TDF8553J datasheet(14/47 Pages) NXP

14 / 47 page

TDF8553J_1

Objective data sheet

Rev. 01 — 3 December 2008

14 of 47

NXP Semiconductors

TDF8553J

× 50 Watt power ampliﬁer and multiple voltage regulator

8.6.5 External DC-to-DC converter

The VDCDC supply pin can be connected to an external DC-to-DC down converter

(VO ≥ 5 V) to reduce the dissipation in regulator 3. If no external DC-to-DC converter is

used, the VDCDC pin must be connected to VP.

8.6.6 Protection

All regulator and switch outputs are fully protected by foldback current limiting against load

dumps and short-circuits; see Figure 6. During a load dump all regulator outputs, except

the output of regulators 2 and 6, will go low.

The power switches can withstand ‘loss-of-ground’. This means that if pin GND becomes

disconnected, the switch is protected by automatically connecting its outputs to ground.

8.6.7 Temperature protection

If the junction temperature of a regulator becomes too high, the ampliﬁer(s) are switched

off to prevent unwanted noise signals being audible. A regulator junction temperature that

is too high is indicated by pin DIAG going LOW and is also indicated by setting bit D6 in

data byte DB2.

If the junction temperature of the regulator continues to rise and reaches the maximum

temperature protection level, all regulators and switches will be disabled except

regulators 2 and 6.

8.7 I2C-bus speciﬁcation

Fig 6.

Foldback current protection

VREGn

IOS

IOlim

IREGn

001aai698

Fig 7.

Address byte

mdb516

MSB

LSB

0 = write

1 = read

R/W

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