TDF8541THSLASHN2 datasheet(7/54 Pages) NXP

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TDF8541

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Product data sheet

Rev. 3 — 13 December 2011

7 of 54

NXP Semiconductors

TDF8541

I2C-bus controlled 4

 45 W power amplifier

Functional description

The TDF8541 is a complementary quad BTL audio power amplifier made with SOI-based

BCDMOS technology. It contains four independent amplifiers in a BTL configuration; see

Figure 1. The amplifier remains fully operational at a battery voltage as low as 6 V. Below

6 V, a crank detector is activated to shut down the amplifier without audible plops.

The TDF8541 is protected against overvoltage, short-circuit, overtemperature, open

ground and open VP connections.

The diagnostics for temperature and clip levels are programmable via the I2C-bus, and the

information indicated at diagnostic pins DIAG and STB is selectable. The status of each

amplifier can be read separately for output offset, load or no load, short-circuit or speaker

falsely connected.

During amplifier start-up the built-in start-up diagnostics can be used to detect shorted

load, open load, short to ground or short to VP. The TDF8541 is software and hardware

compatible with its predecessor: stand-alone amplifier TDA8594 and TDA8595.

A resistor can be connected to pin ADSEL and ground to emulate an I2C-bus address that

is determined by the resistor value. Up to four different I2C-bus addresses are possible;

see Table 8. If pin ADSEL is shorted to ground, the TDF8541 operates in legacy mode. In

this mode, the I2C-bus is not needed and the function of pin STB changes from 2-level

(Stand-by mode and On mode) to a 3-level pin (Stand-by mode, On mode and mute).

The output stage of an amplifier channel consists of two PDMOS power transistors and

two NDMOS transistors in BTL configuration and ensures a high power output signal with

perfect sound quality. The BCDMOS process is used with an isolated SOI substrate which

ensures a robust amplifier, where latch-up cannot occur, and low crosstalk between the

channels with every component isolated, without substrate currents.

The input stage is biased (at 0.23

 battery voltage + 1.4 V) and can accept an input

voltage of up to 8 V (peak). The DC input bias voltage can be measured on pin SVR. At a

bias voltage of 0.23

 battery voltage + 1.4 V (= 4.7 V at a supply of 14.4 V), the input

capacitors can remain biased even with an engine start crank as low as 6 V. If the input

capacitors are allowed to discharge quickly, a small input signal is caused by a different

input time-constant due to a different AC ground and input capacitor. This small input

signal would be amplified to the output resulting in an audible plop noise.

7.1 Start-up and shut down sequence

The capacitor on pin SVR is used for smooth start-up and shut-down which prevents the

amplifier from producing switch-on or -off plop noise. Increasing the SVR capacitor value

increases start-up and shut-down time.

If the amplifier is switched on in I2C-bus mode (IB1[D0] = 1) or in legacy mode

(VSTB > 2.5 V), the amplifier output voltage rises to 1.4 V below half the supply voltage

and the output is muted. When the output reaches 1.4 V below half the supply voltage, the

start-up mute is released if the I2C-bus was set to unmute (VSTB > 5.9 V in legacy mode),

or stays in mute if the bits are set to mute (2.5 V < VSTB < 4.5 V in legacy mode).

To enable short start-up times, the 70 k

 input resistor is reduced to 3 k during start-up

until just before the start-up mute release.

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