TLE 4270

Semiconductor Group

3

1998-11-01

Application Description

The IC regulates an input voltage in the range of 5.5 V

to 26 V it produces a regulated output current of more than 550 mA. Above 26 V the

save-operating-area protection allows operation up to 36 V with a regulated output

current of more than 300 mA. Overvoltage protection limits operation at 42 V. The

overvoltage protection hysteresis restores operation if the input voltage has dropped

below 36 V. A reset signal is generated for an output voltage of

V

power-on reset can be set externally with a capacitor.

Design Notes for External Components

An input capacitor

C

circuit consisting of lead inductance and input capacitance can be damped by a resistor

of approx. 1

the regulating circuit. Stability is guaranteed at values of

C

< 3 Ω.

Circuit Description

The control amplifier compares a reference voltage, which is kept highly accurate by

resistance adjustment, to a voltage that is proportional to the output voltage and drives

the base of a series transistor via a buffer. Saturation control as a function of the load

current prevents any over-saturation of the power element.

If the output voltage decreases below 4.5 V, an external capacitor

C

discharged by the reset generator. If the voltage on this capacitor drops below

V

reset signal is generated on pin 2 (RO), i.e. reset output is set low. If the output voltage

rises above 4.5 V,

C

the voltage on the capacitor reaches

V

value of the power-on-reset time can be set within a wide range depending of the

capacitance of

C

The IC also incorporates a number of internal circuits for protection against:

• Overload

• Overvoltage

• Overtemperature

• Reverse polarity