Datasheet

Calculation of Output Signal Level of TAS5716 Feedback Power Stage
I
2
C SERIAL-CONTROL COMMAND CHARACTERISTICS
TAS5716
SLOS569 – JANUARY 2009 ............................................................................................................................................................................................... www.ti.com
(Gain Is Independent of PVCC)
The gain of the TAS5716 is the total digital gain of the controller multiplied by the gain of the power stage.
For a half-bridge channel of the TAS5716 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
= Audio voltage level at the output of the power stage = 13 × modulation level
For the TAS5716 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 TAS5716 can now be calculated.
V
RMS
= digital FFS × digital gain × maximum modulation level × 13
With the modulation limit set at the default level of 97.7%, this becomes:
V
RMS
= digital FFS × digital gain × 12.4 (Single-ended)
V
RMS
= digital FFS × digital gain × 24.8 (BTL)
Example: Input = – 20 dbFS; volume = 0 dB; biquads = ALL PASS; modulation index = 97.7%; mode = BTL
Output V
RMS
= 24.8 × 0.1 × 1 = 2.48 V
The DAP has two groups of I
2
C commands. One set is commands that are designed specifically to be operated
while audio is streaming and that have built-in mechanisms to prevent noise, clicks, and pops. The other set
does not have this built-in protection.
Commands that are designed to be adjusted while audio is streaming:
• Master volume
• Master mute
• Individual channel volume
• Individual channel mute
Commands that are normally issued as part of initialization:
• Serial-data interface format
• De-emphasis
• Sample-rate conversion
• Input multiplexer
• Output multiplexer
• Biquads
• Channel-6 multiplexer-2
• Channel delay
• Enable/disable dc blocking
• Hard/soft unmute from clock error
• Enable/disable headphone outputs
Start-up sequence for correct device operation
This sequence must be followed to ensure proper operation.
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Product Folder Link(s): TAS5716