Mono, 2W, Switch-Mode (Class D)

Audio Power Amplifier

12

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C1

OUT+

OUT-

16

MAX4295

L1a

1

Figure 5. MAX4295 Single-Ended Configuration

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 can be used as either a BTL or single-

ended configured amplifier. The BTL configuration offers

several advantages over a single-ended configuration.

By driving the load differentially, the output voltage swing

is doubled and the output power is quadrupled in com-

parison to a single-ended configuration. Because the dif-

ferential outputs are biased at half supply, there is no DC

voltage across the load, eliminating the need for large

DC-blocking capacitors at the output.

The MAX4295 can be configured as a single-ended

amplifier. In such a case, the load must be capacitively

coupled to the filter to block the half-supply DC voltage

from the load. The unused output pin must also be left

open (Figure 5). Do not connect the unused output pin

to ground.

Total Harmonic Distortion

The MAX4295 exhibits typical THD+N of <1% for input

frequencies <10kHz. The PWM frequency affects THD

performance. THD can be reduced by limiting the input

bandwidth through the input highpass filter, choosing

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

POSCAP capacitor to PGND and a 1µF ceramic capac-

a 10µF capacitor in parallel with a 1µF capacitor to

GND. Ceramic capacitors are recommended due to

their low ESR.

Good PC board layout techniques optimize perfor-

mance by decreasing the amount of stray capacitance

at the amplifier’s inputs and outputs. To decrease stray

capacitance, minimize trace lengths by placing exter-

nal components as close as possible to the amplifier.

Surface-mount components are recommended.

The MAX4295 requires two separate ground planes to

prevent switching noise from the MOSFETs in the H-

bridge from coupling into the rest of the circuit. PGND,

the power ground, is utilized by the H-bridge and any

external output components, while GND is used by the

rest of the circuit. Connect the PGND and GND planes

at only one point, as close to the power supply as pos-

sible. Any external components associated with the

output of the MAX4295 must be connected to the

PGND plane where applicable. Use the Typical

Operating Circuit diagram as a reference. Refer to the

evaluation kit manual for suggested component values,

component suppliers, and layout.