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產(chǎn)品名稱：AXPA47576 2x45W MOSFET Dual Bridge 24V Audio Power Amplifier
型號： AXPA47576
產(chǎn)片介紹：The AXPA47576 is a dual bridge audio Class AB power amplifier with MOSFET output power stages It has been specifically designed for 24V power supply system making it compatible with truck bus applications The feedback topology allows excellent distortion performance and the integrated buffer minimizes the need for external components

┄┄┄詳細介紹┄┄┄

Description

The AXPA47576 is a dual bridge audio Class AB power amplifier with MOSFET output power stages. It

has been specifically designed for 24V power supply system making it compatible with truck/bus

applications. The feedback topology allows excellent distortion performance and the integrated buffer

minimizes the need for external components. The fully complementary P-channel/N-channel output

structure allows rail-to-rail output voltage swing minimizing saturation losses. The AXPA47576 integrates

a DC offset detector, a clipping detector, and a diagnostic output.

Features

? 24V battery operation

? High output power capability

– 2 x 45W/4Ω Max @ 28V, Sq Wave

– 2 x 25W/4Ω @ 28V, 1kHz; 10% THD

? Minimized external components`

– No decoupling capacitors

– No bootstrap capacitor

– No external compensation

– Internally fixed gain

? Standby function

? Mute function

? Diagnostic pin for:

– Clip detector (THD 2%)

– Short circuit detection

– Thermal protection

? Output DC offset detection

? Protections:

– 60V load dump

– Overrating chip temperature

– Output short circuit protection (to GND, VCC and across the load)

– ESD

1 Block Diagram and Application Circuit

2 Pin Description

2.1 Pin Names

2.2 Pin Functions

3 Electrical Specifications

3.1 Absolute Maximum Ratings

3.2 Thermal Data

3.3 Electrical Characteristics

4 Principle of Operation

The AXPA47576 is an innovative stereo audio amplifier meant for typical 24V battery vehicles.

The amplifier works in a single-ended configuration without the large decoupling capacitors on

the outputs normally required by the single-ended topology. Its principle of operation is depicted

in Figure 5.

Channel 1 is electrically inverting its input signal whereas channel 2 is not. If the speakers are

connected with the positive pole of speaker 2 connected to OUT2 and the negative pole of

speaker 1 connected to OUT1, then the two channels both behave as non-inverting. Speaker

1 and speaker 2 have one terminal in common and further connected to a half VCC (HVCC)

buffer.

If the signals at IN1 and IN2 are identical, then the voltage at OUT1 and OUT2 is identical in

magnitude but inverted (OUT1 = -OUT2), and the current flowing through speaker 1 is all

coming from speaker 2, with no current going into the HVCC buffer. If the signal at IN1 is not

identical to that at IN2, then the signal at the two outputs will not be identical either, and some

current will flow into or out of the HVCC buffer, keeping the voltage at HVCC constant.

This structure allows therefore the amplifier to operate in a single-ended configuration with no

need for decoupling capacitors.

Mathematically this can be expressed as:

VL1 = -G * Vin1

VL2 = +G * Vin2

IHVCC = Io1 + Io2 = VL1/RL + VL2/RL = G (Vin2 - Vin1) / RL

where VL1,2 is the voltage across speaker 1 or 2, G is the gain of the amplifiers and RL is the

load resistance (supposed identical for the two speakers).

In the common practice the two channels of the amplifier are used for the left and the right

audio parts of the stereo signal, and therefore the two outputs are not identical. This means

that it is never mathematically true that all the current into one speaker comes from the other

speaker, so the HVCC buffer will always have to provide a certain amount of difference current.

Apart from the fact that the left and the right audio channels are not identical unless the

program is monophonic, other reasons why the HVCC buffer has to provide current are:

imbalance in the level of the L and the R channel, equalization-induced delay in one channel

compared to the other.

The current provided by the HVCC buffer leads to non-negligible power dissipation inside the

IC: this should be added to power dissipation the output stages 1 and 2. It is necessary to keep

this additional dissipation in mind when dimensioning the car radio heat sink.

5 Power Dissipation Computation

The instantaneous power dissipated by each output stage is given by the formula below:

PD1,2(t) = 1/RL |VL1,2(t)| (VCC/2 - |VL1,2(t)|)

with VL1,2(t) being the output signal on each of the two channels VL1,2(t) = G * Vin1,2(t).

If the two input signals are not identical, as seen in Section 4, a current IHVCC flows into or out

of the half VCC buffer, this current causes dissipation within the HVCC buffer given by:

PDHVCC(t) = VCC/(2RL) | VL2(t) - VL1(t) |

which is obviously 0 when the two channels have identical signals.

The total instantaneous power dissipation inside the AXPA47576 is therefore given by:

Pdtot(t) = PD1(t) + PD2(t) + PDHVCC(t)

The dimensioning of the heat sink of the system must take into consideration these three

components.

6 Functional Description

6.1 Diagnostics pins description

The AXPA47576 includes an offset detector pin and a clip detector/diagnostic pin.

DC offset detector is intended to avoid that an anomalous DC offset on the inputs of the

amplifier may be multiplied by the gain and result in a dangerous large offset on the outputs.

This may lead to speakers damage due to overheating.

The feature works with the amplifier unmuted and no signal at the inputs.

Moreover, there is a pin named CD/Diag: the behavior of this pin is showed on Figure 4.

Whenever a failure condition (between thermal warning, output waveform clipping, short circuit

to GND or VCC) is verified by the IC, the level of this pin goes true (low).

6.2 Thermal protections

Thermal protection function is triggered when junction temperature rises above the normal

operating range, thus avoiding chip damaging.

For behavior description, refer to Figure 4 and 6. When the temperature reaches thermal

warning (Tw = 140°C typ) the CD/Diag pin is driven low. Thermal foldback begins limiting the

audio input to the amplifier stage. This effectively limits the output power capability of the device,

thus reducing the temperature to acceptable levels without totally interrupting the operation of

the device. Thermal mute is temperature when -6dB output attenuation is reached (Tm = 160°C

typ).

The output power will decrease to the point at which thermal equilibrium is reached. Thermal

equilibrium will be reached when the reduction in output power reduces the dissipated power

so that the die temperature falls below the thermal foldback threshold.

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