TDF8541JSSLASHN2 datasheet(18/54 Pages) NXP

18 / 54 page

TDF8541

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Product data sheet

Rev. 3 — 13 December 2011

18 of 54

NXP Semiconductors

TDF8541

I2C-bus controlled 4

 45 W power amplifier

7.5.3 AC load detection

The AC load detection, set with IB1[D2] = 1, is used to detect if AC-coupled speakers

such as tweeters are connected correctly. The detection requires a 19 kHz sine wave to

be applied to the inputs of the amplifier. A high current AC-load detection mode can be

selected, for example during car assembly, or a low current AC-load detection mode, for

example during switch on of car radio. The output voltage over the load impedance

generates an amplifier current. If the amplifier peak current triggers 4 times a 500 mA

(peak) threshold (or 275 mA (peak) in low current mode), the AC-load detection bit is set.

The 4 ‘threshold cross’ counter is used to prevent false AC-load detection caused by

switching the input signal on or off.

An AC-coupled speaker reduces the impedance at the output of the amplifier in a certain

frequency band. The presence of an AC-coupled speaker can be determined using a high

current mode (IB4[D1] = 1, see Figure 14) or using a low current detection mode

(IB4[D1] = 0; see Figure 14.

If, for instance, a 19 kHz input signal is generated with a peak output voltage of 2 V the

I2C-bus bits are guaranteed to be set with a total AC + DC load less than 4

 and are

guaranteed not set with a load of more than 9

; see Figure 14.

The interpretation of the line driver and amplifier mode DC load bit for AC load detection is

shown in Table 6.

Fig 13. Offset detection

001aam700

reset, setting

disabled

offset

threshold

time

Vo = (OUT+ - OUT-)

offset

threshold

time

read

→

set bit

1 second:

read

→ offset,

DBx[D2] set

1 second:

read

→ no offset,

DBx[D2] reset

Vo = (OUT+ - OUT-)

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