TPA2015D1_10 Datasheet, PDF (14/27 Pages) Texas Instruments – 2 W Constant Output Power Class-D Audio Amplifier With Adaptive Boost Converter and Battery Tracking SpeakerGuard™ AGC

TPA2015D1
SLOS638 – MAY 2010
www.ti.com
Supply Current
Limiter Level
Class-D Voltage
Supply Voltage
Audio Signal
Phase 1
Phase 2
Inflection point
Phase 3
Phase 5
Phase 4
Phase 6
Figure 23. Relationship Between Supply Voltage, Current, Limiter Level, and Output Audio Signal
SpeakerGuard with Varying Input Levels
SpeakerGuard protects speakers by decreasing gain during large output transients. Figure 24 shows the
maximum output voltage at different input voltage levels. The load is 8 Ω and the gain is 15.5 dB (6 V/V).
6.0
R_L = 8 Ω + 33 µH
R_AGC = 27 kΩ
f = 1 kHz
5.0 _{Gain = 15.5 dB}
4.0
3.0
2.0
V_IN = 0.707 V_RMS
V_IN = 0.564 V_RMS
V_IN = 0.475 V_RMS
1.0
2.3 2.6 2.9 3.2 3.5 3.8 4.1 4.4 4.7 5.0
V_BAT − Supply Voltage − V
Figure 24. MAXIMUM OUTPUT VOLTAGE vs SUPPLY VOLTAGE
A 0.707 V_RMS sine-wave input signal forces the output voltage to 4.242 V_RMS, or 6.0 V_PEAK. Above 3.9 V supply,
the boost converter voltage sags due to high output current, resulting in a peak Class-D output voltage of about
5.4 V. As the supply voltage decreases below 3.9 V, the limiter level decreases. This causes the gain to
decrease, and the peak Class-D output voltage lowers.
With a 0.564 V_RMS input signal, the peak Class-D output voltage is 4.78 V. When the supply voltage is above
3.45 V, the output voltage remains below the limiter level, and the gain stays at 15.5 dB. Once the supply drops
below 3.45 V, the limiter level decreases below 4.78 V, and SpeakerGuard decreases the gain.
The same rationale applies to the 0.475 V_RMS input signal. Although the supply voltage may be below the
inflection point, audio gain does not decrease until the Class-D output voltage is above the limiter level.
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