MAX9714 Maxim Integrated Products, Inc., MAX9714 Datasheet - Page 8

• Manufacturer Part Number: MAX9714
• Description: 6w, Filterless, Spread-spectrum Mono/stereo Class D Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

6W, Filterless, Spread-Spectrum
Mono/Stereo Class D Amplifiers
Figure 1. MAX9714 Outputs with No Input Signal Applied
8
The MAX9713/MAX9714 filterless, Class D audio power
amplifiers feature several improvements to switch-
mode amplifier technology. The MAX9713 is a mono
amplifier, the MAX9714 is a stereo amplifier. These
devices offer Class AB performance with Class D effi-
ciency, while occupying minimal board space. A
unique filterless modulation scheme and spread-spec-
trum switching mode create a compact, flexible, low-
noise, efficient audio power amplifier. The differential
input architecture reduces common-mode noise pick-
up, and can be used without input-coupling capacitors.
The devices can also be configured as a single-ended
input amplifier.
Comparators monitor the device inputs and compare
the complementary input voltages to the triangle wave-
form. The comparators trip when the input magnitude of
the triangle exceeds their corresponding input voltage.
The MAX9713/MAX9714 feature three FFM modes with
different switching frequencies (Table 1). In FFM mode,
the frequency spectrum of the Class D output consists of
the fundamental switching frequency and its associated
harmonics (see the Wideband Output Spectrum (FFM
Mode) graph in the Typical Operating Characteristics).
The MAX9713/ MAX9714 allow the switching frequency
to be changed by ±35%, should the frequency of one or
more of the harmonics fall in a sensitive band. This can
be done at any time and not affect audio reproduction.
V
IN
OUT+
OUT-
_______________________________________________________________________________________
= 0V
Fixed-Frequency Modulation (FFM) Mode
Detailed Description
Operating Modes
The MAX9713/MAX9714 feature a unique, patented
spread-spectrum mode that flattens the wideband
spectral components, improving EMI emissions that
may be radiated by the speaker and cables. This mode
is enabled by setting FS1 = FS2 = H. In SSM mode, the
switching frequency varies randomly by ±1.7%kHz
around the center frequency (335kHz). The modulation
scheme remains the same, but the period of the trian-
gle waveform changes from cycle to cycle. Instead of a
large amount of spectral energy present at multiples of
the switching frequency, the energy is now spread over
a bandwidth that increases with frequency. Above a
few megahertz, the wideband spectrum looks like white
noise for EMI purposes (Figure 2).
Efficiency of a Class D amplifier is attributed to the
region of operation of the output stage transistors. In a
Class D amplifier, the output transistors act as current-
steering switches and consume negligible additional
power. Any power loss associated with the Class D out-
put stage is mostly due to the I
on-resistance, and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is
78%, however that efficiency is only exhibited at peak
output powers. Under normal operating levels (typical
music reproduction levels), efficiency falls below 30%,
whereas the MAX9714 still exhibits >80% efficiencies
under the same conditions (Figure 3).
The MAX9713/MAX9714 have a shutdown mode that
reduces power consumption and extends battery life.
Driving SHDN low places the device in low-power
(0.2µA) shutdown mode. Connect SHDN to a logic high
for normal operation.
The MAX9713/MAX9714 feature comprehensive click-
and-pop suppression that eliminates audible transients
on startup and shutdown. While in shutdown, the H-
bridge is pulled to GND through 300kΩ. During startup,
Table 1. Operating Modes
FS1
H
H
L
L
Spread-Spectrum Modulation (SSM) Mode
Click-and-Pop Suppression
FS2
H
H
L
L
2
R loss of the MOSFET
SWITCHING MODE
335 ±7%
Efficiency
Shutdown
(kHz)
335
460
236