MAX9770ETI+ Maxim Integrated Products, MAX9770ETI+ Datasheet - Page 16

• Manufacturer Part Number: MAX9770ETI+
• Description: IC AMP AUDIO 1.2W MONO D 28TQFN
• Manufacturer: Maxim Integrated Products
• Type: Class Dr

Specifications of MAX9770ETI+

• Output Type: 1-Channel (Mono) with Stereo Headphones
• Max Output Power X Channels @ Load: 1.2W x 1 @ 8 Ohm; 80mW x 2 @ 16 Ohm
• Voltage - Supply: 2.5 V ~ 5.5 V
• Features: Depop, Input Multiplexer, Mute, Short-Circuit and Thermal Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 28-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

the device changes when a headphone is inserted or
removed. For example, the block diagram shows HPS
connected to GAIN2, while GAIN1 is connected to V
In this configuration, the gain in speaker mode is 9dB,
while the gain in headphone mode is 1dB. The gain
settings with the HPS connection are shown in Table 4.
The MAX9770 features a 0.1µA, low-power shutdown
mode that reduces quiescent current consumption and
extends battery life. Drive SHDN low to disable the
drive amplifiers, bias circuitry, and charge pump. Bias
is driven to GND and the headphone amplifier output
impedance is 10kΩ in shutdown. Connect SHDN to
V
The MAX9770 speaker amplifier features comprehen-
sive click-and-pop suppression that eliminates audible
transients on startup and shutdown. While in shutdown,
the H-bridge is in a high-impedance state. During start-
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
Table 3. Gain Selection
Table 4. Gain Settings with HPS
Connection
16
G A I N 1 G A I N 2
DD
HPS
HPS
HPS
GAIN1
0
1
0
0
1
1
0
0
1
1
for normal operation.
______________________________________________________________________________________
HPS
HPS
HPS
0
1
0
1
0
1
GAIN2
MAX9770 SPEAKER
0
1
0
1
MODE GAIN
(HPS = 0)
Click-and-Pop Suppression
(dB)
SPEAKER GAIN
6
3
6
9
6
6
3
9
0
MAX9770
(dB)
6
3
9
0
HEADPHONE MODE
Speaker Amplifier
HEADPHONE
(HPS = 1)
Shutdown
GAIN
(dB)
-2
-2
GAIN
1
4
1
1
7
4
1
(dB)
-2
7
4
1
DD
.
up or power-up, the input amplifiers are muted and an
internal loop sets the modulator bias voltages to the cor-
rect levels, preventing clicks and pops when the H-
bridge is subsequently enabled. A soft-start function
unmutes the input amplifiers 30ms after startup.
In conventional single-supply headphone drivers, the
output-coupling capacitor is a major contributor of
audible clicks and pops. Upon startup, the driver
charges the coupling capacitor to its bias voltage, typi-
cally half the supply. Likewise, during shutdown, the
capacitor is discharged to GND. This results in a DC
shift across the capacitor, which in turn, appears as an
audible transient at the speaker. Since the MAX9770
headphone amplifier does not require output-coupling
capacitors, this does not arise.
Additionally, the MAX9770 features extensive click-and-
pop suppression that eliminates any audible transient
sources internal to the device. The Exiting Shutdown
(Headphone Mode) and Entering Shutdown (Headphone
Mode) graphs in the Typical Operating Characteristics
shows that there are minimal spectral components in the
audible range at the output upon startup or shutdown.
In most applications, the output of the preamplifier dri-
ving the MAX9770 has a DC bias of typically half the
supply. During startup, the input-coupling capacitor is
charged to the preamplifier’s DC bias voltage through
the R
capacitor and an audible click-and-pop. An internal
delay of 50ms eliminates the click-and-pop caused by
the input filter.
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s output. The
filters add cost, increase the solution size of the amplifi-
er, and can decrease efficiency. The traditional PWM
scheme uses large differential output swings (2 x V
peak-to-peak) at idle and causes large ripple currents.
Any parasitic resistance in the filter components results
in a loss of power, lowering efficiency.
The MAX9770 does not require an output filter. The
device relies on the inherent inductance of the speaker
coil and the natural filtering of both the speaker and the
human ear to recover the audio component of the
square-wave output. Eliminating the output filter results in
a smaller, less costly, and more efficient solution.
Because the frequency of the MAX9770 output is well
beyond the bandwidth of most speakers, voice coil
movement due to the square-wave frequency is minimal.
F
of the MAX9770, resulting in a DC shift across the
Applications Information
Filterless Operation
Headphone Amplifier
DD