MAX4295 Maxim, MAX4295 Datasheet - Page 15

• Manufacturer Part Number: MAX4295
• Description: Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers
• Manufacturer: Maxim

The inductor current rating should be higher than the
peak current for a given output power requirement and
should have relatively constant inductance over tem-
perature and frequency. Typically, an open-core induc-
tor is desirable since these types of inductors are more
linear. Toroidal inductors without an air gap are not rec-
ommended. Q-shielded inductors may be required if
the amplifier is placed in an EMI-sensitive system. The
series resistance of the inductors will reduce the atten-
uation of the switching frequency and reduce efficiency
due to the ripple current in the inductor.
The capacitors should have a voltage rating 2 to 3
times the maximum expected RMS voltage—allowing
for high peak voltages and transient spikes—and be
stable over-temperature. Good quality capacitors with
low equivalent series resistance (ESR) and equivalent
series inductance (ESL) are necessary to achieve opti-
mum performance. Low-ESR capacitors will decrease
power dissipation. High ESL will shift the cutoff frequen-
cy, and high ESR will reduce filter rolloff.
The MAX4295/MAX4297 can be used as either a BTL
or single-ended configured amplifier. The BTL configu-
ration offers several advantages over a single-ended
configuration. By driving the load differentially, the out-
put voltage swing is doubled and the output power is
quadrupled in comparison to a single-ended configura-
tion. Because the differential outputs are biased at half
supply, there is no DC voltage across the load, elimi-
nating the need for large DC blocking capacitors at the
output.
The MAX4295/MAX4297 can be configured as single-
ended amplifiers. In such a case, the load must be
capacitively coupled to the filter to block the half-sup-
ply DC voltage from the load. The unused output pin
Figure 5. MAX4295 Single-Ended Configuration
MAX4295
Bridge-Tied Load/Single-Ended
______________________________________________________________________________________
OUT+
OUT-
Mono/Stereo 2W Switch-Mode (Class-D)
1
16
L1a
C1
Filter Components
Configuration
C
R
c
L
Audio Power Amplifiers
Figure 7. Headphone Application Circuit
must also be left open (Figure 5). Do not connect the
unused output pin to ground.
The MAX4295/MAX4297 can be used to drive a set of
headphones. A typical 3-wire headphone plug consists
of a tip, ring, and sleeve. The tip and ring are signal
carriers, while the sleeve is the ground connection
(Figure 6). Figure 7 shows the MAX4297 configured to
drive a set of headphones. The OUT+L and OUT+R
pins are connected to the tip and ring and deliver the
signal to the headphone jack, while the OUT-L and
OUT-R pins remain unconnected. The ground connec-
tion in the jack should be connected to the same
ground plane as the output filter.
The MAX4295/MAX4297 exhibit typical THD plus noise
of <1% for input frequencies <10kHz. The PWM fre-
quency affects THD performance. THD can be reduced
by limiting the input bandwidth through the input high-
pass filter, choosing the lowest f
fully selecting the output filter and its components.
Distortion caused by supply ripple due to H-bridge
switching can be reduced through proper bypassing of
PV
POSCAP capacitor to PGND and a 1µF ceramic capac-
itor to GND at each PV
1µF capacitor close to the PV
Figure 6. Typical 3-Wire Headphone Plug
CC
MAX4297
. For optimal performance, a 330µF, low-ESR
Bypassing and Layout Considerations
(LEFT)
TIP
OUT+R
OUT-R
OUT+L
OUT-L
(RIGHT)
RING
17
5
20
8
SLEEVE
(GND)
L1
L2
Total Harmonic Distortion
CC
Headphone Applications
C2
C1
input is suggested. Place the
a
a
CC
OSC
C
pin. Bypass V
C
C
C
possible, and care-
HEADPHONE JACK
LEFT
RIGHT
CC
GND
with
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