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

MP7705 Rev. 1.1

www.MonolithicPower.com

5

9/18/2009

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© 2009 MPS. All Rights Reserved.

OPERATION

The MP7705 uses Monolithic Power Systems’

convert the audio input signal into pulses of

power that, when filtered through an external

inductor-capacitor filter, reproduce the amplified

signal across the load. Because of the

switching

Class–D

output

stage,

power

dissipation in the amplifier is drastically reduced

when compared to Class A or A/B amplifiers

while providing high fidelity and low distortion.

The voltage gain is set by the combination of

IN

FB

V

R

R

A

−

=

The

MP7705

includes

four

high-power

MOSFETS wherein for each channel the output

driver stage uses two 250mΩ N-Channel

MOSFETs to deliver the pulses to the LC output

filter that in turn drives the load. To fully

enhance the high-side MOSFET, the gate is

bootstrap capacitor between SW and BS. While

the output is driven low, the bootstrap capacitor

MOSFET is driven high from the voltage at BS,

forcing the MOSFET gate to a voltage higher

on, reducing power loss in the amplifier.

Pop Elimination

signal and pass only the AC signals to the load.

To insure that the amplifier passes low

frequency signals, the capacitor values need to

need to be charged up to the DC operating

MP7705 includes special integrated circuitry

that carefully controls the pre-charging of these

capacitors, eliminating the turn-on and turn-off

pop normally associated with the charging of

the AC coupling capacitors.

Short Circuit/Overload Protection

The MP7705 has internal overload and short

circuit protection. The currents in both the

high-side

and

low-side

MOSFETs

are

measured and if the current exceeds the 4.0A

short circuit current limit, both MOSFETs are

turned off. The MP7705 then restarts with the

same power up sequence that is used for

normal starting to prevent a pop from occurring

after a short circuit condition is removed.

Mute/Enable Function

The MP7705 EN inputs are active high enable

controls. To enable the MP7705, drive EN with

a 2.0V or higher voltage. To disable the

amplifier, drive EN below 0.4V. While the

is less than 10μA and the output driver

MOSFETs are turned off. The MP7705 requires

approximately 500ms from the time that EN is

asserted (driven high) to when the amplifier

begins normal operation.