MAX13301 Datasheet, PDF (12/37 Pages) Maxim Integrated Products – 4-Channel, Automotive Class D Audio Amplifier Feedback After the Filter

4-Channel, Automotive Class D Audio Amplifier
I²C COMP
TRIANGLE WAVE
PWM LOGIC
REF
PWM
COMPARATOR
I2C COMP
OSC
REF
3-BIT ADC
FEED-
FORWARD
PVDD
REF
ERROR
REF
AMPLIFIER
AUDIO IN
REF
PREAMPLIFIER
Figure 1. Detailed Block Diagram of the MAX13301 Audio Path
Detailed Description
The MAX13301 4-channel, Class D audio power ampli-
fiers is specifically designed for automotive applications.
Integrated feedback from the LC filter’s output improves
the THD+N by reducing the distortion, providing Class
AB performance while achieving efficiency up to 90.5%.
The devices also support spread-spectrum modulation
for AM radio compatibility.
Description of Operation
The device emulates current-mode controllers with digital
feed-forward (Figure 1). The internal oscillator creates an
18MHz square wave. The I²C controls a clock divider that
divides down this high-frequency clock to a usable fre-
quency. The resulting square wave is integrated to create
a triangle wave. A 3-bit ADC converts the PVDD voltage
into a code that adjusts the resistors used in the triangle-
wave integrator. The triangle-wave amplitude becomes
progressively larger as PVDD increases. The triangle
wave is fed into the PWM comparator.
The two differential amplifiers provide both analog and
digital feedback. The feedback is summed with the out-
put of the preamplifier at the error amplifier. The output
of the error amplifier is an AC replica of the inductor cur-
rent (emulated current mode) and the triangle wave is
therefore the slope compensation. The PWM comparator
controls the full-bridge operation, turning on and off each
FET pair (double-edge modulation). To ensure that the
devices switch at the desired frequency, it is important
to ensure that the triangle wave is greater than the error-
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