TDF8541JSSLASHN2 datasheet(21/54 Pages) NXP

21 / 54 page

TDF8541

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Product data sheet

Rev. 3 — 13 December 2011

21 of 54

NXP Semiconductors

TDF8541

I2C-bus controlled 4

 45 W power amplifier

7.7 I2C-bus, legacy mode and address select pin

Pin ADSEL can select either of two amplifier modes: legacy mode or I2C-bus mode.

7.7.1 Address select (pin ADSEL)

The following amplifier functions are selected with pin ADSEL:

• Pin ADSEL shorted: (RADSEL < 470 ) legacy mode, no I2C-bus communication is

needed.

• Resistor connected between pin ADSEL and ground: where different I2C-bus

addresses can be selected with resistors.

• One I2C-bus address can be selected by either forcing a voltage on pin ADSEL or by

connecting a high ohmic resistor between pin ADSEL and VP.

To avoid address changes during low supply voltage, the address selected by the value of

resistor connected to pin ADSEL is latched at voltages below 6 V. The consequence is,

during start-up and after every power-on reset, the supply voltage must be above 6 V

otherwise the address is invalid.

7.7.2 Legacy mode (RADSEL < 470 )

The function of pin STB changes from off/operating to off/mute/operating and the amplifier

starts immediately when pin STB is put into mute or operating mode. Mute operating is

controlled via an internal timer (15 ms) to minimise mute-on plops. When pin STB is

switched directly from operating to off, first the hard mute is activated (switching to mute

within 400

s) and then the amplifier shuts down. To have a plop-free shut-down, first pin

STB should be switched to mute for 50 ms and then switched off.

7.7.3 I2C-bus mode

If pin STB is LOW, the total quiescent current is low, and the I2C-bus lines are not loaded.

When pin STB is switched HIGH, the TDF8541 enters operating mode and performs a

POR which makes pin DIAG LOW. The TDF8541 starts when IB1[D0] = 1. Bit D0 also

resets the ‘power on reset occurred’ bit (DB2[D7]) and releases pin DIAG.

Soft mute and hard mute can be activated via the I2C-bus. Soft mute can be activated

independently for the front (channels 1 and 3) and rear (channels 2 and 4), and mutes the

audio in 15 ms. Hard mute activates the mute for all channels at the same time and mutes

the audio in 400

s. Unmuting after a hard mute will be a soft unmute of approximately

15 ms. When pin STB is switched to Off mode, and the amplifier has started, first the hard

mute is activated and then the amplifier shuts down. It is possible to fully mute the

amplifiers within 400

s by making pin STB LOW, for example during an engine start.

7.7.4 I2C-bus diagnostic bits read-out/cleared after read

The amplifier’s diagnostic information can be read via the I2C-bus. The I2C-bus bits are

set if a failure occurs and are reset by the I2C-bus read command (cleared after read).

When the failure is removed, the microcontroller knows the cause of the failure by reading

the I2C-bus. The consequence of this procedure is that old information is read during the

I2C-bus read. Most real information will be gathered within two consecutive read

commands.

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