TAS5708 datasheet(30/56 Pages) TI

30 / 56 page

APPLICATION INFORMATION

Calculation of Output Signal Level of TAS5708 Feedback Power Stage

TAS5708

SLOS570 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com

(Gain Is independent of PVCC)

The gain of the TAS5708 is the total digital gain of the controller multiplied by the gain of the power stage.

For a half-bridge channel of the TAS5708 power stage, the gain is simply:

Power stage gain = 13 × VRMS / Modulation Level

Modulation level = fraction of full-scale modulation of the PWM signal at the input of the power stage.

VRMS(SE) = Audio voltage level at the output of the power stage = 13 × Modulation Level

VRMS(BTL) = 2 × Audio voltage level at the output of the power stage = 26 × Modulation Level

For the TAS5708 controller, the gain is the programmed digital gain multiplied by a scaling factor, called the

maximum modulation level. The maximum modulation level is derived from the modulation limit programmed in

the controller, which limits duty cycle to a set number of percent above 0% and below 100%. Setting the

modulation limit to 97.7% (default) limits the duty cycle between 2.3% and 97.7%.

Controller gain = digital gain × maximum modulation level × (modulation level/digital FFS)

Digital FFS = digital input fraction of full scale

Modulation limit = 97.7%

Maximum modulation level = 2 × modulation limit – 1 = 0.954

The output signal level of the TAS5708 can now be calculated:

VRMS(SE) = digital FFS × digital gain × maximum modulation level × 13

VRMS(BTL) = 2 × VRMS(SE)

With the modulation limit set at the default level of 97.7%, this becomes:

VRMS (BTL) = digital FFS × digital gain × 24.8

Example: Input = –20 dbFS; volume = 0 dB; biquads = ALL PASS; modulation index = 97.7%; mode = BTL

Output VRMS (BTL) = 24.8 × 0.1 × 1 = 2.48 V.

Submit Documentation Feedback

Product Folder Link(s): TAS5708

TAS5708 データシート(PDF) 30 Page - Texas Instruments

TAS5708 データシート(HTML) 30 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

データシートダウンロード