TDA7808 datasheet(25/39 Pages) STMICROELECTRONICS

25 / 39 page

DS12230 Rev 4

25/39

TDA7808

Functional description

8.1

Voltage regulators timing

Pins D3V3 and A3V3 are respectively the digital and analog internal regulators. The D3V3

rises right after the STBY pin is at the logical value "1" and its rising time depends on the

filter capacitor; the value suggested for this filter is of min 4.7 μF.

The A3V3 rises after any command that moves the amplifier from low quiescent current

mode; the rising time depends on the combined effect of the external capacitor on the pin

and of an internal 2 ms ramp: if the capacitor value is 22 μF or lower, the internal ramp effect

is dominant and the rising time will be about 2 ms. On the other hand, when the capacitor

has a higher value, the rise time will be higher as well. The suggested value for this

capacitor is 22 μF (47 μF) at least.

8.2

SB-I Improved high efficiency principle

The TDA7808 embeds an improved high efficiency feature that minimizes the power

dissipated through the heat sink basing on the musical signal characteristic. All bridges are

connected to a common bar by means of four power switches. When an input signal goes

under a threshold that depends on the Vs level, the switch will short the corresponding

output to the common bar in such a way that it can exchange current with the other channel.

The dissipation reduction can be up to 50% compared to standard AB class.

The TDA7808 sets the high efficiency mode by default, but it can be changed through the

bits IB0 D3, D2, D1 and D0.

8.3

Input offset detector

Input offset detector aim is to avoid any possible offset that could come from the audio

signal source through I2S/TDM input stream.

For this purpose the TDA7808 input offset detector performs an evaluation of the input

signal and calculates if an offset with values higher than -19.5 dBFs is present.

Moreover, if high pass filter function is selected by means of IB3-d2, the TDA7808 will

eliminate the input offset giving a complete robustness to any disturbance or malfunction

coming from the previous audio chain blocks.

The input offset detector and high-pass filtering can be used during PLAY mode.

TDA7808 Datasheet(PDF) 25 Page - STMicroelectronics