TDF8555J NXP Semiconductors, TDF8555J Datasheet - Page 9

• Manufacturer Part Number: TDF8555J
• Description: The TDF8555J is one of a new generation of complementary quad Bridge-Tied Load(BTL) audio power amplifiers with full I²C-bus controlled diagnostics, multiple voltageregulator and two power switches intended for automotive applications
• Manufacturer: NXP Semiconductors

NXP Semiconductors
7. Functional description amplifier section
TDF8555J
Product data sheet
7.1 Start-up and shut-down timing
The TDF8555J is a complementary quad Bridge-Tied Load (BTL) audio power amplifier
made using SOI-based BCDMOS technology. It contains four independent amplifiers in a
BTL configuration. 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 TDF8555J is protected against overvoltage, short-circuit, overtemperature, open
ground and open V
The diagnostics for temperature and clip levels are programmable via the I
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 diagnostic can be used to detect shorted
load, open load, short to ground or short to V
The input stage is biased at (0.23  battery voltage + 1.4 V) and can handle an input
voltage of 8 V peak. The DC input bias voltage can be measured on pin SVR. By biasing
the voltage on 0.23  battery voltage + 1.4 V (= 4.7 V at a supply voltage 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 (audible) input signal will be
generated caused by the difference in input time-constant (different AC ground and input
capacitor). This small input signal is amplified to the output and will generate plop noise at
the output.
The BCDMOS process with an isolated substrate ensures a robust amplifier (latch-up
cannot occur) and low cross-talk between the channels (every component isolated, no
substrate currents) resulting in perfect sound quality.
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 I
charged to half the supply voltage.
To enable short start-up times, the 70 k input resistance is reduced to 3 k during
start-up until just before the start-up mute release.
During start-up, the amplifier cannot distinguish between a short to ground or a speaker
fault. If a speaker fault occurs during start-up, the amplifier enters protection mode and
switches off that channel.
If the amplifier starts, and a speaker fault occurs (double-fault condition: one side of the
speaker connected to ground and one side of the speaker connected to one output), the
amplifier only sets the speaker fault detection bits.
All information provided in this document is subject to legal disclaimers.
P
connections.
Rev. 1 — 15 September 2011
4 45 W power amplifier with multiple voltage regulator
2
C-bus mode (IB1[D0] = 1), the amplifier output voltage is
P
.
TDF8555J
© NXP B.V. 2011. All rights reserved.
2
C-bus. The
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