MP7770 –2 X 45W STEREO SE OR 90W MONO BTL CLASS D AUDIO AMPLIFIER

MP7770 Rev.1.0

www.MonolithicPower.com

13

12/4/2012

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2012 MPS. All Rights Reserved.

OPERATION

The MP7770 is a Class D Audio Amplifier that

drives

stereo

speakers

in

single-ended

configuration or a mono speaker in bridge-tied-

load configuration. It uses MPS’s patented

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 against Class A, B or A/B

amplifiers, and maintains high fidelity with low

distortion.

REF1 and REF2 are the positive inputs of the

two amplifiers. They are set to half the DC

internal

circuit.

The

input

capacitor

decouples the AC signal at the input.

by the equation:

IN

FB

R

R

AV





Where:

The

MP7770

includes

four

high-power

MOSFETs; For each channel, the output driver

stage uses two 100mΩ N-channel MOSFETs to

deliver pulses to the LC output filter to drive the

load. To enhance the high-side MOSFET (HS-

FET), the gate is driven to a voltage higher than

the source by the bootstrap capacitor between

SW and BS. When the output is low, the

an internal circuit on the MP7770. The gate of

the HS-FET is driven high by the BST voltage,

forcing the MOSFET gate to a voltage higher

and reducing amplifier power loss.

Pop Elimination

When

used

in

a

single-ended

output

block the DC signal and pass the AC signals to

the load. To insure that the amplifier only

passes low-frequency signals, the time constant

high, the capacitor charges over a long period

and can result in turn-on/turn-off “pop” In typical

amplifiers.

The MP7770 integrates a source-current

function to charge the DC block capacitors

Two internally-generated currents flow to the

during start-up, which helps to eliminate turn-on

pop. The rising/falling slew rate of the SW node

band (means rise and falling gradually), can be

capacitance, the smaller the slew rate of the

After driving the EN pin low, the output SW

immediately switches to high impedance to

eliminate turn-off pop.

Short Circuit/Overload Protection and

Monitoring

The MP7770 is fully-protected against over-

current and thermal overload conditions as

explained below and \shown in Figure2.

Short Circuit/Overload Protection

The MP7770 has internal overload and short-

circuit protection. The currents in both the high-

side and low-side MOSFETs (LS-FETs) are

measured and if the current exceeds the short

circuit

current

limit

(typically

8A),

both

MOSFETs will be turned off for a fixed duration

(around 1ms) before resuming normal operation.

After the fixed duration and the short circuit

condition is removed, the MP7770 will restart

with the start-up sequence that is used for

normal starting to prevent a pop from occurring.