MP7705 – 12V, 2x5W/2x2.5W CLASS–D STEREO SINGLE ENDED AUDIO AMPLIFIER

MP7705 Rev. 1.1

www.MonolithicPower.com

8

9/18/2009

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PCB Layout

The circuit layout is critical for optimum

performance and low output distortion and

noise. Place the following components as close

to the MP7705 as possible:

the

switching

power

stage.

To

prevent

overstressing of the MP7705 and excessive

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

15 (PGND2) as possible.

Output Catch Diodes

the dead-time while the MOSFET switches are

off. Place the diodes as close to the MP7705 as

possible.

Timing Capacitors

switching frequencies and are typically on the

and 3 as possible to reduce distortion and noise.

as possible.

Reference Bypass Capacitors

possible to improve power supply rejection and

reduce distortion and noise at the output.

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 to prevent

noise injection into the amplifier input to reduce

distortion.

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 as 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 and the Schottky Catch diodes are

as close to the MP7705 as possible.

Nodes that carry rapidly changing voltages,

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.