TAS5518C datasheet(39/103 Pages) TI1

39 / 103 page

2.12.1 DC Blocking (High-Pass Filter 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)

TAS5518C

8-Channel Digital Audio PWM Processor

www.ti.com

SLES238A – SEPTEMBER 2008 – REVISED JULY 2009

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 f

S = 44.1 kHz, 48 kHz, 32 kHz, 38 kHz

–

× at f

S = 88.2 kHz, 96 kHz

–

× at f

S = 176.4 kHz, 192 kHz

• Fifth-order noise shaping

• 110-dB dynamic range 0–20 kHz (TAS5518C + 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 system control register 1 (0x03 bit D7). The default setting is 1

(high-pass filter enabled).

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 TAS5518C 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 PSVC 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. Note that if the PVSC function is not used, the volume biquad

should be all-pass (default).

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