TAS5548 datasheet(46/120 Pages) TI

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TAS5548

SLES270 – NOVEMBER 2012

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6.2

Programming Energy Manager

Energy Manager related registers are 0xBA to 0xBE. 0xB2 is a 16 byte averaging filter (alpha filter) for

both satellite and sub channel. The scaling coefficients are 0xB3 to 0xBA that multiplies energy of each

channel with a scaling factor. The threshold registers are (0xBB, 0xBC, 0xBD and 0xBE) and 0x10 for the

results register.

Table 6-1. Energy Manager Status Register (x10)

FUNCTION

–

0/1

Energy below the low threshold for satellite channels

–

0/1

–

Energy above the high threshold for satellite channels

–

0/1

–

Energy below the low threshold for sub-woofer

channel

0/1

–

Energy above the high threshold for sub-woofer

channels

So provision to read the whole byte and a way to clear the 4 LSB’s (one by one)

6.3

AM Avoidance Strategies

6.3.1

Frequency Scaling AM Avoidance

The AM avoidance strategy exploits the presence of the ASRC. The APLL output frequency is directly

varied by varying the multiplier ratio in the PLL loop. The dividers to generate clocks from the APLL are

fixed at their nominal division factor, so the result is that the internal sampling rate is changing accordingly.

The ASRC will adapt with this changing output rate (the internal sampling rate) and convert the incoming

sampling rates to this rate accordingly. The rest of the circuit does not change and operates normally, but

since the APLL output frequency is varied while the clock dividers are fixed, the PWM carrier frequency

becomes varied also, which is the goal of this AM avoidance strategy.

This shift in processing rate will effect time-domain digital processing, such as the EQ's and DRC's decay

values by the value in Freq_Error below.

Table 6-2. APLL/DAP/ASRC Clock Frequencies with New AM Avoidance Strategy

Input

Prescal

Feedba

Internal

# cycles

ASRC

Freq_Erro

Mode

XTAL

DCLK

DAP CLK

PWM rate

per FS

CLK

Normal

8 - 192k

12288

196608

131072

1365.33

98304

384

0.00%

AM#1

8 - 192k

12288

190464

126976

1365.33

95232

372

-3.13%

AM#2

8 - 192k

12288

184320

12288

1365.33

92160

360

-6.25%

AM#3

8 - 192k

12288

178176

118784

1365.33

89088

348

-9.38%

AM#4

8 - 192k

12288

172032

114688

1365.33

86016

336

-12.50%

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