MP7751 – 26V, 2X20W STEREO BTL FIX FREQUENCY CLASS D AUDIO AMPLIFIER

MP7751 Rev. 1.0

www.MonolithicPower.com

13

5/23/2014

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OPERATION

The MP7751 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

MP7751

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 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 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 MP7751 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 MP7751 EN input is an active high enable

control. To enable the MP7751, drive EN with a

2.0V or higher voltage. To disable the amplifier,

drive it below 0.4V. While the MP7751 is disabled,

the PVCC operating current is around 250μA and

the output driver MOSFETs are turned off.

Input signal Absence detect

The MP7751 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 MP7751 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.

MP7751 will then hold the output report and

normal operation for a delay time which can

be adjusted by the Capacitor value @ pin 14.

Then MP7751 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. MP7751 will then

hold the output report for a delay time which

can be adjusted by the Capacitor value @

pin 14. Then MP7751 will turn off the all

MOSFETs and pull low the input absence

output, until the input signal detected again.