MP7752 – 18V, 2X15W STEREO FIX FREQUENCY INDUCTORLESS BTL CLASS D AUDIO AMPLIFIER

MP7752 Rev. 1.01

www.MonolithicPower.com

14

5/27/2016

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OPERATION

The MP7752 is a fully integrated Class D stereo

BTL audio amplifier. 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 has fully differential outputs and

inputs. The differential input is useful to minimize

the common-mode noise (any noise that appears

on both input lines of the channel). This device

can still be used with a single-ended input.

The

MP7752

includes

eight

high-power

MOSFETs wherein 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 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 OUTxx and BSTxx pins. While the

output is driven low, the bootstrap capacitor is

charged from power supply through an internal

circuit. The gate of the high-side MOSFET is

driven high from the voltage at Bootstrap Supply,

forcing the MOSFET gate to a voltage higher

than power supply voltage and allowing the

MOSFET to fully turn on, reducing power loss in

the amplifier.

The gain of the MP7752 is set by the input

terminals, GAIN0 and GAIN1. The actual gain

settings are controlled by ratios of the input and

feedback resistors

Enable Function

The MP7752 EN input is an active high enable

control. To enable the MP7752, drive EN with a

2.0V or higher voltage. To disable the amplifier,

drive it below 0.4V. While the MP7752 is disabled,

the PVCC operating current is around 250μA and

the output driver MOSFETs are turned off.

Input signal Absence detect

The MP7752 includes an internal circuit which

allows the system automatic shutdown after the

absence of the audio signal. This feature is used

for energy-using products and for battery

operated applications.

The MP7752 includes a delay circuit which

allows the IC continues to hold the flag after the

absence of the audio signal. This holding time

can be adjusted with external capacitor.

1. The input absence flag will be high initially

when power on. After device enabled, the

internal circuit start to detect the input signal.

MP7752 will then hold the output report and

normal operation for a delay time which can

be adjusted by the Capacitor value @ pin 14.

Then MP7752 will turn off the all MOSFETs

and pull low the input absence output, until

the input signal detected again.

Figure 1a: enable on with no signal detected

2. The input absence flag output will be or

maintain high when input signal is detected.

The delay circuit will only be activated when

the input signal absence. MP7752 will then

hold the output report for a delay time which

can be adjusted by the Capacitor value @

pin 14. Then MP7752 will turn off the all

MOSFETs and pull low the input absence

output, until the input signal detected again.