TDF8541THSLASHN2 datasheet(20/54 Pages) NXP

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TDF8541

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Product data sheet

Rev. 3 — 13 December 2011

20 of 54

NXP Semiconductors

TDF8541

I2C-bus controlled 4

 45 W power amplifier

7.5.4 Distortion clip detection

If the amplifier output starts clipping at the supply voltage or ground, the output signal

becomes distorted. If the distortion per channel exceeds a selectable threshold (2 %, 5 %

or 10 %), either pin DIAG or pin STB is activated. To be able to detect if, for instance, the

front channels (channels 1 and 3) or rear channels (channels 2 and 4) are clipping, the

clip information per channel can be directed to either pin DIAG or pin STB.

It is possible to only have the clip information on the diagnostic pins by disabling the

temperature- and load information on pin DIAG. The temperature and load protection are

still functional but can only be read via the I2C-bus.

The clip detection level can be programmed via the I2C-bus. The clip information is

blocked below a supply voltage of 10 V to avoid false clip detection during engine start, or

can be programmed to operate at the low voltage detection level of 7.5 V or 6 V.

Since it is possible to have different amplifier gain settings between the front and rear

channels and there is only one clip reference current, the clip detect levels are only

accurate for the channels with the highest gain. In line driver mode the DC-output voltage

is 0.23VP and clip detection will still indicate a clip, but the levels will not be accurate.

7.6 Line driver mode and low gain mode

The TDF8541 can be used as a line driver or as a low gain amplifier. In both situations, the

gain needs to be set to 16 dB via the I2C-bus (IB3[D5:D6] and can be independently set

for the front (channels 1 and 3) and rear (channels 2 and 4). The main difference between

line driver mode and low gain mode is the DC output voltage.

In line driver mode the TDF8541 is used to drive a separate amplifier or booster. In this

mode the DC output voltage is set to 0.23

 battery voltage and is filtered with the

capacitor connected to pin SVR (same as VSVR). The reason not to set the DC output

voltage to half the battery voltage is to allow engine starts at a battery voltage as low as

6 V. The DC output voltage remains approximately 3 V during engine start. If the DC

output voltage is set to half the battery voltage, with an engine start the common mode

voltage will change quickly from 7 V to 3 V. This drives the input stage of the booster

below the ground level.

If the TDF8541 is used as a low gain amplifier in a booster, the DC output voltage is set to

half of the supply voltage to ensure maximum undistorted output power.

The line driver and low gain modes can be selected with I2C-bus bit IB4[D2].

[1]

X = neither mode selected.

Table 7.

DC output voltage as a function of different gain settings

Channels 1 and 3

gain setting (dB)

Channels 2 and 4

gain setting (dB)

Line driver/low gain

mode IB4[D2][1]

All channels DC

output voltage (V)

0.5VP

low gain mode

0.5VP

line driver mode

0.23VP

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