Datasheet

APPLICATION INFORMATION
Calculation of Output Signal Level of TAS5710 Feedback Power Stage
TAS5710
SLOS605 – JANUARY 2009 ............................................................................................................................................................................................... www.ti.com
(Gain Is independent of PVCC)
The gain of the TAS5710 is the total digital gain of the controller multiplied by the gain of the power stage.
For a half-bridge channel of the TAS5710 power stage, the gain is simply:
Power stage gain = 13 × V
RMS
/ Modulation Level
Modulation level = fraction of full-scale modulation of the PWM signal at the input of the power stage.
V
RMS
(SE) = Audio voltage level at the output of the power stage = 13 × Modulation Level
V
RMS
(BTL) = 2 × Audio voltage level at the output of the power stage = 26 × Modulation Level
For the TAS5710 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 TAS5710 can now be calculated:
V
RMS(SE)
= digital FFS × digital gain × maximum modulation level × 13
V
RMS(BTL)
= 2 × V
RMS(SE)
With the modulation limit set at the default level of 97.7%, this becomes:
V
RMS
(BTL) = digital FFS × digital gain × 24.8
Example: Input = – 20 dbFS; volume = 0 dB; biquads = ALL PASS; modulation index = 97.7%; mode = BTL
Output V
RMS
(BTL) = 24.8 × 0.1 × 1 = 2.48 V.
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