MP7745 – 2 x 19W CLASS D STEREO SINGLE ENDED AUDIO AMPLIFIER

MP7745 Rev. 0.9

www.MonolithicPower.com

11

5/11/2009

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the

switching

power

stage.

To

prevent

overstressing of the MP7745 and excessive

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

15 (PGND2) as possible.

Timing Capacitors

switching frequencies and are typically on the

and 3 as possible to reduce distortion and

and 8 as possible.

Reference Bypass Capacitors

to improve power supply rejection and reduce

distortion and noise at the output.

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 MP7745 as

possible.

Nodes that carry rapidly changing voltage, such

as SW, need to be made as small as possible.

If sensitive traces run near a trace connected to

SW, place a ground shield between the traces.