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MAX9760–MAX9763
Stereo 3W Audio Power Amplifiers with
Headphone Drive and Input Mux
20
______________________________________________________________________________________
Component Selection
Gain-Setting Resistors
External feedback components set the gain of the
MAX9760–MAX9763. Resistor RIN sets the gain of the
input amplifier (AVIN) and resistor RF sets the gain of
the second stage amplifier (AVOUT):
Combining AVIN and AVOUT, RIN and RF set the single-
ended gain of the device as follows:
As shown, the two-stage amplifier architecture results
in a noninverting gain configuration, preserving
absolute phase through the MAX9760–MAX9763. The
gain of the device in BTL mode is twice that of the sin-
gle-ended mode. Choose RIN between 10k
and 15k
and RF between 15k
and 100k.
Input Filter
The input capacitor (CIN), in conjunction with RIN, forms
a highpass filter that removes the DC bias from an
incoming signal. 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:
Choose RIN according to the Gain-Setting Resistors
section. Choose the CIN such that f-3dB is well below
the lowest frequency of interest. Setting f-3dB too high
affects the amplifier’s low-frequency response. Use
capacitors whose dielectrics have low-voltage coeffi-
cients, such as tantalum or aluminum electrolytic.
Capacitors with high-voltage coefficients, such as
ceramics, may result in an increased distortion at low
frequencies.
Other considerations when designing the input filter
include the constraints of the overall system,
the actual frequency band of interest, and click-and-
pop suppression.
Output-Coupling Capacitor
The MAX9760/MAX9763 require output-coupling
capacitors to operate in single-ended (headphone)
mode. The output-coupling capacitor blocks the DC
component of the amplifier output, preventing DC cur-
rent from flowing to the load. The output capacitor and
the load impedance form a highpass filter with a -3dB
point determined by:
As with the input capacitor, choose COUT such that
f-3dB is well below the lowest frequency of interest.
Setting f-3dB too high affects the amplifier‘s low-fre-
quency response.
Load impedance is a concern when choosing COUT.
Load impedance can vary, changing the -3dB point of
the output filter. A lower impedance increases the cor-
ner frequency, degrading low-frequency response.
Select COUT such that the worst-case load/COUT com-
bination yields an adequate response. Select capaci-
tors with low ESR to minimize resistive losses and
optimize power transfer to the load.
BIAS Capacitor
BIAS is the output of the internally generated 2.5VDC
bias voltage. The BIAS bypass capacitor, CBIAS,
improves PSRR and THD+N by reducing power supply
and other noise sources at the common-mode bias
node, and also generates the clickless/popless, start-
up/shutdown DC bias waveforms for the speaker ampli-
fiers. Bypass BIAS with a 1F capacitor to GND.
Supply Bypassing
Proper power-supply bypassing ensures low-noise,
low-distortion performance. Place a 0.1F ceramic
capacitor from VDD to GND. Add additional bulk
capacitance as required by the application, typically
100F. Bypass PVDD with a 100F capacitor to GND.
Locate bypass capacitors as close to the device as
possible.
Gain Select
The MAX9760–MAX9763 feature multiple gain settings
on each channel, making available different gain and
feedback configurations. The gain-setting resistor (RF)
is connected between the amplifier output (OUT_+)
and the gain setpoint (GAIN_). An internal multiplexer
switches between the different feedback resistors
f
RC
dB
L OUT
=
3
1
2
π
f
RC
dB
IN IN
=
3
1
2
π
AA
A
k
R
k
R
V
VIN
VOUT
IN
FF
IN
=×
=
×
=+
10
A
k
R
A
R
k
VIN
IN
VOUT
F
=
=
10
,