MAX9770ETI+ Maxim Integrated Products, MAX9770ETI+ Datasheet - Page 17

• 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

Although this movement is small, a speaker not designed
to handle the additional power may be damaged. For
optimum results, use a speaker with a series inductance
>10µH. Typical small 8Ω speakers exhibit series induc-
tances in the range of 20µH to 100µH.
Unlike Class AB amplifiers, the output offset voltage of a
Class D amplifier does not noticeably increase quiescent
current draw when a load is applied. This is due to the
power conversion of the Class D amplifier. For example, a
15mV DC offset across an 8Ω load results in 1.9mA extra
current consumption in a Class AB device. In the Class D
case, a 15mV offset into 8Ω equates to an additional
power drain of 28µW. Due to the high efficiency of the
Class D amplifier, this represents an additional quiescent
current draw of 28µW/(V
order of a few microamps.
The MAX9770 has different supplies for each portion of
the device, allowing for the optimum combination of
headroom and power dissipation and noise immunity.
The speaker amplifier is powered from PV
ranges from 2.5V to 5.5V. The headphone amplifiers
are powered from V
supply of the headphone amplifiers and ranges from
2.5V to 5.5V. SV
phone amplifiers. Connect SV
pump is powered by CPV
to 5.5V and should be the same potential as V
charge pump inverts the voltage at CPV
resulting voltage appears at CPV
the device is powered by V
The input capacitor (C
fier input resistance (R
removes the DC bias from an incoming signal (see the
Block Diagram ). The AC-coupling capacitor allows the
amplifier to bias the signal to an optimum DC level.
Assuming zero-source impedance, the -3dB point of
the highpass filter is given by:
R
given in the Electrical Characteristics . Be aware that
the MONO input has a lower input impedance than the
other inputs. Choose C
lowest frequency of interest. Setting f
IN
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
is the amplifier’s internal input resistance value
with Stereo DirectDrive Headphone Amplifiers
SS
______________________________________________________________________________________
f
−
is the negative supply of the head-
3
DD
dB
IN
IN
IN
), in conjunction with the ampli-
and SV
DD
=
), forms a highpass filter that
DD
such that f
DD
Component Selection
2 π
/ 100 x η), which is on the
. CPV
.
SS
R C
IN IN
1
SS
to CPV
SS
. V
DD
Power Supplies
. The remainder of
DD
-3dB
Output Offset
ranges from 2.5V
SS
is the positive
-3dB
. The charge
DD
is below the
Input Filter
DD
, and the
too high
DD
. PV
. The
DD
affects the amplifier’s low-frequency response. Setting
f
Use capacitors with low-voltage coefficient dielectrics,
such as tantalum or aluminum electrolytic. Capacitors
with high-voltage coefficients, such as ceramics, may
result in increased distortion at low frequencies.
The MAX9770 speaker amplifier does not require an out-
put filter for normal operation and audio reproduction. The
device passes FCC Class B radiated emissions stan-
dards with 100mm of unshielded speaker cables.
However, output filtering can be used if a design is failing
radiated emissions due to board layout or cable length,
or if the circuit is near EMI-sensitive devices. Use a com-
mon-mode choke connected in series with the speaker
outputs if board space is limited and emissions are a
concern. Use of an LC filter is necessary if excessive
speaker cable is used.
BIAS is the output of the internally generated DC bias
voltage. The BIAS bypass capacitor, C
PSRR and THD+N by reducing power supply and other
noise sources at the common-mode bias node, and
also generates the clickless/popless, startup/shutdown
DC bias waveforms for the speaker amplifiers. Bypass
BIAS with a 0.047µF capacitor to GND.
-3dB
too low can affect the click-and-pop performance.
BIAS Capacitor
BIAS
Output Filter
improves
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