MAX4409 Maxim Integrated Products, MAX4409 Datasheet - Page 9

• Manufacturer Part Number: MAX4409
• Description: Stereo Headphone Amplifier
• Manufacturer: Maxim Integrated Products

The MAX4409 stereo headphone driver features Maxim’s
patented DirectDrive architecture, eliminating the large
output-coupling capacitors required by traditional single-
supply headphone drivers. The device consists of two
80mW Class AB headphone drivers, undervoltage lock-
out (UVLO)/shutdown control, charge-pump, and com-
prehensive click-and-pop suppression circuitry (see
Typical Application Circuit). The charge pump inverts the
positive supply (PV
(PV
lar supplies with their outputs biased about GND (Figure
1). The drivers have almost twice the supply range com-
pared to other 3V single-supply drivers, increasing the
available output power. The benefit of this GND bias is
that the driver outputs do not have a DC component typi-
cally V
unnecessary, improving frequency response while con-
serving board space and system cost.
The MAX4409 also features a common-mode voltage
sense input that corrects for mismatch between the
SGND of the device and the potential at the headphone
jack return. A low-power shutdown mode reduces sup-
ply current to 6µA. The device features an undervoltage
lockout that prevents operation from an insufficient
power supply and click-and-pop suppression that elim-
inates audible transients on startup and shutdown.
Additionally, the MAX4409 features thermal overload
and short-circuit protection and can withstand ±8kV
ESD strikes on the output pins.
When the headphone jack is used as a line out to inter-
face between other equipment (notebooks, desktops,
and stereo receivers), potential differences between
the equipment grounds can create ground loops and
excessive ground current flow. The MAX4409 COM
input senses and corrects for the difference between
the headphone return and device ground. Connect
COM through a resistive voltage-divider between the
headphone jack return and SGND of the device (see
Typical Application Circuit). For optimum common-
mode rejection, use the same value resistors for R1 and
R
capacitor in between with SGND and R2 (see Typical
Application Circuit). If ground sensing is not required,
connect COM directly to SGND through a 5kΩ resistor.
Traditional single-supply headphone drivers have their
outputs biased about a nominal DC voltage (typically
half the supply) for maximum dynamic range. Large
coupling capacitors are needed to block this DC bias
IN
SS
, and R2 and R
). The headphone drivers operate from these bipo-
DD
/2. Thus, the large DC-blocking capacitors are
_______________________________________________________________________________________
F
. Improve DC CMRR by adding a
DD
Detailed Description
80mW, DirectDrive, Stereo Headphone
), creating a negative supply
Common-Mode Sense
Amplifier with Common-Mode Sense
DirectDrive
from the headphone. Without these capacitors, a signif-
icant amount of DC current flows to the headphone,
resulting in unnecessary power dissipation and possi-
ble damage to both headphone and headphone driver.
Maxim’s patented DirectDrive architecture uses a
charge pump to create an internal negative supply volt-
age. This allows the outputs of the MAX4409 to be
biased about GND, almost doubling dynamic range
while operating from a single supply. With no DC com-
ponent, there is no need for the large DC-blocking
capacitors. Instead of two large (220µF, typ) tantalum
capacitors, the MAX4409 charge pump requires two
small ceramic capacitors, thereby conserving board
space, reducing cost, and improving the frequency
response of the headphone driver. See the Output
Power vs. Charge-Pump Capacitance and Load
Resistance graph in the Typical Operating Char-
acteristics for details of the possible capacitor sizes.
There is a low DC voltage on the driver outputs due to
amplifier offset. However, the offset of the MAX4409 is
Figure 1. Traditional Driver Output Waveform vs. MAX4409
Output Waveform
V
V
OUT
OUT
CONVENTIONAL DRIVER-BIASING SCHEME
DirectDrive BIASING SCHEME
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V
GND
GND
V
+V
-V
DD
DD
DD
DD
/2
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