max9701etgt Maxim Integrated Products, Inc., max9701etgt Datasheet - Page 14

• Manufacturer Part Number: max9701etgt
• Description: Max9701 1.3w, Filterless, Stereo Class D Audio Power Amplifier
• Manufacturer: Maxim Integrated Products, Inc.

The MAX9701 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 MAX9701 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND, and driving the other input (Figure 6).
The input amplifier can accept DC-coupled inputs that
are biased within the amplifier’s common-mode range
(see the Typical Operating Characteristics). DC cou-
pling eliminates the input-coupling capacitors, reduc-
ing component count to potentially two external
components (Figure 7). However, the highpass filtering
effect of the capacitors is lost, allowing low-frequency
signals to feed through to the load.
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
Figure 6. Single-Ended Input
14
2.5V TO 5.5V
FFM MODE WITH f
______________________________________________________________________________________
RIGHT AUDIO INPUT
0.47µF
LEFT AUDIO INPUT
10µF
SINGLE-ENDED
SINGLE-ENDED
OSC
= 1100kHz, GAIN = 6dB.
0.1µF
0.47µF
0.47µF
0.47µF
INL+
INR+
INL-
INR-
GAIN2
SHDN
V
PV
DD
DD
MAX9701
Single-Ended Input
DC-Coupled Inputs
Input Amplifier
Differential Input
OUTR+
OUTL+
OUTR-
OUTL-
GAIN1
PGND
SYNC
GND
An input capacitor, C
MAX9701 input impedance (R
that removes the DC bias from an incoming signal. The
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
interest. Use capacitors whose dielectrics have low-volt-
age coefficients, such as tantalum or aluminum electrolyt-
ic. Capacitors with high-voltage coefficients, such as
ceramics, may result in increased distortion at low fre-
quencies.
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
Figure 7. DC-Coupled Inputs
2.5V TO 5.5V
FFM MODE WITH f
CODEC BIASED TO 1/2 MAX9701 COMMON-MODE VOLTAGE.
10µF
IN
CODEC
OSC
so f
= 1100kHz, GAIN = 6dB
-3dB
0.1µF
f
−
3
is well below the lowest frequency of
dB
=
INL+
INL-
INR+
INR-
GAIN2
SHDN
V
PV
IN
DD
2π
DD
, in conjunction with the
Component Selection
R C
IN
IN IN
1
MAX9701
) forms a highpass filter
OUTL+
OUTR+
OUTR-
OUTL-
GAIN1
PGND
SYNC
GND
Input Filter