Rainbow Electronics MAX98314 - Manual (Page 10)

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MAX98314
Mono 3.2W Class D Amplifier
with Integrated Input Coupling Capacitors
Detailed Description
The MAX98314 features low quiescent current, a low-
power shutdown mode, comprehensive click-and-pop
suppression, and excellent RF immunity.
The IC offers Class AB audio performance with Class D
efficiency in a minimal board-space solution. The Class
D amplifier features spread-spectrum modulation, edge-
rate, and overshoot control circuitry that offers significant
improvements to switch-mode amplifier radiated emis-
sions.
The amplifier features click-and-pop suppression that
reduces audible transients on startup and shutdown.
The amplifier additionally includes thermal overload and
short-circuit protection.
Highly linear, integrated input coupling capacitors (C
IN
)
reduce solution size and provide excellent THD+N,
PSRR, and CMRR performance at low frequencies vs.
standard Class D amplifiers using external input capaci-
tors.
Class D Speaker Amplifier
The IC’s filterless Class D amplifier offers much higher
efficiency than Class AB amplifiers. The high efficiency
of a Class D amplifier is due to the switching operation of
the output stage transistors. Any power loss associated
with the Class D output stage is mostly due to the I
2 R loss
of the MOSFET on-resistance and quiescent switching
current overhead.
Ultra-Low EMI Filterless Output Stage
Traditional Class D amplifiers require the use of external
LC filters, or shielding, to meet electromagnetic inter-
ference (EMI) regulation standards. Maxim’s patented
active emissions limiting edge-rate control circuitry and
spread-spectrum modulation reduces EMI emissions,
while maintaining up to 93% efficiency.
The spread-spectrum modulation mode flattens wide-
band spectral components, while proprietary techniques
ensure that the cycle-to-cycle variation of the switching
period does not degrade audio reproduction or effi-
ciency. The IC’s spread-spectrum modulator randomly
varies the switching frequency by Q20kHz around the
center frequency (300kHz). Above 10MHz, the wideband
spectrum looks like noise for EMI purposes (
Figure 1 ).
Amplifier Current Limit
If the output current of the speaker amplifier exceeds the
current limit (2.8A typ), the IC disables the outputs for
approximately 100Fs. At the end of 100Fs, the outputs
are reenabled. If the fault condition still exists, the IC
continues to disable and reenable the outputs until the
fault condition is removed.
Selectable Amplifier Gain
The IC offers five programmable gain settings, selectable
by a single gain input (GAIN).
Table 1. GAIN Selection
Integrated Input Coupling Capacitors (C
IN
)
The IC integrates two 0.011FF input coupling capacitors,
C
IN
. The input coupling capacitors, in conjunction with
the amplifier’s internal input resistance (R
IN
), form a first-
order highpass filter that removes the DC bias from the
incoming signal. These capacitors allow the amplifier to
bias the signal to an optimum DC level.
Figure 1. EMI Performance with 60cm of Speaker Cable, No
Output Filter
GAIN PIN MAXIMUM GAIN (dB)
Connect to PGND 12
Connect to PGND through
100kI Q5%
9
Connect to PVDD 6
Connect to PVDD through
100kI Q5%
3
Unconnected 0
90
70
50
30
10
-10
0 100 200 300 400 500 600 700 800 900 1000
EMISSIONS LEVEL (dBµV/m)
FREQUENCY (MHz)
EN5502B LIMIT
HORIZONTAL
VERTICAL