max9773etgt Maxim Integrated Products, Inc., max9773etgt Datasheet - Page 15

• Manufacturer Part Number: max9773etgt
• Description: Max9773 1.8w, Filterless, Ultra-low Emi, Stereo Class D Audio Power Amplifier
• Manufacturer: Maxim Integrated Products, Inc.

The internal input resistance, R
gain setting. The R1 resistors attenuate the gain and
resistors R2 compensate for R
be as high as 25%. C
sate for the total change in input impedance or the low-
frequency roll-off point shifts.
The MAX9773 features a differential input structure,
making it compatible with many CODECs and offers
improved noise immunity over a single-ended input
amplifier. In devices such as cellular phones, high-fre-
quency signals from the RF transmitter can be picked
up by the amplifier’s input traces. The signals appear at
the amplifier’s inputs as common-mode noise. A differ-
ential input amplifier amplifies the difference of the two
inputs, any signal common to both inputs is canceled.
The MAX9773 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND, and driving the other input (Figure 7).
An input capacitor, C
MAX9773 input impedance (R
that removes the DC bias from an incoming signal. The
Figure 6. Custom Gain Setting
C
C
C
C
IN
IN
IN
IN
R1
R1
R1
R1
______________________________________________________________________________________
R2
R2
IN
Stereo Class D Audio Power Amplifier
IN
must be adjusted to compen-
INL+
INL-
INR+
INR-
, in conjunction with the
Component Selection
IN
IN
R
R
R
R
IN
IN
IN
IN
) forms a highpass filter
IN
’s tolerance, which can
MAX9773
, changes with each
Single-Ended Input
Input Amplifier
Differential Input
1.8W, Filterless, Ultra-Low EMI,
Input Filter
AC-coupling capacitor allows the amplifier to automati-
cally bias the signal to an optimum DC level. Assuming
zero-source impedance, the -3dB point of the highpass
filter is given by:
Choose C
of interest. 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.
Other considerations when designing the input filter
include the constraints of the overall system and the
actual frequency band of interest. Although high-fidelity
audio calls for a flat-gain response between 20Hz and
20kHz, portable voice-reproduction devices such as
cellular phones and two-way radios need only concen-
trate on the frequency range of the spoken human voice
(typically 300Hz to 3.5kHz). In addition, speakers used
in portable devices typically have a poor response
below 300Hz. Taking these two factors into considera-
tion, the input filter may not need to be designed for a
20Hz to 20kHz response, saving both board space and
cost due to the use of smaller capacitors.
Figure 7. Single-Ended Input
2.5V TO 5.5V
FFM MODE WITH f
RIGHT AUDIO INPUT
0.47µF
LEFT AUDIO INPUT
10µF
SINGLE-ENDED
SINGLE-ENDED
IN
so f
OSC
0.1µF
= 1100kHz, GAIN = 15.6dB.
-3dB
f
−
3
0.47µF
0.47µF
0.47µF
dB
is well below the lowest frequency
=
INL+
INR+
INL-
INR-
GAIN2
SHDN
V
PV
2π
DD
DD
R C
IN IN
1
MAX9773
OUTR+
OUTL+
OUTL-
OUTR-
GAIN1
PGND
SYNC
GND
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