Datasheet

MAX9713/MAX9714
is very small. Although this movement is small, a speak-
er not designed to handle the additional power can be
damaged. For optimum results, use a speaker with a
series inductance > 30µH. Typical 8Ω speakers exhibit
series inductances in the range of 30µH to 100µH.
Optimum efficiency is achieved with speaker induc-
tances > 60µH.
Gain Selection
Table 2 shows the suggested gain settings to attain a
maximum output power from a given peak input voltage
and given load.
Internal Regulator Output (V
REG
)
The MAX9713/MAX9714 feature an internal, 6V regula-
tor output (V
REG
). The MAX9713/MAX9714 REG output
pin simplifies system design and reduces system cost
by providing a logic voltage high for the MAX9713/
MAX9714 logic pins (G_, FS_). V
REG
is not available as
a logic voltage high in shutdown mode. Do not apply
V
REG
as an input voltage high to the MAX9713/
MAX9714 SHDN pin. Do not apply V
REG
as a 6V poten-
tial to surrounding system components. Bypass REG
with a 6.3V, 0.01µF capacitor to GND.
Output Offset
Unlike a Class AB amplifier, the output offset voltage of
Class D amplifiers does not noticeably increase quies-
cent current draw when a load is applied. This is due to
the power conversion of the Class D amplifier. For
example, an 8mV DC offset across an 8Ω load results
in 1mA extra current consumption in a Class AB device.
In the Class D case, an 8mV offset into 8Ω equates
to an additional power drain of 8µW. Due to the high
efficiency of the Class D amplifier, this represents an
additional quiescent current draw of: 8µW/(V
DD
/100 ✕ η),
which is on the order of a few microamps.
Input Amplifier
Differential Input
The MAX9713/MAX9714 feature a differential input struc-
ture, making them compatible with many CODECs, and
offering improved noise immunity over a single-ended
input amplifier. In devices such as PCs, noisy digital sig-
nals can be picked up by the amplifier’s input traces.
The signals appear at the amplifiers’ inputs as common-
mode noise. A differential input amplifier amplifies the
difference of the two inputs, any signal common to both
inputs is canceled.
Single-Ended Input
The MAX9713/MAX9714 can be configured as single-
ended input amplifiers by capacitively coupling either
input to GND and driving the other input (Figure 5).
Component Selection
Input Filter
An input capacitor, C
IN
, in conjunction with the input
impedance of the MAX9713/MAX9714, forms a high-
pass 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 C
IN
so f
-3dB
is well below the lowest frequency
of interest. Setting f
-3dB
too high affects the low-fre-
quency response of the amplifier. Use capacitors
whose dielectrics 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.
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩ for opti-
mum 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.
f
RC
-
3dB
IN IN
1
2
=
π
6W, Filterless, Spread-Spectrum
Mono/Stereo Class D Amplifiers
10 ______________________________________________________________________________________
Table 2. Gain Settings
GAIN (dB)
DIFF INPUT
(V
RMS
)
R
L
(Ω)
P
OUT
at 10%
THD+N (W)
13.0 1.27 16 8
16.1 0.89 16 8
19.1 0.63 16 8
22.1 0.45 16 8
13.0 0.78 8 6
16.1 0.54 8 6
19.1 0.39 8 6
22.1 0.27 8 6
MAX9713/
MAX9714
IN+
IN-
0.47µF
0.47µF
SINGLE-ENDED
AUDIO INPUT
Figure 5. Single-Ended Input