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MAX97220A Datasheet(PDF) 13 Page - Maxim Integrated Products

Part No. MAX97220A
Description  Differential Input DirectDrive Line Drivers/Headphone Amplifiers
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Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com
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MAX97220A Datasheet(HTML) 13 Page - Maxim Integrated Products

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Maxim Integrated
Differential Input DirectDrive
Line Drivers/Headphone Amplifiers
MAX97220A–MAX97220E
DirectDrive
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typically
half the supply) for maximum dynamic range. Large cou-
pling 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 dissipation and possible damage to
both the headphone and the headphone amplifier.
Maxim’s patented DirectDrive architecture uses a charge
pump to create an internal negative supply voltage,
allowing the IC's outputs to be biased about PGND.
With no DC component, there is no need for the large
DC-blocking capacitors. Instead of two large (220FF,
typ) tantalum capacitors, the IC charge pump requires
two small ceramic capacitors, conserving board space,
reducing cost, and improving the frequency response of
the headphone amplifier.
Input Filter
In addition to the cost and size disadvantages of
DC-blocking capacitors required by conventional head-
phone amplifiers, these capacitors limit the amplifier’s
low-frequency response and can distort the audio signal.
If input capacitors are used, input capacitor CIN, in con-
junction with internal input resistor RIN, forms a highpass
filter that removes the DC bias from an incoming signal.
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:
-3dB
IN IN
1
f
2R C
=
π
Setting f-3dB too high affects the low-frequency response
of the amplifier. Use capacitors with adequately low volt-
age coefficients, such as X7R ceramic capacitors with a
high voltage rating. Capacitors with higher voltage coef-
ficients result in increased distortion at low frequencies.
BIAS Capacitor
Bypass BIAS with a 0.1FF capacitor to PGND. Do not
connect external loads to BIAS.
Charge Pump
The MAX97220_ features a low-noise charge pump. The
500kHz switching frequency is well beyond the audio
range and, thus, does not interfere with the audio sig-
nals. The switch drivers feature a controlled switching
speed that minimizes noise generated by turn-on and
turn-off transients. By limiting the switching speed of the
charge pump, the di/dt noise caused by the parasitic
bond wire and trace inductance is minimized. The IC
requires a 1FF flying capacitor between C1P and C1N
and a 1FF hold capacitor from PVSS to PGND.
Click-and-Pop Suppression
The IC features Maxim’s industry-leading click-and-pop
suppression circuitry. When entering shutdown, the
amplifier outputs are high impedance to ground. This
scheme minimizes the energy present in the audio band.
Shutdown
The IC features a 1FA low-power shutdown mode
that reduces power consumption. When the active-low
shutdown mode is entered, the device’s internal bias
circuitry is disabled, the amplifier outputs go high imped-
ance, and BIAS is driven to PGND. The MAX97220A/
MAX97220B/MAX97220E inputs are driven to PGND.
Figure 3. Pseudo-Differential Input Configuration
OUT
AUDIO
CODEC
RF1*
RIN1*
IN-
OUT
GND
IN+
RIN2
RIN1 = RIN2, RF1 = RF2
*RIN1 AND RF1 ARE INTERNAL FOR MAX97220C/MAX97220D
RF2


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