TDF8544
NXP Semiconductors
I2C-bus controlled 4 50 W power amplifier
V
P
DIAG
POR
on
STB
mute
standby
SVR
fast
mute
t
amp-on
soft
mute
t
off
amplifier
output
t
d(mute-off)
t
t
t
d(fast-mute)
d(soft-mute)
d(mute-on)
001aam686
Fig 5. Start-up and shut-down in legacy mode
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 Vbe) 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
TDF8544
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 2 — 29 August 2011
9 of 54
NXP [ NXP ]
