MP7741 – 10W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER

MP7741 Rev. 1.0

www.MonolithicPower.com

8

2/17/2011

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© 2011 MPS. All Rights Reserved.

OPERATION

The MP7741 is a single-ended Class D audio

amplifier. It uses the Monolithic Power Systems

convert the audio input signal into pulses.

These pulses drive an internal high-current

output stage and, when filtered through an

external inductor-capacitor filter, reproduce the

input 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, B or A/B amplifiers

while

maintaining

high

fidelity

and

low

distortion.

The amplifier uses differential input to the

modulator. PIN is the positive input and NIN is

the negative input. PIN is set to half the DC

internal circuit, so the common mode voltage of

the input NIN should be set to half the DC

The amplifier voltage gain is set by the

equation:

IN

FB

R

R

AV

−

=

The output driver stage uses two 250mΩ

N-Channel MOSFETs to deliver the pulses to

the LC output filter which in turn drives the load.

To fully enhance the high-side MOSFET, the

gate is driven to a voltage higher than the

source by the bootstrap capacitor between SW

and BS. While the output is driven low, the

an internal circuit on the MP7741. The gate of

the high-side MOSFET is driven high from the

voltage at BS, forcing the MOSFET gate to a

MOSFET to fully turn on, reducing power loss in

the amplifier.

Pop Elimination

pass only AC signals to the load. To insure that

the amplifier passes low frequency signals, the

However, when EN is asserted, the capacitor

charges over a long period and in a normal

amplifier can result in a turn on and turn off

“pop.”

The MP7741 integrates a source current

function to charge the AC coupling capacitor

Cout and Cin at the start up moment. The start

up source current slew rate is adjustable by

selecting

different

capacitance

of

timer

capacitor Ctimer. The larger the Ctimer

capacitance is, the smaller the start up current

slew rate is. The recommended 2.2µF capacitor

Ctimer results in a start up current slew rate of

approximately 20mA/350ms which would help

to minimize the turn on pop.

After driving EN pin low, output SW will be set

to high impedance immediately which would

help to eliminate the turn off pop.

Short Circuit/Overload Protection

The MP7741 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 3A short circuit

current limit, both MOSFETs are turned off. The

MP7741 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 MP7741 EN input is an active high enable

control. To enable the MP7741, drive EN with a

2.0V or greater voltage. To disable the

amplifier, drive it below 0.4V. While the MP7741

is disabled, the VDD operating current is less

than 100µA and the output driver MOSFETs are

turned off.

Programmable UVP

MP7741 integrate programmable UVP function,

which can be used to shutdown the MP7741 to

escape the pop, by controlling the UVP node

voltage. The corresponding circuit is shown in

the followed figure 2. If the UVP pin is NC, the

default VDD shutdown voltage is 8.4V since

there

is

internal

voltage

divided

circuit.