TAS5518 datasheet(49/103 Pages) TI

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TAS5518 Controls and Status

SLES115 — August 2004

TAS5518

2.3.6 Volume and Mute Update Rate

The TAS5518 has fixed soft volume and mute ramp durations. The ramps are linear. The soft volume and mute

ramp rates are adjustable by programming the I2C register 0xD0 for the appropriate number of steps to be

512, 1024, or 2048. The update is performed at a fixed rate regardless of the sample rate.

•

In normal speed, the update rate is 1 step every 4 / Fs seconds.

•

In double speed, the update is 1 step every 8 / Fs seconds.

•

In quad speed, the update is 1 step every 16 / Fs seconds.

Because of processor loading, the update rate can increase for some increments by +1/Fs to +3/Fs. However,

the variance of the total time to go from +18 dB to mute is less than 25%.

Table 2−8. Volume Ramp Rates in ms

NUMBER OF STEPS

SAMPLE RATE (KHZ)

NUMBER OF STEPS

44.1, 88.2, 176.4

32, 48, 96, 192

512

46.44 ms

42.67 ms

1024

92.88 ms

85.33 ms

2048

185.76 ms

170.67 ms

2.3.7 Modulation Index Limit

PWM modulation is a linear function of the audio signal. When the audio signal is 0, the PWM modulation is

50%. When the audio signal increases towards full scale, the PWM modulation increases towards 100%. For

negative signals, the PWM modulations fall below 50% towards 0%.

However, there is a limit to the maximum modulation possible. During the off-time period, the power stage

connected to the TAS5518 output needs to get ready for he next on-time period. The maximum possible

modulation is then set by the power stage requirements. All Texas Instruments power stages needs maximum

modulation to be 97.7%. This is also the default setting of the TAS5518. Default settings can be changed in

the Modulation Index Register (0x16).

Note that no change should be made to this register when using Texas Instruments power stages.

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