MAX13301 Datasheet, PDF (14/37 Pages) Maxim Integrated Products – 4-Channel, Automotive Class D Audio Amplifier Feedback After the Filter

4-Channel, Automotive Class D Audio Amplifier
Shutdown
In shutdown, all circuitry including the fault monitors and
I²C interface is disabled to reduce power consumption
and extend battery life. Connect EN to logic-high for nor-
mal operation. Connect EN to GND to place the device in a
low-power shutdown mode. In shutdown, the devices draw
17mA (typ) from the battery.
Clock Source
The device supports fixed-frequency modulation with an
internal or external clock. The modulation mode is select-
ed through CTRL1.CM[1:0] (operating mode select bits).
Master Configuration
In master mode, 10 modulation frequencies are avail-
able in fixed-frequency modulation mode. Program
CTRL0.MDIV[3:0] (master clock-divide ratio bits) for the
desired frequency.
Slave Configuration
Configuring the device as a slave allows an external
clock source to provide the switching frequency. In this
case, apply the external clock signal at SYNC at double
the desired switching frequency.
Fixed-Frequency Modulation Mode
The devices supports a fixed-frequency modulation
mode with 10 different selectable frequencies between
300kHz and 750kHz. The frequency is selectable through
the I²C interface. The frequency spectrum consists of the
fundamental switching frequency and its associated
harmonics (see the wideband output spectrum graphs in
the Typical Operating Characteristics). For applications
where exact spectrum placement of the switching funda-
mental is important, program the switching frequency so
that the harmonics do not fall within a sensitive frequency
band.
Spread Spectrum
The device features a unique spread-sprectrum mode
that flattens the wideband spectral components, improv-
ing EMI emissions that can be radiated by the speaker
and cables. This feature is only available in master clock
mode and is enabled by setting the CTRL5.SS[2:0] and
CTRL5.SSEN bits. In spread-spectrum mode, the switch-
ing frequency vaies linearly by up to 7% depending on
CTRL5.SS[2:0] setting. The modulation scheme remains
the same, but the period of the triangle 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
14
purposes. A proprietary amplifier topology ensures this
does not significantly increase the noise floor in the
audio bandwidth.
Efficiency
The high efficiency of a Class D amplifier is due to the
switching 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
output 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% at
peak output power. Under normal operating levels (typi-
cal music reproduction levels), the efficiency falls below
30%, whereas the device exhibits > 80% efficiency
under the same conditions (Figure 2).
Current Limit
The current limit of the outputs is selectable between 7A
(typ) and 8.75A (typ) through the CTRL3.HCL bit.
When the current limit is exceeded, the affected output
is latched off and its corresponding overcurrent indica-
tor bit OSTAT0.OC[3:0] is set to 0. The device does
not attempt to activate the output until instructed by
the microcontroller to do so. After eliminating the cause
of the current limit, reactivate the output by setting
OSTAT0.OC[3:0] to 1.
Short to either ground or battery causes the output to be
latched off and its corresponding OSTAT0.OC[3:0] bit
to be set to 0. After removing the short, reactivate the
output by setting OSTAT0.OC[3:0] to 1.
MAX13301 EFFICIENCY vs.
IDEAL CLASS AB AMPLIFIER EFFICIENCY
100
90
80
70
MAX13301
60
50
40
IDEAL CLASS AB
AMPLIFIER
30
20
10
0
0
VPVDD = 14.4V
RL = 4I
5
10
15
20
25
OUTPUT POWER PER CHANNEL (W)
Figure 2. Efficiency vs. Output Power of Class AB Amplifier
and the MAX13301