A timer prevents the input signal from modulating the PVOUT voltage within the audio frequency range,

eliminating the potential for audible artifacts on the Class-D output.

Figure 9-5 shows how the adaptive boost modulates with a typical audio signal. By automatically deactivating the

boost converter and passing VBAT to PVOUT, the TPA2015D1 efficiency is improved at low output power.

t − Time − s

0.0

0.5

1.0

1.5

2.0

−6

−4

−2

0

2

4

6

8

10

12

PVOUT

Gain = 20 dB

AGC = Float

Figure 9-5. Adaptive Boost Converter With Typical Music Playback

The primary external components for the boost converter are the inductor and the boost capacitor. The inductor

stores current, and the boost capacitor stores charge. As the Class-D amplifier depletes the charge in the boost

capacitor, the boost inductor replenishes charge with its stored current. The cycle of charge and discharge

occurs frequently enough to keep PVOUT within its minimum and maximum voltage specification.

The boost converter design is optimized for driving the integrated Class-D amplifier only. It lacks protection

circuitry recommended for driving loads other than the integrated Class-D amplifier.

9.3.3.1 Boost Converter Overvoltage Protection

The TPA2015D1 internal boost converter operates in a discontinuous mode to improve the efficiency at light

loads. The boost converter has overvoltage protection that disables the boost converter if the output voltage

exceeds 5.8 V. If current is forced into the PVOUT terminal, the voltage clamp will sink up to 10 mA. If more than

10 mA is forced into PVOUT, then the PVOUT voltage will increase. Refer to the Section 9.3.6 section for details.

See Section 13.1.1.2 for a list of terms and definitions used in the boost equations.

9.3.4 Operation With DACs and CODECs

Large ripple voltages can be present at the output of ΔΣ DACs and CODECs, just above the audio frequency

modulator in the DAC.

Some Class-D amplifiers have higher output noise when used in combination with these DACs and CODECs.

This is because out-of-band noise from the CODEC/DAC mixes with the Class-D switching frequencies in the

audio amplifier input stage.

The TPA2015D1 has a built-in low-pass filter that reduces the out-of-band noise and RF noise, filtering out-of-

band frequencies that could degrade in-band noise performance. The TPA2015D1 AGC calculates gain based

on input signal amplitude only.

If driving the TPA2015D1 input with 4th-order or higher ΔΣ DACs or CODECs, add an R-C low pass filter at each

of the audio inputs (IN+ and IN-) of the TPA2015D1 to ensure best performance. The recommended resistor

value is 100 Ω and the capacitor value of 47 nF.

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TPA2015D1

SLOS638C – NOVEMBER 2011 – REVISED JUNE 2022

Copyright © 2022 Texas Instruments Incorporated

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