TAS5508 datasheet(40/105 Pages) TI

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2.12.1 DC Blocking (High-Pass Enable/Disable)

2.12.2 De-Emphasis Filter

f – Frequency – kHz

3.18 (50

µs)

−10

10.6 (15

µs)

De-emphasis

M0015-01

2.12.3 Power-Supply Volume Control (PSVC)

TAS5508

8-Channel Digital Audio PWM Processor

SLES091D – FEBRUARY 2004 – REVISED JULY 2009

www.ti.com

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

–

＝ at FS = 44.1 kHz, 48 kHz, 32 kHz, 38 kHz

–

＝ at FS = 88.2 kHz, 96 kHz

–

＝ at FS = 176.4 kHz, 192 kHz

• Fifth-order noise shaping

• 100-dB dynamic range 0–20 kHz (TAS5508 + TAS5111 system measured at speaker terminals)

• THD < 0.01%

• Adjustable maximum modulation limit of 93.8% to 99.2%

• 3.3-V digital signal

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

filter –3-dB point is approximately 0.89-Hz at the 44.1-kHz sampling rate. The high-pass filter can be

enabled and disabled via the I2C interface.

For audio sources that have been pre-emphasized, a precision 50-

µs/15-µs de-emphasis filter is provided

to support the sampling rates of 32 kHz, 44.1 kHz, and 48 kHz. Figure 2-19 shows a graph of the

de-emphasis filtering characteristics. De-emphasis is set using two bits in the system control register.

Figure 2-19. De-Emphasis Filter Characteristics

The TAS5508 supports volume control both by conventional digital gain/attenuation and by a combination

of digital and analog gain/attenuation. Varying the H-bridge power-supply voltage performs the analog

volume control function. The benefits of using power-supply volume control (PSVC) are reduced idle

channel noise, improved signal resolution at low volumes, increased dynamic range, and reduced radio

frequency emissions at reduced power levels. The PSVC is enabled via I2C. When enabled, the PSCV

provides a PWM output that is filtered to provide a reference voltage for the power supply. The

power-supply adjustment range can be set for –12.04, –18.06, or –24.08 dB, to accommodate a range of

variable power-supply designs.

Figure 2-20 and Figure 2-21 show how power-supply and digital gains can be used together.

The volume biquad (0xCF) can be used to implement a low-pass filter in the digital volume control to

match the PSVC volume transfer function.

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