max97001 Maxim Integrated Products, Inc., max97001 Datasheet - Page 34

• Manufacturer Part Number: max97001
• Description: Audio Subsystem With Mono Class D Speaker And Class H Headphone Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

Audio Subsystem with Mono Class D Speaker
and Class H Headphone Amplifiers
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 frequencies. These
capacitors when placed at the input pins can effectively
shunt the RF noise at the inputs of the MAX97001. For
these capacitors to be effective, they must have a low-
impedance, low-inductance path to the ground plane.
Do not use microvias to connect to the ground plane as
these vias do not conduct well at RF frequencies.
Additional EMI suppression can be achieved using a
filter constructed from a ferrite bead and a capacitor to
ground (Figure 14). Use a ferrite bead with low DC resis-
tance, high-frequency (> 600MHz) impedance between
100I and 600I, and rated for at least 1A. The capacitor
value varies based on the ferrite bead chosen and the
actual speaker lead length. Select a capacitor less than
1nF based on EMI performance.
An input capacitor, C
impedance of the MAX97001 line inputs forms a high-
pass 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 zero-source impedance, 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, may result in
increased distortion at low frequencies.
Use capacitors with an ESR less than 100mI 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.
34
IN
such that f
f
-3dB
Charge-Pump Capacitor Selection
IN
-3dB
=
, in conjunction with the input
2 R C
Optional Ferrite Bead Filter
π
is well below the lowest fre-
Component Selection
IN IN
1
Input Capacitor
Figure 14. Optional Class D Ferrite Bead Filter
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 1FF, the on-resistance
of the internal switches and the ESR of external charge-
pump capacitors dominate.
The holding capacitor (bypassing HPVDD and HPVSS)
value and ESR directly affect the ripple on the supply.
Increasing the capacitor’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 maximum output power levels.
See the Output Power vs. Load Resistance graph in the
Typical Operating Characteristics for more information
Proper layout and grounding are essential for opti-
mum performance. Use a large continuous ground
plane on a dedicated layer of the PCB to minimize
loop areas. Connect GND directly to the ground plane
using the shortest trace length possible. Proper ground-
ing improves audio performance, minimizes crosstalk
between channels, and prevents any digital noise from
coupling into the analog audio signals.
Place the capacitor between C1P and C1N as close
to the MAX97001 as possible to minimize trace length
from C1P to C1N. Inductance and resistance added
between C1P and C1N reduce the output power of the
headphone amplifier. Bypass HPVDD and HPVSS with
capacitors located close to the pins with a short trace
length to GND. Close decoupling of HPVDD and HPVSS
minimizes supply ripple and maximizes output power
from the headphone amplifier.
Supply Bypassing, Layout, and Grounding
MAX97001
OUT+
OUT-
Charge-Pump Holding Capacitor
Charge-Pump Flying Capacitor