TLE 4261-2

Semiconductor Group

2

1998-11-01

Application Description

The IC regulates an input voltage

V

reset signal is generated for an output voltage

V

set with an external capacitor. A connected microprocessor is monitored by the

integrated watchdog circuit; if pulses are missing, the reset output is set low. The pulse

repetition rate can be set within wide limits with the capacitor for reset delay. If this input

is connected to a voltage of > 6 V, the watchdog function is deactivated. The device also

features an inhibit input, which is activated by a voltage of > 6 V and then works on this

input through internal hysteresis up to approx. 3 V. A voltage of < 2 V on the inhibit input

turns off the regulator, current drain then dropping to max. 50

Design Notes for External Components

The input capacitor

C

input voltage. The IC is protected against rise times up to 100 V/

the tuned circuit consisting of supply inductance and input capacitance with a resistor of

approx. 1

The output capacitor maintains the stability of the regulating loop. Stability is guaranteed

with a rating of 22

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 controls

the base of the series PNP 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

drops below 95.5% of its typical value for more than 2

pin 3 and an external capacitor discharged on pin 5. The reset signal is not cancelled

until the voltage on the capacitor has exceeded the upper switching threshold

V

positive-edge-triggered watchdog circuit monitors the connected microprocessor and

will likewise trigger a reset if pulses are missing. The IC can be disabled by a low level

on the inhibit input and the current consumption drops to

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

• Overload

• Overvoltage

• Overtemperature

• Reverse polarity