max97000 Maxim Integrated Products, Inc., max97000 Datasheet - Page 21

• Manufacturer Part Number: max97000
• Description: Audio Subsystem With Mono Class D Speaker And Class H Headphone Amplifier
• Manufacturer: Maxim Integrated Products, Inc.

DirectDrive is a registered trademark of Maxim Integrated Products, Inc.
The MAX97000 speaker amplifiers integrate a limiter
to provide speaker protection and audio compression.
When enabled, the limiter monitors the audio signal at
the output of the Class D speaker amplifier and decreas-
es the gain if the distortion exceeds the predefined
threshold. The limiter automatically tracks the battery
voltage to reduce the gain as the battery voltage drops.
Figure 5 shows the typical output vs. input curves with
and without the distortion limiter. The dotted line shows
the maximum gain for a given distortion limit without
the distortion limiter. The solid line shows how, with the
distortion limiter enabled, the gain can be increased
without exceeding the set distortion limit. When the
limiter is enabled, selecting a high gain level results in
peak signals being attenuated while low signals are left
unchanged. This increases the perceived loudness with-
out the harshness of a clipped waveform.
The MAX97000 integrates a DPST analog audio switch.
This switch can be used to disconnect an independent
audio signal, or drive the 8I speaker by connecting
NC1 and NC2 to OUTN and OUTP, respectively. Unlike
discrete solutions, the switch design reduces coupling
of Class D switching noise to the COM_ inputs. This
eliminates the need for a costly T-switch. Drive COM1
and COM2 with a low-impedance source to minimize
noise on the pins. In applications that do not require
the analog switch, leave COM1, COM2, NC1, and NC2
unconnected.
Figure 5. Limiter Gain Curve
MAXIMUM THD+N
LEVEL
Speaker and Class H Headphone Amplifier
V
OUT
Audio Subsystem with Mono Class D
Distortion Limiter
Analog Switch
V
IN
Traditional single-supply headphone amplifiers have
outputs biased at a nominal DC voltage (typically half
the supply). Large coupling capacitors are needed to
block this DC bias from the headphone. Without these
capacitors, a significant amount of DC current flows to
the headphone, resulting in unnecessary power dis-
sipation and possible damage to both headphone and
headphone amplifier.
Maxim’s patented DirectDrive
charge pump to create an internal negative supply
voltage. This allows the headphone outputs of the
MAX97000 to be biased at GND while operating from a
single supply (Figure 6). Without a DC component, there
is no need for the large DC-blocking capacitors. Instead
of two large (220FF, typ) capacitors, the MAX97000
charge pump requires three small ceramic capacitors,
Figure 6. Traditional Amplifier Output vs. MAX97000
DirectDrive Output
CONVENTIONAL AMPLIFIER BIASING SCHEME
DirectDrive AMPLIFIER BIASING SCHEME
Headphone Amplifier
®
architecture uses a
DirectDrive
V
V
GND
+V
SGND
-V
DD
DD
DD
DD
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