TDF8553J datasheet(12/47 Pages) NXP

12 / 47 page

TDF8553J_1

Objective data sheet

Rev. 01 — 3 December 2008

12 of 47

NXP Semiconductors

TDF8553J

× 50 Watt power ampliﬁer and multiple voltage regulator

8.6 Voltage regulators

The voltage regulator section contains:

• Four switchable regulators and two standby regulators

• Two power switches with loss-of-ground and surge protection

• Second supply pin to reduce dissipation by means of an external DC-to-DC converter

• Backup functionality for regulator 2

The TDF8553 uses low dropout voltage regulators for use in low voltage applications.

All of the voltage regulators except for the standby regulators can be controlled via the

I2C-bus. The voltage regulator section of this device has two power switches which are

capable of delivering unregulated continuous current, and has several fail-safe protection

modes. It conforms to peak transient tests and protects against continuous high voltage

(24 V), short-circuits and thermal stress. Standby regulators 2 and 6 will try to maintain

output for as long as possible even if a thermal shut-down or any other fault condition

occurs. During overvoltage stress conditions, all outputs except regulators 2 and 6 will

switch off and the device will be able to supply a minimum current for an indeﬁnite amount

of time sufﬁcient for powering the memory of a microcontroller and bus controller

functionality. Provision is made for an external reserve supply capacitor to be connected

to pin BUCAP which can store enough energy to allow regulator 2 to supply a

microcontroller for a period long enough for it to prepare for a loss-of-voltage.

8.6.1 Standby regulator outputs

Standby outputs (regulators 2 and 6) are used for the microcontroller and bus controller

supply. These regulators will not shut down with the switched regulators and cannot be

controlled by the I2C-bus. The standby regulators will not shut down during load dump

transients or by high temperature protection.

8.6.2 Backup capacitor

The backup capacitor (Cbackup) is used as a backup supply for the regulator 2 output when

the battery supply voltage (VP) cannot support the regulator 2 voltage.

Fig 4.

Ampliﬁer output during supply voltage drop

(V)

t (s)

SVR voltage

vehicle engine start

headroom voltage

amplifier

DC output voltage

001aai692

8.4

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