MP7748 – 2X20W STEREO SINGLE ENDED CLASS D AUDIO AMPLIFIER

MP7748 Rev. 1.0

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15

1/28/2011

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to the MP7748 while blocking the DC voltage.

Choose an input coupling capacitor such that the

frequency. The corner frequency is calculated as:

IN

IN

IN

C

R

2

1

f

×

×

π

×

=

Timer capacitor

The start up source current slew rate is

adjustable by selecting different capacitance of

capacitance is, the smaller the start up current

which capacitance is larger than 312nF, so the

start up current slew rate would be smaller than

20mA/50ms which would help to eliminate the

turn on pop. The recommended 2.2µF capacitor

approximately 20mA/350ms.

Power Source

For maximum output power, the amplifier circuit

requires a regulated external power source to

supply the power to the amplifier. The higher the

power supply voltage, the more power can be

delivered to a given load resistance, however if

the power source voltage exceeds the maximum

voltage of 36V, the MP7748 may sustain

damage. The power supply rejection of the

MP7748 is excellent, however noise at the power

supply can get to the output, so care must be

taken to minimize power supply noise within the

pass-band frequencies. Bypass the power supply

with a large capacitor (typically aluminum

electrolytic) along with a smaller 1µF ceramic

PCB Layout

The circuit layout is critical for optimum

performance and low output distortion and noise.

It is highly recommended to duplicate EVB layout

for

optimum

performance.

If

change

is

necessary, please follow these guidelines and

take Figure 7 for references.

1) Place the following components as close to

the MP7748 as possible:

Bootstrap Cap

current to the internal high-side MOSFET. Place

pin and SW2 pins as possible.

Power Supply Bypass Cap

switching power stage. To prevent overstressing

of the MP7748 and excessive noise at the output,

VDD2 pins and PGND2 pins as possible.

Integral Capacitors

frequencies and are typically on the order of a

to the corresponding input as possible to reduce

close to pins 2 and 3 as possible at SE output

configuration.

Reference Bypass Capacitors For SE Output

When used with SE output, CR1 and CR2 is

needed to filter the ½ VDD reference voltages.

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. 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