max9738 Maxim Integrated Products, Inc., max9738 Datasheet - Page 11

• Manufacturer Part Number: max9738
• Description: 16vp-p Class G Amplifier With Inverting Boost Converter
• Manufacturer: Maxim Integrated Products, Inc.

Figure 3. Driving a Ceramic Speaker
The AC-coupling capacitors (C
(R
an input signal (see the Typical Application Circuit/
Functional Diagram ). C
from appearing at the amplifier outputs. The -3dB point of
the highpass filter, assuming zero source impedance due
to the input signal source, is given by:
Ceramic speakers generally perform best at frequen-
cies greater than 1kHz. To reduce low-frequency dis-
tortion that may be added by the ceramic speakers
low-frequency response, select a C
f
the ceramic speaker. Use capacitors with low-voltage
coefficient dielectrics. Aluminum electrolytic, tantalum,
or film dielectric capacitors are good choices for AC-
coupling capacitors. Capacitors with high-voltage coef-
ficients, such as ceramics (non-C0G dielectrics), can
result in increased distortion at low frequencies.
The total output voltage ripple has two components: the
capacitive ripple caused by the charging and
-3dB
IN_
Boost Converter Output Capacitor Selection (C1)
) form highpass filters that remove any DC bias from
closely matches the low-frequency response of
MAX9738
f
−
3
dB
CLASS G
OUTPUT
STAGE
______________________________________________________________________________________
=
Input Coupling Capacitors (C
2
IN_
π
×
blocks the input signal source
R
Component Selection
OUT+
IN
OUT-
1
×
IN_
C
IN
) and input resistors
R
L
( )
Hz
IN
such that the
16V
IN_
P-P
Inverting Boost Converter
)
discharging of the output capacitance, and the voltage
drop across the capacitor’s ESR caused by the current
into and out of the capacitor. The worst-case voltage
ripple is:
where I
ceramic capacitors, the output voltage ripple is typically
dominated by V
temperature characteristics of the output capacitor must
also be considered. Note that all ceramic capacitors
typically have large temperature coefficients and bias
voltage coefficients. The actual capacitor value in the
circuit is typically significantly less than the stated value.
The input capacitor reduces the current peaks drawn
from the input supply and reduces noise injection into
the IC. A 10μF ceramic capacitor is recommended for
the Typical Applications Circuit/Functional Diagram
because of the high-source impedance seen in typical
lab setups. Actual applications usually have much
lower source impedance since the step-up regulator
often runs directly from a battery. Typically, the input
capacitance can be reduced below 10μF.
A bootstrap circuit that uses an external flying capaci-
tor between LX and BST provides the supply voltage
for the internal n-channel MOSFET driver. A 0.1μF or
larger ceramic capacitor provides sufficient current for
the internal MOSFET driver supply.
The MAX9738 operates with a standard 2.2μH inductor
for the entire range of supply voltages and load cur-
rents. The inductor must have a saturation (incremen-
tal) current (I
current. Choose an inductor that has a higher I
ing than the given FET Current Limit (Transient) specifi-
cation in the Electrical Characteristics table.
Temperature characteristics of the inductor’s saturation
current must also be considered.
I
Class G Amplifier with
V
V
V
L_RIPPLE
VSS_RIPPLE
VSS_RIPPLE(C)
VSS_RIPPLE(ESR)
L_RIPPLE
=
SAT
V
BAT
=
L
1
) rating greater than the peak switching
V
VSS_RIPPLE(C)
=
VSS_RIPPLE(C)
is the inductor ripple current. For
×
I
=
L_RIPPLE 2
2 C
t
I
L_RIPPLE(ESR)
FON
×
1
Boost Flying Capacitor (C3)
×
Input Filter Capacitor (C2)
V
×
SS
. The voltage rating and
L
+
1
V
×
VSS_RIPPLE(ESR)
×
Inductor Selection
t
FON
R
ESR
and
where
SAT
rat-
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