MAX1782ETM+C8C Maxim Integrated, MAX1782ETM+C8C Datasheet - Page 12

• Manufacturer Part Number: MAX1782ETM+C8C
• Description: Battery Management Adv Smart Battery Pack Controller
• Manufacturer: Maxim Integrated
• Series: MAX1782r

Specifications of MAX1782ETM+C8C

• Rohs: yes

10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Amplifiers
used if a design is failing radiated emissions due to
board layout or cable length, or the circuit is near EMI-
sensitive devices. Use a ferrite bead filter when radiat-
ed frequencies above 10MHz are of concern. Use an
LC filter when radiated frequencies below 10MHz are of
concern, or when long leads connect the amplifier to
the speaker. Refer to the MAX9704 Evaluation Kit
schematic for details of this filter.
In certain systems, a single audio source can be shared
by multiple devices (speaker and headphone ampli-
fiers). When sharing inputs, it is common to mute the
unused device, rather than completely shutting it down,
preventing the unused device inputs from distorting the
input signal. Mute the MAX9703/MAX9704 by driving SS
low through an open-drain output or MOSFET (see the
System Diagram). Driving SS low turns off the Class D
output stage, but does not affect the input bias levels of
the MAX9703/MAX9704. Be aware that during normal
operation, the voltage at SS can be up to 7V, depending
on the MAX9703/MAX9704 supply.
Proper power-supply bypassing ensures low distortion
operation. For optimum performance, bypass V
PGND with a 0.1µF capacitor as close to each V
as possible. A low-impedance, high-current power-sup-
ply connection to V
capacitance should be added as required depending on
the application and power-supply characteristics. AGND
and PGND should be star connected to system ground.
Refer to the MAX9704 Evaluation Kit for layout guidance.
Class D amplifiers provide much better efficiency and
thermal performance than a comparable Class AB ampli-
fier. However, the system’s thermal performance must be
considered with realistic expectations and include con-
sideration of many parameters. This section examines
Class D amplifiers using general examples to illustrate
good design practices.
When a Class D amplifier is evaluated in the lab, often a
continuous sine wave is used as the signal source. While
this is convenient for measurement purposes, it repre-
sents a worst-case scenario for thermal loading on the
amplifier. It is not uncommon for a Class D amplifier to
enter thermal shutdown if driven near maximum output
power with a continuous sine wave.
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______________________________________________________________________________________
Continuous Sine Wave vs. Music
Thermal Considerations
DD
is assumed. Additional bulk
Sharing Input Sources
Supply Bypassing/Layout
Class D Amplifier
DD
DD
pin
to
Audio content, both music and voice, has a much lower
RMS value relative to its peak output power. Figure 5
shows a sine wave and an audio signal in the time
domain. Both are measured for RMS value by the oscillo-
scope. Although the audio signal has a slightly higher
peak value than the sine wave, its RMS value is almost
half that of the sine wave. Therefore, while an audio sig-
nal may reach similar peaks as a continuous sine wave,
the actual thermal impact on the Class D amplifier is
highly reduced. If the thermal performance of a system is
being evaluated, it is important to use actual audio sig-
nals instead of sine waves for testing. If sine waves must
be used, the thermal performance will be less than the
system’s actual capability.
The exposed pad is the primary route of keeping heat
away from the IC. With a bottom-side exposed pad, the
PC board and its copper becomes the primary heatsink
for the Class D amplifier. Solder the exposed pad to a
large copper polygon. Add as much copper as possible
from this polygon to any adjacent pin on the Class D
amplifier as well as to any adjacent components, provid-
ed these connections are at the same potential. These
copper paths must be as wide as possible. Each of
these paths contributes to the overall thermal capabilities
of the system.
The copper polygon to which the exposed pad is
attached should have multiple vias to the opposite side
of the PC board, where they connect to another copper
polygon. Make this polygon as large as possible within
the system’s constraints for signal routing.
Figure 5. RMS Comparison of Sine Wave vs. Audio Signal
PC Board Thermal Considerations
20ms/div