Datasheet

Linear Regulator (REG)
The supply voltage range for the MAX9709 is from 10V to
22V to achieve high-output power. An internal linear regu-
lator reduces this voltage to 6.3V for use with small-signal
and digital circuitry that does not require high-voltage sup-
ply. Bypass a 0.01µF capacitor from REG to GND.
Applications Information
Logic Inputs
All of the digital logic inputs and output have an absolute
maximum rating of +12V. If the MAX9709 is operating
with a supply voltage between 10V and 12V, digital inputs
can be connected to PV
DD
or V
DD
. If PV
DD
and V
DD
are
greater than 12V, digital inputs and outputs must be con-
nected to a digital system supply lower than 12V.
Input Amplier
Differential Input
The MAX9709 features a differential input structure, mak-
ing them compatible with many CODECs, and offering
improved noise immunity over a single-ended input ampli-
fier. In devices such as flat-panel displays, noisy digital
signals can be picked up by the amplifier’s inputs. These
signals appear at the amplifiers’ inputs as common-mode
noise. A differential input amplifier amplifies only the differ-
ence of the two inputs, while any signal common to both
inputs is attenuated.
Single-Ended Input
The MAX9709 can be configured as a single-ended input
amplifier by capacitively coupling either input to GND and
driving the other input (Figure 4).
Component Selection
Input Filter
An input capacitor, C
IN
, in conjunction with the input
impedance of the MAX9709, forms a highpass filter
that removes the DC bias from an incoming signal. The
AC-coupling capacitor allows the amplifier to bias the sig-
nal to an optimum DC level. Assuming zero-source imped-
ance, the -3dB point of the highpass filter is given by:
3dB
IN IN
1
f
2R C
=
π
Choose C
IN
so that f
-3dB
is well below the lowest fre-
quency of interest. Setting f
-3dB
too high affects the
low-frequency response of the amplifier. Use capacitors
with dielectrics that have low-voltage coefficients, such
as tantalum or aluminum electrolytic. Capacitors with
high-voltage coefficients, such as ceramics, may result in
increased distortion at low frequencies.
Output Filter
The MAX9709 does not require an output filter. However,
output filtering can be used if a design is failing radiated
emissions due to board layout or cable length, or the
circuit is near EMI-sensitive devices. See the MAX9709
evaluation kit for suggested filter topologies. The tuning
and component selection of the filter should be optimized
for the load. A purely resistive load (8Ω) used for lab test-
ing requires different components than a real, complex
load-speaker load.
Charge-Pump Capacitor Selection
The MAX9709 has an internal charge-pump converter
that produces a voltage level for internal circuitry. It
requires a flying capacitor (C1) and a holding capacitor
(C2). Use capacitors with an ESR less than 100mΩ for
optimum performance. Low-ESR ceramic capacitors mini-
mize the output resistance of the charge pump. For best
performance over the extended temperature range, select
capacitors with an X7R dielectric. The capacitors’ voltage
rating must be greater than 36V.
Figure 4. Single-Ended Input Connections
INR+
INR-
MAX9709
1µF
1µF
MAX9709 25W/50W, Filterless, Spread-Spectrum,
Stereo/Mono, Class D Amplier
www.maximintegrated.com
Maxim Integrated
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