MP1720 – 2.7W LOW EMI HIGH EFFICIENCY MONO CLASS-D AUDIO AMPLIFIER

MP1720 Rev. 1.01

www.MonolithicPower.com

11

8/9/2012

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APPLICATION INFORMATION

COMPONENT SELECTION

The MP1720 uses a minimum number of external

components to complete a fully bridged Class D

audio amplifier. Use the following sections to

customize the amplifier for your particular

application.

The MP1720 is a mono BTL Class-D amplifier

with differential outputs and inputs. If the input

signal is not biased within the recommended

common-mode input range or if using a single-

ended source, the input coupling capacitors are

used to pass only the AC audio signal to the

input of the amplifier as a high pass filter. Choose

an input coupling capacitor such that the corner

frequency. The formula for the corner frequency

is:

IN

IN

IN

1

f

2R C





(2)

handsets usually can’t respond well to low

frequencies, so for this application the corner

frequency can be set to block the low frequencies.

The input coupling capacitance is calculated as:

IN

IN IN

1

C

2R f





(3)

If the corner frequency is within the audible band,

the capacitors should have a tolerance of ±10%

or better, because any mismatch in capacitance

causes an impedance mismatch at the corner

frequency and below.

Tantalum or aluminum electrolytic capacitor with

low-voltage coefficients is recommended, or the

largest package ceramics capacitor to minimize

voltage coefficient effects, for example X7R

dielectrics is better than Y5V or Z5U.

The class-D audio amplifier requires adequate

power supply decoupling to ensure the efficiency

is high and total harmonic distortion (THD+N) is

low. To carry the higher frequency transient

current, spikes, or digital hash on the line, a good

low

ESR ceramic capacitor is necessary. Place a 1μF

decoupling capacitor as close as possible to the

device VCC lead. It is very important for the

efficiency of the class-D amplifier, because any

resistance or inductance in the trace between the

capacitor and the device may cause a loss. A

10μF or greater capacitor placed near the audio

power amplifier would also help for filtering lower-

frequency noise