cannot write to the
DirectDrive, Headphone Amplifier with
BassMax, I
Figure 3. 2-Wire Serial-Interface Timing Diagram
12
SDA
SCL
______________________________________________________________________________________
t
HD, STA
CONDITION
START
t
LOW
2
t
R
C, Volume and Gain Control
t
t
SU, DAT
HIGH
2
C-/SMBus-compatible,
IN
t
and R
F
Serial Interface
Volume Control
t
HD, DAT
F
). Mute atten-
t
SU, STA
SDA bus except to acknowledge the receipt of data
from the master. The master, typically a microcontroller,
generates SCL and initiates data transfer on the bus.
A master device communicates to the MAX9726 by
transmitting the slave address with the read/write (R/W)
bit followed by the data word. Each transmit sequence
is framed by a START (S) or REPEATED START (Sr)
condition and a STOP (P) condition. Each word trans-
mitted over the bus is 8 bits long and is always followed
by an acknowledge clock pulse.
The MAX9726 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 MAX9726 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 MAX9726 from high-
voltage spikes on the bus lines, and minimize crosstalk
and undershoot of the bus signals.
CONDITION
REPEATED
START
t
HD, STA
t
SP
t
SU, STO
CONDITION
STOP
t
BUF
CONDITION
START