TDF8541JSSLASHN2 datasheet(9/54 Pages) NXP

9 / 54 page

TDF8541

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Product data sheet

Rev. 3 — 13 December 2011

9 of 54

NXP Semiconductors

TDF8541

I2C-bus controlled 4

 45 W power amplifier

7.2 Engine start and low voltage operation

The voltage on pin SVR acts as a reference voltage for the input bias (set to 0.23

 battery

voltage + 2

 diode voltage V

be) and as a reference for generating the filtered half supply

voltage at the amplifier output. The capacitor connected to pin SVR improves supply

voltage ripple rejection and channel separation between the four channels.

The DC output voltage relates to the SVR voltage to prevent common mode ripple on the

speaker lines. If the supply voltage drops during an engine start, the output follows slowly

due to the SVR capacitor. To enable sufficient headroom for the output signal below a

battery voltage of 10 V, the DC-output voltage directly follows the half supply voltage. This

ensures that at low supply voltage the undistorted output power is maximized. If the

battery voltage is above 10 V, the DC-output voltage relates to the SVR voltage and is

filtered again for supply ripple; see Figure 6.

The DC input voltage follows the supply voltage slowly, due to the SVR capacitor, to

prevent audible plops, even during engine start.

If the battery voltage drops below 6 V, the low VP mute is activated. During low VP mute,

the amplifier is fast muted (about 400

s). When mute is completed, the capacitors on pin

ACGND and pin SVR are discharged to prevent audible plops.

If the battery rises again above the low VP mute threshold (6 V), and a Power-On Reset

(POR) (DB2[D7] = 1) is not detected, the amplifier starts automatically. The amplifier

restart only occurs if the SVR capacitor has been discharged to 0.7 V to prevent a start-up

plop. If the battery voltage has dropped too much that the internal registers lose their

Fig 5.

Start-up and shut-down in legacy mode

soft

mute

fast

mute

toff

td(fast-mute)

td(mute-on)

td(mute-off)

tamp-on

td(soft-mute)

DIAG

STB

mute

standby

SVR

amplifier

output

POR

001aam686

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