MAX9713 데이터 시트보기 (PDF) - Maxim Integrated
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MAX9713 Datasheet PDF : 18 Pages
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6W, Filterless, Spread-Spectrum
Mono/Stereo Class D Amplifiers
Detailed Description
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.
Operating Modes
Fixed-Frequency Modulation (FFM) Mode
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.
VIN = 0V
OUT-
OUT+
Figure 1. MAX9714 Outputs with No Input Signal Applied
Table 1. Operating Modes
FS1
FS2
SWITCHING MODE
(kHz)
L
L
335
L
H
460
H
L
236
H
H
335 ±7%
Spread-Spectrum Modulation (SSM) Mode
The MAX9713/MAX9714 feature a unique spread-spec-
trum mode that flattens the wideband spectral compo-
nents, 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 fre-
quency varies randomly by ±1.7%kHz around the cen-
ter frequency (335kHz). The modulation scheme
remains the same, but the period of the triangle wave-
form 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
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 I2R loss of the MOSFET
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).
Shutdown
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.
Click-and-Pop Suppression
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,
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