TPA2015D1_11 Datasheet, PDF (13/28 Pages) Texas Instruments – 2 W Constant Output Power Class-D Audio Amplifier With Adaptive Boost Converter andBattery Tracking SpeakerGuard™ AGC

TPA2015D1
www.ti.com
SLOS638A – NOVEMBER 2011 – REVISED NOVEMBER 2011
Connect a resistor between the AGC pin and ground to set the inflection point, as shown in Table 1. Leave the
AGC pin floating to disable the inflection point, keeping the limiter level constant over all supply voltages.
The maximum limiter level is fixed, as is the slope of the limiter level versus supply voltage. If different values for
maximum limiter level and slope are required, contact your local Texas Instruments representative.
Function
Constant limiter level; battery track OFF
AGC battery track option 1
AGC battery track option 2
AGC battery track option 3
Table 1. AGC Function Table
Resistor on AGC pin
Floating or connected to VBAT
39 kΩ
27 kΩ
18 kΩ
Inflection Point
disabled
3.55 V
3.78 V
3.96 V
The audio signal is not affected by the SpeakerGuard™ function unless the peak audio output voltage exceeds
the limiter level. Figure 23 shows the relationship between the audio signal, the limiter level, the supply voltage,
and the supply current.
When VBAT is greater than the inflection point, the limiter level allows the output signal to slightly clip to roughly
6% THD at 2 W into 8 Ω. This is an acceptable peak distortion level for most small-sized portable speakers,
while ensuring maximum loudness from the speaker.
Battery Tracking SpeakerGuard™ Example
Phase 1
Phase 2
Phase 3
Phase 4
Phase 5
Phase 6
Battery discharging normally; supply voltage is above inflection point; audio output remains
below limiter level.
The limiter level remains constant because the supply voltage is greater than the inflection point.
Amplifier gain is constant at fixed-gain as set by the GAIN pin. The audio output remains at a
constant loudness. The boost converter allows the audio output to swing above the battery supply
voltage. Battery supply current increases as supply voltage decreases.
Battery continues to discharge normally; supply voltage decreases below inflection point;
limiter level decreases below audio output.
The limiter level decreases as the battery supply voltage continues to decrease. SpeakerGuard™
lowers amplifier gain, reducing the audio output below the new limiter level. The supply current
decreases due to reduced output power.
Battery supply voltage is constant; audio output remains below limiter level.
The audio output, limiter level, and supply current remain constant as well.
Phone plugged in and battery re-charges; supply voltage increases.
The limiter level increases as the supply voltage increases. SpeakerGuard™ increases amplifier
gain slowly, increasing audio output. Because the TPA2015D1 supply current is proportional to the
PVOUT-to-VBAT ratio, the supply current decreases as battery supply voltage increases.
Battery supply voltage is constant; audio output is below limiter level.
SpeakerGuard™ continues to increase amplifier gain to the fixed-gain as set by the GAIN pin. The
audio output signal increases (slowly due to release time) to original value.
Battery supply voltage is constant; audio output remains below limiter level.
Amplifier gain equal to fixed-gain as set by the GAIN pin. Audio output signal does not change.
Supply current remains constant.
Copyright © 2011, Texas Instruments Incorporated
Product Folder Link(s): TPA2015D1
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