MP7742 – 2 x 15W CLASS D STEREO SINGLE ENDED AUDIO AMPLIFIER

MP7742 Rev. 0.91

www.MonolithicPower.com

10

1/25/2010

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2010 MPS. All Rights Reserved.

close to pins 12 and 14 as possible.

for the switching power stage. To prevent

overstressing of the MP7742 and excessive

pins 18 (VDD1) and 20 (PGND1) as possible

(VDD2) and 15 (PGND2) as possible.

Timing Capacitors

switching frequencies and are typically on

to pins 2 and 3 as possible to reduce

as close to pins 7 and 8 as possible.

Reference Bypass Capacitors

the

½

IC as possible to improve power supply

rejection and reduce distortion and noise

at the output.

Output Catch Diodes (optional components)

dead-time while the MOSFET switches are

off

and

provide

the

short

circuit

protection. Place the diodes as close to

the MP7742 as possible if these diodes are

needed.

2)

The

Inductor-Capacitor

(LC)

filter

converts the pulse train at SW to the

output voltage that drives the speaker.

Please keep the filter capacitor close to

the inductor.

3)

When

laying

out

the

PCB,

use

two

separate

ground

planes,

analog

ground

(AGND)

and

power

ground

(PGND),

and

connect the two grounds together at a

single

point

(usually

around

the

bulk

bypass

capacitor)

to

prevent

noise

injection

into

the

amplifier

input

to

reduce distortion.

4)

Keep

the

sensitive

feedback

signal

trace on the input side and shield the

trace with the AGND plane. Make sure that

any traces carrying the switch node (SW)

voltages are separated far from any input

signal traces. If it is required to run

the SW trace near the input, shield the

input with a ground plane between the

traces. For multiple channel applications,

make sure that each channel is physically

separated to prevent crosstalk. Make sure

that

all

inductors

used

on

a

single

circuit board have the same orientation.

Also, make sure that the power supply is

routed from the source to each channel

individually, not serially. This prevents

channel-to-channel

coupling

through

the

power supply input.

Electro-Magnetic Interference (EMI)

Considerations

Due to the switching nature of the Class D

amplifier, care must be taken to minimize the

effects of electromagnetic interference from the

amplifier. However, with proper component

selection and careful attention to circuit layout,

the effects of the EMI due to the amplifier

switching can be minimized.

The power inductors are a potential source of

radiated

emissions.

For

the

best

EMI

performance, use toroidal inductors, since the

magnetic field is well contained inside the core.

However toroidal inductors can be expensive to

wind. For a more economical solution, use

shielded gapped ferrite or shielded ferrite

bobbin core inductors. These inductors typically

do not contain the field as well toroidal

inductors, but usually can achieve a better

balance of good EMI performance with low cost.

The size of high-current loops that carry rapidly

changing currents needs to be minimized. To

capacitors are as close to the MP7742 as

possible.