MP7758

– 18V, 2x15W, STEREO BTL, INDUCTORLESS CLASS-D AUDIO AMPLIFIER

MP7758 Rev. 1.0

www.MonolithicPower.com

14

12/3/2020

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© 2020 MPS. All Rights Reserved.

OPERATION

The MP7758 is a fully integrated class-D stereo

BTL audio amplifier. The switching class-D

output

stage

provides

reduced

power

dissipation when compared to class-A, class-B

or class-A/B amplifiers, while maintaining high

fidelity and low distortion.

The amplifier has fully differential outputs and

inputs. The differential input minimizes common

mode noise (any noise that appears on both

input lines of the channel). The MP7758 can

also be used with a single-ended input.

The

MP7758

includes

eight

high-power

MOSFETs. For each half-bridge channel, the

output

driver

stage

uses

two

N-channel

MOSFETs to deliver the pulses to the magnetic

bead and capacitor output filter. This process

drives the load.

To fully enhance the high-side MOSFET (HS-

FET), the gate is driven to a voltage above the

source via the bootstrap capacitor placed

between the OUTxx and BSTxx pins. While the

output is driven low, the bootstrap capacitor is

charged from a power supply through an

internal circuit.

The gate of the HS-FET is driven high from the

voltage at the bootstrap supply, forcing the

MOSFET gate to a voltage above the power

supply voltage. This allows the MOSFET to fully

turn on, reducing power loss in the amplifier.

The gain of the MP7758 is set by the input

terminals (GAIN0 and GAIN1). The actual gain

settings are controlled by the ratios of the input

and feedback resistors

Enable (EN) Function

The MP7758 EN input is an active high enable

control pin. To enable the MP7758, drive the

EN pin to 2.0V or higher. To disable the

amplifier, drive EN below 0.4V. While the

MP7758 is disabled, the PVCC operating

current is about 250

μA, and the output driver

MOSFETs are turned off.

Absent Input Signal Detection

The MP7758 includes an internal circuit that

automatically shuts down the system after

detecting the absence of an audio signal. This

feature is used for energy-using products and

battery-operated applications.

The MP7758 includes a delay circuit that allows

the IC to hold the flag after the absence of the

audio signal. This holding time can be adjusted

with an external capacitor. Two absent input

scenarios are described in further detail below:



The input absence flag is initially high at

start-up. After the device is enabled, the

internal circuit starts to detect the input

signal. The MP7758 holds the output report

and normal operation for a delay time. This

time can be adjusted by the CAP_D

capacitor. Then the MP7758 turns off all

the MOSFETs. The input absence output is

pulled low until the input signal is detected

again (see Figure 2).

EN

Audio

Signal Input

InAbsence

Output

Enable

No Input Signal Detected

Delay Time

SW

PVCC

Start-

Up

Signal

Detected

Figure 2: Enable On (No Signal Detected)



The input absence flag output stays high or

is pulled high when an input signal is

detected. The delay circuit is only activated

when the input signal is absent. The

MP7758 holds the output report for a delay

time that can be adjusted by the CAP_D

capacitor. Then the MP7758 turns off the

all MOSFETs. The input absence output is

pulled low until the input signal is detected

again (see Figure 3).