MAX97001EWP+ MAXIM [Maxim Integrated Products], MAX97001EWP+ Datasheet - Page 21

• Manufacturer Part Number: MAX97001EWP+
• Description: Audio Subsystem with Mono Class D Speaker and Class H Headphone Amplifiers
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX97001 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 MAX97001 integrates a DPST analog audio switch
that connects COM1 and COM2 to OUTP and OUTN,
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 and COM2 uncon-
nected. When applying signal on COM1 and COM2, dis-
able the Class D amplifier before closing the switch.
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
MAX97001 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 MAX97001
charge pump requires two small ceramic capacitors,
conserving board space, reducing cost, and improving
the frequency response of the headphone amplifier.
Audio Subsystem with Mono Class D Speaker
Headphone Amplifier
®
and Class H Headphone Amplifiers
architecture uses a
Distortion Limiter
Analog Switch
DirectDrive
Figure 5. Limiter Gain Curve
Figure 6. Traditional Amplifier Output vs. MAX97001
DirectDrive Output
DirectDrive is a registered trademark of Maxim Integrated
Products, Inc.
See the Output Power vs. Load Resistance graph in the
Typical Operating Characteristics for details of the pos-
sible capacitor sizes. There is a low DC voltage on the
amplifier outputs due to amplifier offset. However, the
offset of the MAX97001 is typically Q0.6mV, which, when
combined with a 32I load, results in less than 50FA of
DC current flow to the headphones.
CONVENTIONAL AMPLIFIER BIASING SCHEME
MAXIMUM THD+N
DirectDrive AMPLIFIER BIASING SCHEME
LEVEL
V
OUT
V
GND
+V
SGND
IN
V
V
-V
DD
DD
DD
DD
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