MAX4295 查看數據表（PDF） - Maxim Integrated
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MAX4295 Datasheet PDF : 18 Pages
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Mono/Stereo 2W Switch-Mode (Class-D)
Audio Power Amplifiers
Filter Components
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.
Bridge-Tied Load/Single-Ended
Configuration
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-
L1a
Cc
OUT+ 1
C1
MAX4295
RL
OUT- 16
Figure 5. MAX4295 Single-Ended Configuration
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
TIP RING SLEEVE
(LEFT) (RIGHT) (GND)
Figure 6. Typical 3-Wire Headphone Plug
L1
CC
OUT+L 5
OUT-L 20
C1a
MAX4297
L2
OUT+R 8
CC
OUT-R 17
C2a
HEADPHONE JACK
LEFT
GND
RIGHT
Figure 7. Headphone Application Circuit
must also be left open (Figure 5). Do not connect the
unused output pin to ground.
Headphone Applications
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.
Total Harmonic Distortion
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 fOSC possible, and care-
fully selecting the output filter and its components.
Bypassing and Layout Considerations
Distortion caused by supply ripple due to H-bridge
switching can be reduced through proper bypassing of
PVCC. For optimal performance, a 330µF, low-ESR
POSCAP capacitor to PGND and a 1µF ceramic capac-
itor to GND at each PVCC input is suggested. Place the
1µF capacitor close to the PVCC pin. Bypass VCC with
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