max9789a Maxim Integrated Products, Inc., max9789a Datasheet - Page 16

• Manufacturer Part Number: max9789a
• Description: Windows Vista-compliant, Stereo Class Ab Speaker Amplifiers And Directdrive Headphone Amplifiers Integrated Products
• Manufacturer: Maxim Integrated Products, Inc.

Windows Vista-Compliant, Stereo Class AB Speaker
Amplifiers and DirectDrive Headphone Amplifiers
The MAX9789A/MAX9790A feature control inputs for the
independent enabling of the speaker and headphone
amplifiers, allowing both to be active simultaneously if
required. Driving SPKR_EN high disables the speaker
amplifiers. Driving HP_EN low independently disables
the headphone amplifiers. For applications that require
only one of the amplifiers to be on at a given time,
SPKR_EN and HP_EN can be tied together allowing a
single logic voltage to enable either the speaker or the
headphone amplifier as shown in Figure 4.
The MAX9789A/MAX9790A allow for the speaker and
headphone amplifiers to be muted. By driving MUTE
low, both the speaker and headphone amplifiers are
muted. When muted, the speaker outputs remain
biased at V
The MAX9789A/MAX9790A feature a low-power shut-
down mode, drawing 0.3µA of supply current. By dis-
abling the speaker, headphone amplifiers and the LDO
(for MAX9789A), the MAX9789A/MAX9790A enter low-
power shutdown mode. Set SPKR_EN to V
HP_EN and LDO_EN to GND to disable the speaker
amplifiers, headphone amplifiers, and LDO, respectively.
The MAX9789A/MAX9790A speaker amplifiers feature
Maxim’s comprehensive, industry-leading click-and-
pop suppression. During startup, the click-and-pop
suppression circuitry eliminates any audible transient
sources internal to the device. When entering shut-
down, the differential speaker outputs ramp to GND
quickly and simultaneously.
Figure 4. Enabling Either the Speaker or Headphone Amplifier
with a Single Control Pin
16
CONTROL PIN
______________________________________________________________________________________
SINGLE
DD
/ 2.
Click-and-Pop Suppression
Speaker and Headphone
SPKR_EN
HP_EN
MAX9789A/MAX9790A
Amplifier Enable
Speaker Amplifier
Shutdown
DD
MUTE
and
In conventional single-supply headphone amplifiers, the
output-coupling capacitor is a major contributor of audi-
ble clicks and pops. Upon startup, the amplifier charges
the coupling capacitor to its bias voltage, typically
V
charged to GND. A DC shift across the capacitor results,
which in turn, appears as an audible transient at the
headphone. Since the MAX9789A/MAX9790A do not
require output-coupling capacitors, no audible transient
occurs.
Additionally, the MAX9789A/MAX9790A features exten-
sive click-and-pop suppression that eliminates any
audible transient sources internal to the device. The
startup/shutdown waveform in the Typical Operating
Characteristics shows that there are minimal spectral
components in the audible range at the output.
The MAX9789A/MAX9790A feature speaker amplifiers
designed to drive a load differentially, a configuration
referred to as bridge-tied load (BTL). The BTL configu-
ration (Figure 5) offers advantages over the single-
ended configuration, where one side of the load is
connected to ground. Driving the load differentially
doubles the output voltage compared to a single-
ended amplifier operating under similar conditions. The
doubling of the output voltage yields four times the out-
put power at the load.
Since the differential outputs are biased at mid-supply,
there is no net DC voltage across the load. This elimi-
nates the need for DC-blocking capacitors required for
single-ended amplifiers. These capacitors can be
large, expensive, consume board space, and degrade
low-frequency performance.
Figure 5. Bridge-Tied Load Configuration
DD
/ 2. Likewise, during shutdown, the capacitor is dis-
Applications Information
+1
-1
BTL Speaker Amplifiers
Headphone Amplifier
V
2 x V
V
OUT(P-P)
OUT(P-P)
OUT(P-P)