max97200 Maxim Integrated Products, Inc., max97200 Datasheet - Page 10

• Manufacturer Part Number: max97200
• Description: Low-power, Low-offset, Dual Mode, Class H Directdrive Headphone Amplifier
• Manufacturer: Maxim Integrated Products, Inc.

Low-Power, Low-Offset, Dual Mode, Class H
DirectDrive Headphone Amplifier
R
such that f
interest. Setting f
frequency. Capacitors with higher voltage coefficients,
such as ceramics, result in increased distortion at low
frequencies.
Use capacitors with an ESR less than 100mI for opti-
mum performance. Low ESR ceramic capacitors mini-
mize the output resistance of the charge pump. For best
performance over the extended temperature range,
select capacitors with an X7R dielectric.
The value of the flying capacitor (C1) affects the load
regulation and output resistance of the charge pump. A
C1 value that is too small degrades the device’s ability
to provide sufficient current drive, which leads to a loss
of output voltage. Connect a 1FF capacitor between C1P
and C1N.
The output capacitor value and ESR directly affect the
ripple at PVSS. Increasing the value of C2 and C3 reduc-
es output ripple. Likewise, decreasing the ESR of C2 and
C3 reduces both ripple and output resistance. Lower
capacitance values can be used in systems with low
maximum output power levels. Connect a 1FF capaci-
tor between PVDD and PGND. Connect a 1FF capacitor
between PVSS and PGND.
Improvements to both layout and component selec-
tion can decrease the MAX97200 susceptibility to RF
noise and prevent RF signals from being demodulated
into audible noise. Trace lengths should be kept below
¼ of the wavelength of the RF frequency of interest.
Minimizing the trace lengths prevents the traces from
functioning as antennas and coupling RF signals into the
MAX97200. The wavelength (
where c = 3 x 10
interest.
Route audio signals to the middle layers of the PCB to
allow the ground planes above and below to shield them
from RF interference. Ideally, the top and bottom layers
of the PCB should primarily be ground planes to create
effective shielding.
10
IN
is the amplifier’s input resistance value. Choose C
_____________________________________________________________________________________
-3dB
is well below the lowest frequency of
-3dB
8
Charge-Pump Capacitor Selection
m/s, and f is the RF frequency of
too high affects the amplifier’s low
λ
= c/f
Output Capacitors (C2, C3)
λ)
in meters is given by:
Flying Capacitor (C1)
RF Susceptibility
IN
Figure 3. Headphone RF Immunity
Additional RF immunity can also be obtained from rely-
ing on the self-resonant frequency of capacitors as
it exhibits the frequency response similar to a notch
filter. Depending on the manufacturer, 10pF to 20pF
capacitors typically exhibit self resonance at RF frequen-
cies. These capacitors when placed at the input pins
can effectively shunt the RF noise at the inputs of the
MAX97200. For these capacitors to be effective, provide
a low-impedance, low-inductance path from the capaci-
tors to the ground plane. Do not use microvias to con-
nect to the ground plane as these vias do not conduct
well at RF frequencies. Figure 3 shows headphone RF
immunity with a well laid out PCB.
Proper layout and grounding are essential for optimum
performance. Use large traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance, as well as route heat away
from the device. Good grounding improves audio per-
formance, minimizes crosstalk between channels, and
prevents switching noise from coupling into the audio
signal. Connect PGND and GND together at a single
point on the PCB. Route PGND and all traces that carry
switching transients away from GND, and the traces and
components in the audio signal path.
Connect C2 to the PGND plane. Place the charge-pump
capacitors (C1, C2) as close as possible to the device.
Bypass PVDD with a 1FF capacitor to PGND. Place the
bypass capacitors as close as possible to the device.
-100
-10
-20
-30
-40
-50
-60
-70
-80
-90
0
1000
HEADPHONE RF IMMUNITY
LEFT CHANNEL
1500
vs. FREQUENCY
FREQUENCY (MHz)
RIGHT CHANNEL
Layout and Grounding
2000
2500
3000