max9752aetit Maxim Integrated Products, Inc., max9752aetit Datasheet - Page 22

• Manufacturer Part Number: max9752aetit
• Description: 2.2w, Low-emi, Stereo, Class D Power Amplifiers With Directdrive Headphone Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

The MAX9752/MAX9753/MAX9754 have different sup-
plies for each portion of the device allowing for the opti-
mum combination of headroom, power dissipation, and
noise immunity. The speaker amplifiers are powered from
PV
amplifiers are powered from HPV
the positive supply of the headphone amplifiers and
ranges from 3V to 5.5V. V
for the headphone amplifiers. Connect V
charge pump is powered by CPV
3V to 5.5V. CPV
HPV
and the resulting voltage appears at CPV
der of the device is powered by V
The input capacitor (C
fier input resistance (R
removes the DC bias from an incoming signal (see the
Functional Diagrams). The AC-coupling capacitor
allows the amplifier to bias the signal to an optimum DC
level. Assuming zero source impedance, the -3dB point
of the highpass filter is given by:
R
in the Electrical Characteristics table. Choose C
f
Setting f
response. Use capacitors with low-voltage coefficient
dielectrics, such as tantalum or aluminum electrolytic.
Capacitors with high-voltage coefficients, such as ceram-
ics, may result in increased distortion at low frequencies.
In most applications, the low-EMI, Class D outputs do not
require output filters. The device passes FCC emissions
standards with 76mm of unshielded speaker cables.
Output filtering can be used if lower EMI is desired. Use a
ferrite bead filter when radiated frequencies above
10MHz are of concern. Use an LC filter when radiated fre-
quencies below 10MHz are of concern, or when long
leads (> 76mm) connect the amplifier to the speaker.
BIAS is the output of the internally generated DC bias
voltage. The BIAS bypass capacitor, C
PSRR and THD+N by reducing power supply and other
noise sources at the common-mode bias node, and
also generates the clickless/popless, startup/shutdown,
DC bias waveforms for the speaker amplifiers. Bypass
BIAS with a 1µF capacitor to GND.
2.2W, Low-EMI, Stereo, Class D Power Amplifiers
with DirectDrive Headphone Amplifiers
22
-3dB
IN
DD
is the amplifier’s internal input resistance value given
DD
______________________________________________________________________________________
. PV
is well below the lowest frequency of interest.
. The charge pump inverts the voltage at CPV
-3dB
DD
too high affects the amplifier’s low-frequency
ranges from 4.5V to 5.5V. The headphone
DD
f
−
3
dB
should be the same potential as
IN
IN
), in conjunction with the ampli-
=
SS
), forms a highpass filter that
2 π
Component Selection
is the negative supply input
Optional Output Filtering
R C
IN IN
1
DD
DD
DD
.
Power Supplies
, which ranges from
and V
SS
BIAS Capacitor
SS
Input Filtering
BIAS
to CPV
SS
. The remain-
. HPV
, improves
SS
IN
DD
. The
DD
so
is
,
Use capacitors with less than 100mΩ of equivalent
series resistance (ESR). Low-ESR ceramic capacitors
minimize the output impedance of the charge pump.
Capacitors with an X7R dielectric provide the best per-
formance over the extended temperature range.
The value of the flying capacitor (C1) affects the load
regulation and output resistance of the charge pump.
Choosing C1 too small degrades the ability to provide
sufficient current drive, which leads to a loss of output
voltage. Increasing the value of C1 improves load regu-
lation and reduces the charge-pump output resistance.
See the Output Power vs. Charge-Pump Capacitance
and Load Resistance graph in the Typical Operating
Characteristics. Above 2.2µF, the on-resistance of the
switches and the ESR of C1 and C2 dominate. The rec-
ommended range of capacitors is from 0.33µF to 3.3µF.
The output capacitor value and ESR directly affect the
ripple at CPV
output ripple. Decreasing the ESR of C2 reduces both
ripple and output resistance. Lower capacitance values
can be used in systems with low, maximum output
power levels. See the Output Power vs. Charge-Pump
Capacitance and Load Resistance graph in the Typical
Operating Characteristics. C2 must be greater than or
equal to C1. The recommended range of capacitors is
from 0.33µF to 3.3µF.
The CPV
impedance of the power supply and reduces the
impact of the charge-pump switching transients on the
headphone driver outputs. Bypass CPV
same value as C1, and place it physically close to
CPV
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 mov-
ing heat away from the package. Proper grounding
improves audio performance, minimizes crosstalk
between channels, and prevents any switching noise
from coupling into the audio signal. Connect CPGND,
PGND, and GND together at a single point on the PC
board. Route CPGND, PGND, and all traces that carry
switching transients away from GND and the traces and
components in the audio signal path.
DD
and PGND.
DD
Charge-Pump Capacitor Selection
bypass capacitor (C3) lowers the output
SS
. Increasing the value of C2 reduces
Layout and Grounding
CPV
Output Capacitor (C2)
Flying Capacitor (C1)
DD
Bypass Capacitor
DD
with C3, the