TDA3602 datasheet(17/26 Pages) PHILIPS

17 / 26 page

July 1994

Philips Semiconductors

Product speciﬁcation

Multiple output voltage regulator

TDA3602

Example of a modern car radio design with the

TDA3602

DESIGN CONSIDERATIONS

A modern car radio set meets the following design

considerations:

1. Semi on/off logic. The radio set has to switch on/off by

pressing the on/off key or by switching the ignition

2. Security code check

3. Low quiescent current in standby (this means that the

microprocessor is off when the set is off)

4. The set must recover the state it had before an engine

start or load dump

5. Apart from HOLD, RESET and VP only two more I/O

lines are used for full on/off logic

6. Supply by 1 or 2 supply lines

7. Radio Data System (RDS) should be implemented in

the set, but this is not a regulator problem

8. Lights must switch off during load dump

Although the TDA3602 is designed only to be supplied by

a continuous supply (battery), it is also possible to use both

a continuous and a switchable supply (ignition). The

ignition can be used to supply also the TDA3602, although

in this event additional circuitry is needed.

APPLICATION CIRCUIT WITH (SEMI-)FULL ON/OFF LOGIC

The application circuit of Fig.11 will meet all the above

mentioned design considerations. Three circuit parts can

be distinguished:

Reset circuitry

A reset is required to call-up the microprocessor when it is

switched to the sleep mode or the power-on reset (first

initialization of the microprocessor). To achieve this, three

different types of resets should be generated:

1. When the set has been disconnected from the supply,

the microprocessor must be initialized at connection to

the supply for the first time. The output ports of the

microprocessor are in a random state. To ensure

correct initialization, a reset has to be generated. This

is accomplished by the power-on state of the

TDA3602. In this state the reset output is HIGH and

Regulators 1 and 2 are disabled (despite the voltage

on the state control pin Vsc being below 1.1 V). Only

after the voltage on the state control pin has risen

above 2.2 V can Regulators 1 and 2 be switched on

again by pulling the state control pin below 1.1 V.

2. In the sleep mode the microprocessor should be called

up by pressing the on/off key (normal off condition).

Now the reset is also generated by the RESET output

of the TDA3602. This reset output will go HIGH when

Vsc decreases from the value VREG3 to below 1.9 V.

3. At fault conditions

(VP below 7.1 V, VREG1 < VREG1 nominal −0.3 V or

VP > 1 8 V), HOLD drops to logic 0 and the

microprocessor switches off the set. In accordance

with the design considerations is that the mode of

operation must switch to the state it was in before an

engine start or load dump occurred. To achieve this

the HOLD output of the TDA3602 can be used to

generate a reset pulse (only when Vsc remains below

1.1 V).

The RESET and HOLD outputs of the TDA3602 are

combined to generate the reset pulses. The pulses are

created by differentiating the outputs, using capacitors

C8 and C9. The reset pulses are added by means of the

diodes D2 and D3. The time constants are:

• tresres(rise) = 3 × R7 × C8 = 3 × 10 kΩ × 1uF = 30 ms

on/off button S1 should be pressed for at least 30ms,

before the microprocessor will see this

• treshold(rise) = 3 × R7 × C9 = 5.4 ms

• tres(dis) = 3 × R8 × C8 = 140 ms

• treshold(disl) = 3 × R9 × C9 = 25 ms

the microprocessor has to wait and check if HOLD

remains LOW for at least 25 ms before it switches off;

now it is certain that a correct reset will occur to wake up

the microprocessor again.

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