MIPSZ2012D3R3 datasheet(31/48 Pages) STMICROELECTRONICS

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TS4621B

Application information

Doc ID 022194 Rev 2

31/48

4.3

Overview of the class-G, 2-level headphone amplifier

The TS4621B uses what is referred to as class-G operating mode. This mode is a

combination of the class-AB biasing technique and an adaptive power supply. For this

device, the power supply uses two levels: ±1.2 V and ±1.9 V.

To create the ±1.2 V and ±1.9 V levels, the device uses an internal high-efficiency step-

down converter linked with a fully capacitive inverter from AVdd. Thanks to these internally-

generated symmetrical power supply voltages, the output of the amplifier can be biased at

0 V, thus eliminating the classical bulky DC blocking output capacitors (typically more than

100

μF).

Figure 75.

TS4621B architecture

When an audio signal is playing with the TS4621B, the class-G feature adjusts in real time

the internal power supply voltage in order to achieve the best efficiency possible. In addition,

thanks to the fast transient response of the internal DC/DC converters, the switching

between ±1.2 V and ±1.9 V can be achieved without audio clipping. Moreover, the out-of-

audio band DC/DC switching frequency keeps the audio quality at a high level (distortion,

noise, etc…).

C12

2.2 uF

Css

2.2 uF

10 uF

3.3 uH

Vbat

Full capacitive

inverter

Vout

In+

In-

1.2 V to 1.9 V

-1.2 V to -1.9 V

0 V

+Vout

-Vout

Level

detector

DC/DC

control

HPVdd

PVss

AM06150

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