TAS2553_15 datasheet(19/58 Pages) TI

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VBAT

InflPt

VBAT

VLIM

InflPt

TAS2553

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SLAS978B – SEPTEMBER 2013 – REVISED FEBRUARY 2014

7.3.10 Battery Tracking AGC

The TAS2553 monitors battery voltage and the audio signal to automatically decrease gain when the battery

voltage is low and audio output power is high. This finds the optimal gain to maximize loudness and minimize

battery current, providing louder audio and preventing early shutdown at end-of-charge battery voltage levels.

This does not mean the battery tracking AGC automatically decreases amplifier gain when VBAT is below the

inflection point. Rather, gain is decreased only when the Class-D output voltage exceeds the limiter level.

Figure 29. VLIM versus Supply Voltage (VBAT)

When VBAT is greater than the inflection point, VLIM - the peak allowed output voltage - is set by the boost

voltage. The inflection point is set in Register 0x0B, Bits 7-0. The inflection point range is 3.0 V to 5.5 V,

adjustable in 17.33 mV steps.

When VBAT is less than the inflection point, the peak output voltage is controlled by the slope. Set the VLIM vs.

VBAT slope in Register 0x0C, Bits 7-0. This

ΔVLIM / ΔVBAT range is 1.2 V/V to 10.75 V/V and is adjustable in

37.3 mV/V steps.

If the audio signal is higher than VLIM, then the gain decreases until the audio signal is just below VLIM. The

gain decrease rate (attack time) is set via the I2C interface. If the audio signal is below VLIM and the gain is

below the fixed gain, the gain will increase. The gain increase rate (release time) is set via the I2C interface. The

attack and release times are selected via I2C interface. Eight attack times are available in 350 µs / dB steps.

Sixteen release times are in 105 ms / dB steps. ATK_TIME[2:0] is Register 0x0E, Bits 0-2. REL_TIM[3:0] is

Table 3. Attack Time Selection

ATTACK TIME REGISTER

ATTACK TIME

BYTE: ATK_TIME[2:0]

( µS / STEP)

000

001

370

010

720

011

1070

100

1420

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