Datasheet

TAS5548

SLES270 –NOVEMBER 2012

www.ti.com

4 PWM

4.1 PWM Features

The TAS5548 has eight channels of high-performance digital PWM modulators that are designed to drive

switching output stages (back ends) in both single-ended (SE) and bridge-tied-load (BTL) configurations.

The device uses noise-shaping and sophisticated, error-correction algorithms to achieve high power

efficiency and high-performance digital audio reproduction. The TAS5548 uses an AD/BD/Ternary PWM

modulation scheme combined with a fourth-order noise shaper to provide a >105-dB SNR from 20 Hz to

20 kHz.

The PWM section accepts 32-bit PCM data from the DAP and outputs eight PWM audio output channels

configurable as either:

• Six channels to drive power stages and two channels to drive a differential-input active filter to provide

a separately controllable stereo lineout

• Eight channels to drive power stages

The PWM section provides a headphone PWM output to drive an external differential amplifier like the

TPA6139A2. The headphone circuit uses the PWM modulator for channels 1 and 2. The headphone does

not operate while the six or eight back-end drive channels are operating. The headphone is enabled via a

headphone-select terminal.

The PWM section also contains the power-supply volume control (PSVC) PWM.

The interpolator, noise shaper, and PWM sections provide a PWM output with the following features:

• Up to 8× oversampling

– 4× at f

= 88.2 kHz, 96 kHz

– 2× at f

= 176.4 kHz, 192 kHz

• Fourth-order noise shaping

• 105-dB dynamic range 0–20 kHz (TAS5548 + TAS5614 system measured at speaker terminals)

• THD < 0.01%

• Adjustable modulation limit of 87.4% to 99.2%

• 3.3-V digital signal

4.1.1 DC Blocking (High-Pass Filter Enable/Disable)

Each input channel incorporates a first-order, digital, high-pass filter to block potential dc components. The

filter –3-dB point is approximately 2-Hz at the 96-kHz sampling rate. The high-pass filter can be enabled

and disabled via the I

C system control register 1 (0x03 bit D7). The default setting is 1 (high-pass filter

enabled).

4.1.2 AM Interference Avoidance

Digital amplifiers can degrade AM reception as a result of their RF emissions. Texas Instruments' patented

AM interference-avoidance circuit provides a flexible system solution for a wide variety of digital audio

architectures. During AM reception, the TAS5548 adjusts the radiated emissions to provide an emission-

clear zone for the tuned AM frequency. The inputs to the TAS5548 for this operation are the tuned AM

frequency, the IF frequency, and the sample rate. This PWM rate modification is done by modifying the

output rate of the Sample Rate Converter, and the following DSP and PWM modulator.

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