MAX9725 Maxim Integrated Products, MAX9725 Datasheet - Page 8

• Manufacturer Part Number: MAX9725
• Description: Stereo Headphone Amplifier
• Manufacturer: Maxim Integrated Products

frequency noise attenuation can be achieved by
increasing the size of C2 (see the Functional Diagram).
Extra noise attenuation is not typically required.
The MAX9725’s low-power shutdown mode reduces
supply current to 0.6µA. Driving SHDN low disables the
amplifiers and charge pump. The driver’s output imped-
ance is typically 50kΩ (MAX9725A), 37.5kΩ (MAX9725B),
25kΩ (MAX9725), or 100kΩ (MAX9725D) when in shut-
down mode.
In conventional single-supply audio drivers, the output-
coupling capacitor is a major contributor of audible
clicks and pops. Upon startup, the driver charges the
coupling capacitor to its bias voltage, typically half the
supply. Likewise, on shutdown, the capacitor is dis-
charged to GND. This results in a DC shift across the
capacitor that appears as an audible transient at the
speaker. The MAX9725’s DirectDrive technology elimi-
nates the need for output-coupling capacitors.
The MAX9725 also features extensive click-and-pop
suppression that eliminates any audible transient
sources internal to the device. The Power-Up/Down
Waveform in the Typical Operating Characteristics
shows minimal DC shift and no spurious transients at
the output upon startup or shutdown.
In most applications, the output of the preamplifier dri-
ving the MAX9725 has a DC bias of typically half the
supply. At startup, the input-coupling capacitor is
charged to the preamplifier’s DC bias voltage through
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
Figure 2. Low-Frequency Attenuation for Common DC-Blocking
Capacitor Values
8
_______________________________________________________________________________________
-10
-15
-20
-25
-30
-35
-3
-5
0
10
330µF
LF ROLLOFF (16Ω LOAD)
220µF
100µF
Click-and-Pop Suppression
33µF
FREQUENCY (Hz)
100
-3dB CORNER FOR
100µF IS 100Hz
1k
Shutdown
the internal input resistor (25kΩ, typ) causing an audi-
ble click and pop. Delaying the rise of SHDN 4 or 5
time constants, based on R
up of the preamplifier eliminates any click and pop
caused by the input filter (see the Functional Diagram).
Linear power amplifiers can dissipate a significant
amount of power under normal operating conditions.
The maximum power dissipation for each package is
given in the Absolute Maximum Ratings section under
Continuous Power Dissipation or can be calculated by
the following equation:
where T
ture, and θ
°C/W as specified in the Absolute Maximum Ratings
section. For example, θ
+59.3°C/W.
The MAX9725 has two power dissipation sources, the
charge pump and the two amplifiers. If the power dissi-
pation exceeds the rated package dissipation, reduce
V
temperature, or add heatsinking to the device. Large
output, supply, and ground traces decrease θ
ing more heat to be transferred from the package to
surrounding air.
Figure 3. Distortion Contributed By DC-Blocking Capacitors
DD
, increase load impedance, decrease the ambient
J(MAX)
0.0001
0.001
P
0.01
0.1
DISSPKG(MAX)
JA
10
1
10
is the reciprocal of the derating factor in
is +150°C, T
Applications Information
TO DC-BLOCKING CAPACITORS
ALUM/ELEC
ADDITIONAL THD+N DUE
100
FREQUENCY (Hz)
JA
TANTALUM
=
for the thin QFN package is
IN
1k
T
A
J(MAX)
x C
is the ambient tempera-
Power Dissipation
θ
IN
JA
10k
, relative to the start-
- T
A
100k
JA
, allow-