TAS5414A datasheet(17/48 Pages) TI

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DESCRIPTION OF OPERATION

OVERVIEW

Preamplifier

Pulse-Width Modulator (PWM)

Gate Drive

TAS5414A, TAS5424A

SLOS535A – JULY 2007 – REVISED FEBRUARY 2008

The TAS5414A and TAS5424A are single-chip, four-channel, analog-input audio amplifiers for use in the

automotive environment. The design uses an ultra-efficient class-D technology developed by Texas Instruments,

but with changes needed by the automotive industry. This technology allows for reduced power consumption,

reduced heat, and reduced peak currents in the electrical system. The TAS5414A and TAS5424A realize an

audio sound system design with smaller size and lower weight than traditional class-AB solutions.

The TAS5414A and TAS5424A are composed of eight elements:

• Preamplifier

• PWM

• Gate drive

• Power FETs

• Diagnostics

• Protection

• Power supply

• I2C serial communication bus

The preamplifier of the TAS5414A and TAS5424A is a high-input-impedance, low-noise, low-offset-voltage input

stage with adjustable gain. The high input impedance of the TAS5414A and TAS5424A allows the use of

low-cost 1-

µF input capacitors while still achieving extended low-frequency response. The preamplifier is

separation. Also included in the preamp are:

1. Mute Pop-and-Click Control—An audio input signal is reshaped and amplified as a step when a mute is

applied at the crest or trough of the signal. Such a step is perceived as a loud click. This is avoided in the

TAS5414A and TAS5424A by ramping the gain gradually when a mute or play command is received.

Another form of click and pop can be caused by the start or stopping of switching in a class-D amplifier. The

TAS5414A and TAS5424A incorporate a patented method to reduce the pop energy during the switching

startup and shutdown sequence. Fault conditions require rapid protection response by the TAS5414A and

the TAS5424A, which do not have time to ramp the gain down in a pop-free manner. The device transitions

into Hi-Z mode when an OV, UV, OC, OT, or DC fault is encountered. Also, activation of the STANDBY pin

may not be pop-free.

2. Gain Control—The four gain settings are set in the preamplifier via I2C control registers. The gain is set

outside of the global feedback resistors of the TAS5414A and the TAS5424A, thus allowing for stability in the

system under all load conditions and gain settings.

3. DC Offset Reduction Circuitry—Circuitry has been incorporated to reduce the dc offset. DC offset in

high-gain amplifiers can produce audible clicks and pops when the amplifier is started or stopped. The offset

reduction circuitry can be disabled or enabled via I2C.

The PWM converts the analog signal from the preamplifier into a switched signal of varying duty cycle. This is

the critical stage that defines the class-D architecture. In the TAS5414A and TAS5424A, the modulator is an

advanced design with high bandwidth, low noise, low distortion, excellent stability, and full 0–100% modulation

capability. The patented PWM uses clipping recovery circuitry to eliminate the deep saturation characteristic of

PWMs when the input signal exceeds the modulator waveform.

The gate driver accepts the low-voltage PWM signal and level shifts it to drive a high-current, full-bridge, power

FET stage. The TAS5414A and TAS5424A use patent-pending techniques to avoid shoot-through and are

optimized for EMI and audio performance.

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Product Folder Link(s): TAS5414A TAS5424A

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