MAX98090BEWJ+T Maxim Integrated, MAX98090BEWJ+T Datasheet - Page 161

• Manufacturer Part Number: MAX98090BEWJ+T
• Description: Interface - CODECs 5V 130mW Stereo Headphone Amp
• Manufacturer: Maxim Integrated

MAX98090
Component Selection
AC-Coupling Capacitors
An input capacitor, C
impedance of the device line inputs forms a highpass
filter that removes the DC bias from an incoming analog
signal. The AC-coupling capacitor allows the amplifier
to automatically bias the signal to an optimum DC level.
Assuming very low source impedance (comparatively),
the -3dB point of the highpass filter is given by:
Choose C
quency of interest. For best audio quality, use capacitors
whose dielectrics have low-voltage coefficients, such
as tantalum or aluminum electrolytic. Capacitors with
high-voltage coefficients, such as ceramics, can result
in increased distortion at low frequencies. If needed, line
output AC-coupling capacitor values can be calculated in
similar fashion by using the input resistance of the output
stage connected to the line output drivers.
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩ for optimum
performance. Low-ESR ceramic capacitors minimize
the output resistance of the charge pump. Most surface
mount ceramic capacitors satisfy the ESR requirement.
For best performance over the extended temperature
range, select capacitors with an X7R dielectric.
The value of the flying capacitor (connected between
C1N and C1P) affects the output resistance of the charge
pump. A value that is too small degrades the device’s
ability to provide sufficient current drive, which leads to a
loss of output voltage. Increasing the value of the flying
capacitor reduces the charge-pump output resistance to
an extent. Above 1µF, the on-resistance of the internal
switches and the ESR of external charge pump capaci-
tors dominate.
www.maximintegrated.com
IN
such that f
f
−
3dB
IN
=
-3dB
, in conjunction with the input
2
π ×
is well below the lowest fre-
R
IN
1
×
C
IN
The holding capacitor (bypassing HPVSS) value and ESR
directly affect the ripple at HPVSS. Increasing the capaci-
tor’s value reduces output ripple. Likewise, decreasing
the ESR reduces both ripple and output resistance. Lower
capacitance values can be used in systems with low maxi-
mum output power levels. See the Output Power vs. Load
Resistance graph in the
section for more information.
Filterless Class D Speaker Operation
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 amplifier,
and can decrease efficiency and THD+N performance.
The traditional PWM scheme uses large differential output
swings (2 x SPK_VDD peak to peak) and causes large
ripple currents. Any parasitic resistance in the filter com-
ponents results in a loss of power, lowering the efficiency.
For typical applications (such as handsets, pads, etc.)
where the trace length from driver the speaker is short
and low impedance, the device 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 Class D output filter
results in a smaller, less costly, and more efficient solution.
In cases where the trace/wire length is long, and/or series
resistance/inductance is high, an output LC filter might be
required. In such a case, if the nominal impedance of the
load is not constant over the entire audio band, a Zobel
(impedance matching) circuit might be required.
Because the frequency of the IC’s output is well beyond
the bandwidth of most speakers, voice coil movement due
to the square-wave frequency is very small. Although this
movement is small, a speaker not designed to handle the
additional power can be damaged. For optimum results,
use a speaker with a series inductance > 10µH. Typical
8Ω speakers exhibit series inductances in the 20µH to
100µH range.
Ultra-Low Power Stereo Audio Codec
Typical Operating Characteristics
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