Datasheet

MAX9850
Cell Phone Audio
The MAX9850 is a complete cell-phone audio playback
solution. In a typical application, ringtones are created
and output through the application’s processor on the
digital audio bus. Connect the baseband IC to the line
inputs of the MAX9850, INR and INL. The headphone
amplifier outputs a summed version of the digital audio
input and the line input (see Figure 13).
Headphone Short Circuit
The headphone amplifiers can provide almost ±300mA
per channel during a short-circuit event. The MAX9850
has been designed to withstand this current continu-
ously. To avoid unnecessarily draining a battery, it is
advised to enable the IOHR and IOHL hardware inter-
rupt. The µC can service the interrupt by disabling the
headphone amplifiers and waiting for a timeout period.
A headphone short-circuit event on the right channel
only may also indicate that a mono headphone has
been inserted into the stereo socket. The µC can then
automatically disable the right channel by placing the
MAX9850 in mono mode. This resolves a mono jack-
induced, short-circuit condition.
PC Board Layout and Bypassing
Proper layout and grounding are essential for optimum
performance. Use large traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance. Large traces also aid in moving
heat away from the package. Proper grounding improves
audio performance, minimizes crosstalk between chan-
nels, and prevents any switching noise from coupling into
the audio signal. Connect PGND, DGND, and AGND
together at a single point on the PC board. Route DGND,
PGND, and all traces that carry switching transients or
digital signals away from AGND and traces or compo-
nents in the analog audio-signal path.
Connect all components associated with the charge
pump to PGND. Connect PV
SS
and SV
SS
together at
the device. Place the charge-pump capacitors as close
to PV
SS
as possible. Ensure C2 is connected to PGND.
Bypass PV
DD
with 1µF to PGND. Place the bypass
capacitors as close to the device as possible.
The MAX9850 thin QFN package features an exposed
thermal pad on its underside. This pad lowers the pack-
age’s thermal resistance by providing a direct heat con-
duction path from the die to the printed circuit board. If
possible, connect the exposed thermal pad to an electri-
cally isolated, large pad of copper. If it cannot be left
floating, connect it to AGND.
Stereo Audio DAC with DirectDrive
Headphone Amplifier
34 ______________________________________________________________________________________
MAX9850
1μF 1μF 1μF
1.8V TO 3.6V
1μF
0.47μF
0.47μF
BASEBAND
IC
APPLICATIONS
PROCESSOR
2.2μF
REF
C1P
C1N
GPIO
HPL
HPS
HPR
PV
SS
SV
SS
PGND DGND AGND
DV
DD
PV
DD
AV
DD
LRCLK
BCLK
SDIN
MCLK
SDA
SCL
INR
INL
0.47μF
MAX9701*
3.3V TO 5.5V
0.47μF
PGNDSHDN
OUTR+
OUTR-
INL+
INL-
OUTL+
OUTL-
INR+
INR-
V
DD
0.47μF
0.47μF
0.47μF
*FUTURE PRODUCT—CONTACT FACTORY FOR AVAILABILITY.
DV
DD
10kΩ
OUTR
OUTL
Figure 13. Cell Phone Audio