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TDA3608THQ

Multiple voltage regulators with switch

Philips Electronics 

Philips Semiconductors

Multiple voltage regulators with switch

Product specification

TDA3608Q; TDA3608TH

FUNCTIONAL DESCRIPTION

The TDA3608 is a multiple output voltage regulator with a

power switch, intended for use in car radios with or without

a microcontroller. Because of low-voltage operation of the

car radio, low-voltage drop regulators are used in the

TDA3608.

Backup supply

The charge of the backup capacitor connected to pin BU

can be used to supply regulator 2 for a short period when

the supply voltage VP drops to 0 V (the time depends on

the value of the capacitor).

Regulator 1

When the output voltage of regulator 2 and the supply

voltage (VP > 4.5 V) are both available, regulator 1 can be

operated by means of enable pin EN1 (see Fig.4).

Regulator 2

Regulator 2 switches on (see Fig.5) when the backup

voltage exceeds 6.5 V for the first time and switches off

when the output voltage of regulator 2 drops below 1.9 V

(this is far below an engine start).

Regulator 3

When the output voltage of regulator 2 and the supply

voltage (VP > 4.5 V) are both available, regulator 3 can be

operated by means of enable pin EN3 (see Fig.4).

Reset

When regulator 2 is switched on and the output voltage of

this regulator is within its voltage range, the reset output

(see Fig.5) will be enabled (pin RES goes HIGH through

an external pull-up resistor) to generate a reset to the

microcontroller.

The reset cycles can be extended by means of an external

capacitor connected to pin CRES. This start-up feature is

included to secure a smooth start-up of the microcontroller

at first connection, without uncontrolled switching of

regulator 2 during the start-up sequence.

Hold

Regulator 1 has an open-collector hold output (see Fig.4)

indicating that the output voltage is settled at 8.5 V.

Pin HOLD is held HIGH by an external pull-up resistor.

When the supply voltage VP drops or during high load, the

output voltage drops out-of-regulation and pin HOLD goes

LOW.

The hold output is only activated when VREG3 > 1.3 V.

When pin HOLD is connected via a pull-up resistor to the

output of regulator 3 spikes will be minimized to 1.3 V

(maximum value) because the hold output is only disabled

when VREG3 < 1.3 V.

Pin HOLD will be forced LOW when the load dump

protection is activated and also in the standby mode.

Power switch

The power switch can be controlled by means of enable

pin ENSW (see Fig.6).

Protections

All output pins are fully protected.

The regulators are protected against load dump

(regulator 1 and regulator 3 switch off at VP > 18 V) and

short-circuit (foldback current protection).

The power switch contains a foldback current protection,

but this protection is delayed at a short-circuit condition by

the reset delay capacitor. During this time the output

current is limited to at least 2 A (peak value) and

1.8 A (continuous value) at VP ≤ 18 V. During the foldback

mode the current is limited to 0.5 A (typical value).

The timing diagram is shown in Fig.7.

The foldback protection is activated when VSW < 4 V.

When regulator 2 is out-of-regulation and generates a

reset, the power switch is in the foldback mode

immediately when VSW < 4 V.

In the standby mode the voltage on the reset delay

capacitor is about 4 V and the voltage on the power switch

output is VP − 0.45 V (typical value) at ISW = 1 A. During

an overload condition or short-circuit the reset delay

capacitor will be charged to a higher voltage. The power

switch is in the high current mode while the capacitor is

charged, after this the switch is in the foldback mode

(VSW < 4 V). While the reset delay capacitor is charged the

power switch output can reach its correct output voltage.

Now the voltage on the reset delay capacitor is decreased

rapidly to 4 V. The reset output voltage is not influenced by

this change of voltages. The time of the high current mode

depends on the value of the reset delay capacitor.

At VP > 18 V the power switch is clamped at maximum

17.2 V (to avoid that external connected circuitry is being

damaged by an overvoltage) and the power switch will

switch off at load dump.

2003 Nov 28

6

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